elp 4003 lte air interface

LTE Air InterfaceESB 4003 R2D

Student text

Disclaimer

This book is a training document and contains simplifications. Therefore, it mustnot be considered as a specification of the system.

The contents of this document are subject to revision without notice due to ongoingprogress in methodology, design and manufacturing.

ENKI Adam Girycki assumes no legal responsibility for any error or damage resultingfrom the usage of this document.

Copyright c⃝ April 28, 2014 by ENKI Adam Girycki.

This document was produced in Poland by ENKI Adam Girycki. It is used fortraining purpose only and may not be copied or reproduced in any manner withoutthe express written consent of ENKI.

This document number ESB 4003 R2D supports course number ELP 4003 R2D.

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Contents

1 OFDMA principles 51.1 Two way communication . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.1.1 FDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.1.2 TDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.2 Access network evolution overview . . . . . . . . . . . . . . . . . . . . 6

1.2.1 1G FDMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.2.2 2G TDMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1.2.3 3G WCDMA . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

1.2.4 4G OFDMA . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

1.3 Complex numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

1.3.1 Rectangular notation . . . . . . . . . . . . . . . . . . . . . . . 12

1.3.2 Polar notation . . . . . . . . . . . . . . . . . . . . . . . . . . 13

1.3.3 Relation between rectangular and polar notation . . . . . . . . 14

1.3.4 Euler’s formula . . . . . . . . . . . . . . . . . . . . . . . . . . 14

1.3.5 Exponential notation . . . . . . . . . . . . . . . . . . . . . . . 14

1.4 Fourier analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

1.4.1 Fourier Transform (FT) . . . . . . . . . . . . . . . . . . . . . 15

1.4.2 Discrete Fourier Transform (DFT) and Fast Fourier Transform(FFT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

1.5 Orthogonal Frequency Division Multiplexing (OFDM) concept . . . . . 20

1.5.1 OFDM transmitter . . . . . . . . . . . . . . . . . . . . . . . . 22

1.5.2 OFDM receiver . . . . . . . . . . . . . . . . . . . . . . . . . . 22

1.6 Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

2 EPS architecture 272.1 LTE requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

2.2 EPS architectural principles . . . . . . . . . . . . . . . . . . . . . . . 29

2.2.1 Evolved Packet Core (EPC) . . . . . . . . . . . . . . . . . . . 29

2.2.2 Evolved UTRAN (E-UTRAN) . . . . . . . . . . . . . . . . . . 30

2.3 Strata . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

2.3.1 Non-Access Stratum (NAS) . . . . . . . . . . . . . . . . . . . 31

2.3.2 Access Stratum (AS) . . . . . . . . . . . . . . . . . . . . . . 32

2.4 EPS Bearer and QoS . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

2.4.1 EPS Bearer . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

2.4.2 Quality of Service (QoS) . . . . . . . . . . . . . . . . . . . . . 34

2.5 Integration with 2G and 3G . . . . . . . . . . . . . . . . . . . . . . . 36

2.6 Interfaces overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

2.7 Evolved Packet Core (EPC) functions . . . . . . . . . . . . . . . . . . 42

2.7.1 Mobility Management Entity node . . . . . . . . . . . . . . . 42

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2.7.2 Packet Data Network Gateway (P-GW) and Serving Gateway(S-GW) nodes . . . . . . . . . . . . . . . . . . . . . . . . . . 42

2.7.3 Mobility Management Entity (MME) and S-GW pooling concept 432.8 Long Term Evolution (LTE) functions . . . . . . . . . . . . . . . . . . 45

2.8.1 LTE general principles . . . . . . . . . . . . . . . . . . . . . . 452.8.2 Evolved Node B (eNB) functionality . . . . . . . . . . . . . . 46

3 LTE signalling 493.1 User plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 493.2 Control plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 503.3 Protocols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

3.3.1 Radio Resource Control (RRC) . . . . . . . . . . . . . . . . . 503.3.2 Packet Data Convergence Protocol (PDCP) . . . . . . . . . . 523.3.3 Radio Link Control (RLC) . . . . . . . . . . . . . . . . . . . . 533.3.4 Medium Access Control (MAC) . . . . . . . . . . . . . . . . . 53

3.4 Radio interface structure . . . . . . . . . . . . . . . . . . . . . . . . . 55

4 LTE radio interface introduction 574.1 Channel structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

4.1.1 Logical channels . . . . . . . . . . . . . . . . . . . . . . . . . 574.1.2 Transport channels . . . . . . . . . . . . . . . . . . . . . . . . 584.1.3 Physical channels . . . . . . . . . . . . . . . . . . . . . . . . 59

4.2 Time domain structure . . . . . . . . . . . . . . . . . . . . . . . . . . 614.2.1 Frequency Division Duplex (FDD) . . . . . . . . . . . . . . . . 614.2.2 Time Division Duplex (TDD) . . . . . . . . . . . . . . . . . . 62

4.3 Frequency domain structure . . . . . . . . . . . . . . . . . . . . . . . 634.4 Scheduling Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 654.5 Virtual Resource Block . . . . . . . . . . . . . . . . . . . . . . . . . . 65

4.5.1 VRB of localized type . . . . . . . . . . . . . . . . . . . . . . 674.5.2 VRB of distributed type . . . . . . . . . . . . . . . . . . . . . 67

4.6 System spectral efficiency . . . . . . . . . . . . . . . . . . . . . . . . 67

5 LTE downlink physical channels 715.1 Cell search . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 715.2 P-SS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 725.3 S-SS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 735.4 RS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 755.5 PBCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

5.5.1 MIB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 785.5.2 SIB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

5.6 PCFICH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795.7 PDCCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

5.7.1 PDCCH usage . . . . . . . . . . . . . . . . . . . . . . . . . . 805.7.2 PDCCH mapping . . . . . . . . . . . . . . . . . . . . . . . . . 815.7.3 PDCCH format . . . . . . . . . . . . . . . . . . . . . . . . . . 815.7.4 PDCCH processing . . . . . . . . . . . . . . . . . . . . . . . . 815.7.5 PDCCH blind decoding . . . . . . . . . . . . . . . . . . . . . 83

5.8 PDSCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 845.8.1 CRC attachment . . . . . . . . . . . . . . . . . . . . . . . . . 885.8.2 Code block segmentation . . . . . . . . . . . . . . . . . . . . 88

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5.8.3 Channel coding . . . . . . . . . . . . . . . . . . . . . . . . . . 885.8.4 Rate matching . . . . . . . . . . . . . . . . . . . . . . . . . . 895.8.5 Code block concatenation . . . . . . . . . . . . . . . . . . . . 925.8.6 Scrambling . . . . . . . . . . . . . . . . . . . . . . . . . . . . 925.8.7 Modulation mapper . . . . . . . . . . . . . . . . . . . . . . . 925.8.8 Layer mapper . . . . . . . . . . . . . . . . . . . . . . . . . . . 925.8.9 Precoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 955.8.10 Resource element mapping . . . . . . . . . . . . . . . . . . . 98

5.9 PHICH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 995.10 PMCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 995.11 Downlink physical channels modulation summary . . . . . . . . . . . . 100

6 LTE uplink physical channels 1016.1 PUSCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1026.2 Uplink reference signals . . . . . . . . . . . . . . . . . . . . . . . . . . 104

6.2.1 RS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1046.2.2 SRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

6.3 PUCCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1056.3.1 PUCCH format 1A/1B . . . . . . . . . . . . . . . . . . . . . . 1076.3.2 PUCCH format 1 . . . . . . . . . . . . . . . . . . . . . . . . . 1086.3.3 PUCCH format 2 . . . . . . . . . . . . . . . . . . . . . . . . . 108

6.4 PRACH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

7 Physical layer procedures 1137.1 Timing advance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

7.1.1 Uplink-downlink frame timing . . . . . . . . . . . . . . . . . . 1137.1.2 Timing advance range . . . . . . . . . . . . . . . . . . . . . . 1137.1.3 Random access . . . . . . . . . . . . . . . . . . . . . . . . . . 1137.1.4 Other cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1157.1.5 Maintenance of uplink time alignment . . . . . . . . . . . . . 116

7.2 Random Access (RA) . . . . . . . . . . . . . . . . . . . . . . . . . . . 1167.3 Resource allocation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

7.3.1 Resource allocation type 0 . . . . . . . . . . . . . . . . . . . . 1197.3.2 Resource allocation type 1 . . . . . . . . . . . . . . . . . . . . 1207.3.3 Resource allocation type 2 . . . . . . . . . . . . . . . . . . . . 120

7.4 MIMO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1207.4.1 Spatial multiplexing . . . . . . . . . . . . . . . . . . . . . . . 1217.4.2 Transmit diversity . . . . . . . . . . . . . . . . . . . . . . . . 1237.4.3 Transmission modes . . . . . . . . . . . . . . . . . . . . . . . 1237.4.4 MIMO antennas . . . . . . . . . . . . . . . . . . . . . . . . . 124

7.5 UE reporting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1267.5.1 CQI definition . . . . . . . . . . . . . . . . . . . . . . . . . . 1277.5.2 Aperiodic CQI/PMI/RI reporting using PUSCH . . . . . . . . 1277.5.3 Periodic CQI/PMI/RI reporting using PUCCH . . . . . . . . . 129

7.6 Modulation order and transport block size determination . . . . . . . . 1307.6.1 Modulation determination . . . . . . . . . . . . . . . . . . . . 1317.6.2 Transport block size determination . . . . . . . . . . . . . . . 131

7.7 UL power control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1347.7.1 PUSCH power control . . . . . . . . . . . . . . . . . . . . . . 1347.7.2 PUSCH power control example . . . . . . . . . . . . . . . . . 137

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8 LTE mobility 1418.1 Idle mode mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

8.1.1 PLMN selection . . . . . . . . . . . . . . . . . . . . . . . . . 1428.1.2 Cell selection . . . . . . . . . . . . . . . . . . . . . . . . . . . 1448.1.3 Cell reselection . . . . . . . . . . . . . . . . . . . . . . . . . . 146

8.2 Connected mode mobility . . . . . . . . . . . . . . . . . . . . . . . . . 1488.2.1 X2 handover . . . . . . . . . . . . . . . . . . . . . . . . . . . 1498.2.2 Event triggered reporting . . . . . . . . . . . . . . . . . . . . 1518.2.3 A3 event . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

A System information 157

List of Figures 165

List of Tables 167

Acronyms 175

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1 OFDMA principles

1.1 Two way communication

In order to provide two way communication, so called duplex, two directions oftransmission must exist and they must be separated from each other to avoid col-lisions. Transmission from the User Equipment (UE) to the Base Station (BS) isreferred to as Uplink (UL), while the transmission from the BS to the UE is referredto as Downlink (DL), see Figure 1.1.

Figure 1.1: Two way communication.

The UL and DL transmissions can be separated in frequency or time domain, aspresented in Figure 1.2.

Figure 1.2: Frequency Division Duplex (FDD) and Time Division Duplex (TDD).

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1 OFDMA principles

1.1.1 FDD

The FDD system uses different frequency bands for UL and DL, separated by theduplex distance, see Figure 1.2. In case of FDD, the UL is usually placed on thelower frequency band because the transmission of lower frequency radio wave re-quires less energy comparing to the higher frequency band, on which the DL isplaced. In FDD solution the transmission and reception may take place contin-uously or discontinuously. An example of the FDD system is Global System forMobile communication (GSM).

1.1.2 TDD

The TDD system uses the same frequency band for both UL and DL, which istime shared as presented in Figure 1.2. TDD requires only one frequency to realisetwo way communications, which may be an advantage when the availability of radioresources is a limiting factor. On the other hand, to avoid any collisions, TDD systemrequires a time structure (synchronisation) to separate the UL and DL transmission,which is always discontinuous. An examples of the TDD system is cordless telephonysystem.

1.2 Access network evolution overview

Apart from duplex transmission separation, a harmonised access of multiple UEs tothe shared radio resources must exist, see Figure 1.3. In uplink direction a numberUEs transmit to the base station. Thus the multiple access technology is required,which allows the base station to separate transmissions from different UEs. Indownlink direction a single base station has to keep a connection with multiple users.For that reason a multiple access method is applied, which allows multiplexing ofsignals at the base station and demultiplexing the signal at the receiving side.

Figure 1.3: Multiple access.

Each generation of cellular telecommunications system provided different, more ef-fective, radio access technology, which are discuss in the next sections. The brieflysummary of cellular technologies evolution is presented in Figure 1.4.

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Figure 1.4: Cellular technologies evolution.

1.2.1 1G FDMA

1st Generation (1G), the first generation of wireless telecommunications technology,was introduced in the 1980s and it was an analogue system. The offered service wasthe voice.

Examples of 1G system:

• Nordic Mobile Telephony (NMT) introduced in 1981 and developed in Nordiccountries, Switzerland, Netherlands, Eastern Europe and Russia

• Advanced Mobile Phone Systems (AMPS) introduced in 1983 and developedin North America and Australia

In 1G system, Frequency Division Multiple Access (FDMA) method of radio re-sources usage was applied. The available radio resources were divided in frequencydomain. For each connection a separate bandwidth was allocated and the user trans-mission on the allocated channel was continuous, which is illustrated in Figure 1.5.The allocated one way channel had bandwidth of 25 kHz in NMT and 30 kHz incase AMPS, resulting in a total of 50 kHz in NMT and 60 kHz in AMPS for eachduplex channel.

1.2.2 2G TDMA

2G, the second generation of wireless telecommunications technology, was introducedin 1990s. It was a digital system. The offered services were voice, Short MessageService (SMS), Circuit Switched (CS) data transfer with the rate of 9.6 kbit/s.

Examples of 2G systems:

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1 OFDMA principles

Figure 1.5: Frequency Division Multiple Access (FDMA).

• GSM introduced in 1991 and used across more than 212 countries and territo-ries.

• Digital Advanced Mobile Phone Systems (D-AMPS) introduced 1991 and usedin North America.

• CDMAOne introduced in 1995 and used in the Americas and parts of Asia.

GSM, which is the dominant 2G system, employs the Time Division Multiple Access(TDMA) method of radio resources usage combined with FDMA. Available radioresources are first divided into Radio Frequency (RF) channels of 200 kHz bandwidth(FDMA concept) and next each RF channel is divided in time domain into timeslots(TDMA concept). A certain number of timeslots create so called TDMA frame. Thenumber of timeslots in the TDMA frame is system specific. In GSM system eighttimeslots make up the TDMA frame. A user has a cyclic access to the common radioresources during the allocated timeslot. Thus the transmission is discontinuous. TheFigure 1.6 presents the TDMA system with 4 timeslots in the TDMA frame.

Figure 1.6: Time Division Multiple Access (TDMA).

General Packet Radio Service (GPRS), which is an add-on to the CS GSM also called2.5G, offers Packet Switched (PS) data transfer with the rate of approximately 50kbps.

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Enhanced GPRS (EGPRS), also called 2.75G, offers higher date rate of PS datatransfer with the maximum rate of approximately 500 kbps, thanks to higher ordermodulation.

1.2.3 3G WCDMA

3G, the third generation of wireless telecommunication technology, was introducedin 2000s.

Examples of 3G system:

• CDMA2000 introduced in 2000 in South Korea and used in Asia, America andAfrica.

• Universal Mobile Telecommunications System (UMTS) introduced in 2001 inJapan and used in Europe, Asia and Africa.

3G systems employ Code Division Multiple Access (CDMA) method of radio re-sources usage. CDMA allows for simultaneous transmission of multiple users inthe same frequency band, which is presented in Figure 1.7. Separation of differentconnections is achieved by means of different codes. The codes must be orthogonal(independent of each other).

Figure 1.7: Code Division Multiple Access (CDMA).

In CDMA2000 the initial frequency band width was 1.25 MHz, which was nexttripled to 3x1.25 MHz.

In UMTS, the Wideband Code Division Multiple Access (WCDMA) method is ap-plied, which utilizes wide frequency band of 5 MHz. Wide frequency channel allowsfor lowering the power density, thus signal may be even weaker than thermal noiselevel.

High Speed Packet Access (HSPA) provides downlink throughput of approximately14 Mbps, while Evolved HSPA (also called HSPA+) provides throughput of 84Mbps.

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1 OFDMA principles

1.2.4 4G OFDMA

4G, the fourth generation of mobile telecommunications technology, must support 1Gbit/s downlink bit rate. Currently there is no system, that is able to support mobilecommunications with the required bit rate. However there are two technologies,which are on a way to achieve this goal in the nearest future:

• LTE offers approximately 100 Mbit/s bit rate. The world’s first publicly avail-able LTE-service was opened in the two Scandinavian capitals Stockholm andOslo on the 14 December 2009.

• Worldwide Interoperability for Microwave Access (WiMAX) offers approxi-mately 40 Mbit/s bit rate. WiMAX access was used to assist with communi-cations in Aceh, Indonesia, after the tsunami in December 2004.

Both LTE and WiMAX employ Orthogonal Frequency Division Multiple Access(OFDMA) method of radio resources usage. Theoretical foundation of OFDMAhad been already laid in 1960’, but due to high costs and lack of appropriate tech-nologies for a long time it remained purely theoretical. This situation has changedwith advent of cheap, small and fast microchips capable of processing the FFT andInverse Fast Fourier Transform (IFFT) algorithms. Nowadays, OFDM is widelyused in wireless networking (Wireless Local Area Network (WLAN)), digital televi-sion (Digital Video Broadcasting – Terrestrial (DVB-T)), audio broadcasting (Digi-tal Audio Broadcasting (DAB)) and broadband wireless communications (WiMAX,LTE).

OFDMA is a special type of the FDMA. OFDMA allows for transfer messagessimultaneously, using multiple narrow ranges of frequencies, called subcarriers, seeFigure 1.8.

Figure 1.8: Orthogonal Frequency Division Multiple Access (OFDMA).

To avoid Inter Carrier Interference (ICI), in ordinary FDMA system, all such subcar-riers are separated in frequency domain with guard bands, therefore some spectrumis wasted. OFDM provides much better spectrum efficiency, as it does not need gapsbetween subcarrier bands. Moreover, the subcarrier bands are overlapping, whichallows to additionally save some spectrum. ICI is mitigated here by taking advan-tage of the fact that under the following conditions the subcarriers are orthogonalwith one another:

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• The careful choice of subcarrier spacing. The subcarrier spacing ∆f should beexactly equal to the reciprocity of the OFDMA symbol duration Tsymbol, seeFigure 1.9, which provides that the subcarriers are mathematically orthogonaland thus independent.

• Keeping the synchronisation in the frequency domain, providing there are nofrequency shifts, e.g. due to Doppler effects.

Figure 1.9: OFDM subcarriers.

Multiplexing and demultiplexing of OFDMA symbols into subcarriers can be per-formed using Inverse Inverse Discrete Fourier Transform (IDFT) and DFT. Thesemathematical procedures, that transform signal from frequency to time domain andopposite, can be implemented with IFFT and FFT algorithms.

The presented above FDMA, TDMA and CDMA multiple access methods are singlecarrier modulation. OFDMA is a multi carrier modulation. In other words, itmeans that a large number of closely spaced orthogonal subcarriers are used tocarry data. Each subcarrier is modulated with a conventional modulation scheme(such as quadrature amplitude modulation or phase shift keying) at a low symbolrate, maintaining total data rates similar to conventional single carrier modulationschemes in the same bandwidth.

Advantages of OFDMA:

• OFDMA effectively diminishes also the problem of multipath selective fad-ing. Due to multipath radio waves propagation in typical urban environment,signal at the receiver can be constructively or destructively interfered by thesame signal delayed over different path. This effect can dramatically changedepending on frequency used as a signal carrier – some of the frequencies willsuffer from deep fading, while neighbouring ones may not be affected at all. As

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1 OFDMA principles

OFDMA uses very small subcarrier widths, the fading within every subcarriercan be considered as relatively flat.

• Another problem mitigated by OFDMA is Inter Symbol Interference (ISI).One of the causes of this effect is signal reflection from distant object (typi-cally mountain). The delayed signal, which propagates over much longer path,interferes with the direct signal because it carries another (older) symbol thanthe direct signal and therefore the receiver is unable to detect the correct sym-bol. The ISI effect is diminished when the symbol duration is longer, thus onlyvery far objects will lead to ISI. But the signal reflected from very far objectis usually week enough and does not lead to interference. In OFDMA, thesymbol duration can be lengthened, because a few symbols can be transmittedsimultaneously on different subcarriers. As already mentioned, longer symbolmakes the radio path less vulnerable to ISI. Additionally, to avoid overlapping,the adjacent symbols are always separated in time by short guard period. Inthe guard period, from technical reasons, it is not effective to stop transmissionat all, thus, so called, cyclic prefix is inserted here, which is simply a copy ofthe signal tail end.

• OFDMA can achieve a higher Multiple Input Multiple Output (MIMO) spec-tral efficiency due to providing flatter frequency channels than a CDMA rakereceiver can.

• No cell size breathing as more users connect.

Recognised disadvantages of OFDMA:

• Higher sensitivity to frequency offsets and phase noise.

• Asynchronous data communication services such as web access are charac-terised by short communication bursts at high data rate. Few users in a basestation cell are transferring data simultaneously at low constant data rate.

• The complex OFDMA electronics, including the FFT algorithm and forwarderror correction, is constantly active independent of the data rate, which isinefficient from power consumption point of view, while OFDMA combinedwith data packet scheduling may allow that the FFT algorithm hibernatesduring certain time intervals.

• The OFDMA diversity gain, and resistance to frequency-selective fading, maypartly be lost if very few sub-carriers are assigned to each user, and if the samecarrier is used in every OFDMA symbol. Adaptive sub-carrier assignmentbased on fast feedback information about the channel, or sub-carrier frequencyhopping, is therefore desirable.

• Dealing with co-channel interference from nearby cells is more complex inOFDMA than in CDMA. It would require dynamic channel allocation withadvanced coordination among adjacent base stations.

• The fast channel feedback information and adaptive sub-carrier assignment ismore complex than CDMA fast power control.

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1.3 Complex numbers

1.3 Complex numbers

Complex numbers are used in OFDMA signal processing. A complex number is anumber comprising a real (Re) and imaginary (Im) part.

1.3.1 Rectangular notation

The complex number can be written in the form of rectangular notation (also calledCartesian notation) a + ib, where a and b are real numbers, and i is the standardimaginary unit with the property i2 = −1. Figure 1.10 shows geometric representa-tion of a complex number z = a+ib in the complex plane. The complex plane can bethought of as a Cartesian plane, with the real part of a complex number representedby a displacement along the x-axis, and the imaginary part by a displacement alongthe y-axis.

Figure 1.10: Geometric representation of a complex number in the rectangularnotation in a complex Cartesian plane.

Each complex number z has a conjugate z∗, which has the same real part butopposite imaginary part, see 1.11:

z = a+ ib (1.1)

z∗ = a− ib (1.2)

1.3.2 Polar notation

Figure 1.12 presents another notation, so called polar notation, of a complex number.In the polar plane the complex number is represented by its modulus (absolute value)r and argument (angle) φ.

1.3.3 Relation between rectangular and polar notation

Relation between rectangular and polar notation of a complex number is the follow-ing:

a = r cosφ (1.3)

b = r sinφ (1.4)

15

1 OFDMA principles

Figure 1.11: Conjugate z∗ of a complex number z.

Figure 1.12: Geometric representation of a complex number in the polar notation.

Thus, the complex number z = a+ ib may be expressed as follows:

z = a+ ib = r cosφ+ ir sinφ = r(cosφ+ i sinφ) (1.5)

1.3.4 Euler’s formula

Leonhard Euler, Swiss mathematician and physicist, discovered a mathematical re-lationship between the trigonometric functions (sin and cos) and the complex expo-nential function (see also Figure 1.13):

cosφ+ i sinφ = eiφ (1.6)

Euler’s formula was called by Richard Feynman ”one of the most remarkable, almostastounding, formulas in all of mathematics”.

1.3.5 Exponential notation

Using the Euler’s formula the complex number z may be written as follows, whichis called the exponential notation of a complex number:

z = r(cosφ+ i sinφ) = reiφ (1.7)

16

1.4 Fourier analysis

Figure 1.13: Euler’s formula.

In the exponential notation certain calculations, particularly multiplication and di-vision of complex numbers, are easier than in rectangular notation. On the otherhand, addition and subtraction are easier with the use of rectangular notation. Theexponential notation of a complex number is in widespread use in engineering andscience.

Using the Euler’s formula the conjugate z∗ may be written as:

z∗ = e−iφ (1.8)


1.4.1 Fourier Transform (FT)

Fourier Transform (FT) is an operation that transforms time domain function intofrequency domain function. Therefore FT is often called the frequency domainrepresentation of the original time domain function, see Figure 1.14.

1.4.2 Discrete Fourier Transform (DFT) and Fast FourierTransform (FFT)

Discrete Fourier Transform (DFT) is a specific kind of FT. The input to the DFTis a finite sequence of real or complex numbers making the DFT ideal for processinginformation stored in computers. In particular, the DFT is widely employed insignal processing and related fields to analyse the frequencies contained in a sampledsignal, to solve partial differential equations, and to perform other operations suchas convolutions or multiplying large integers.

DFT transforms the sequence of N complex numbers a0, a1, ..., aN−1 (usually in timedomain) into a sequence of A0, A1, ..., AN−1 complex numbers (usually in frequency

17

1 OFDMA principles

Figure 1.14: Fourier Transform (FT) principles.

18


domain) according to the following formula:

Ak =

N−1∑n=0

anwkn k = 0, ..., N − 1 (1.9)

w = e−2πN

i (1.10)

The inverse transform to the DFT, which transforms the sequence of complex num-bers Ak back to the sequence of complex values an, is called Inverse Discrete FourierTransform (IDFT) and is given by the following formula:

an =1

N

N−1∑k=0

Akw−kn n = 0, ..., N − 1 (1.11)

In practice, the DFT can be computed efficiently using a Fast Fourier Transform(FFT) algorithm and IDFT using Inverse Fast Fourier Transform (IFFT) algo-rithm.

DFT example

We are going to apply the DFT to the following sequence of N = 8 numbers in thetime domain:

a = [2, 1, 0, 1, 2, 1, 0, 1] (1.12)

We will show that the DFT of the above sequence is the following sequence ofnumbers in the frequency domain:

A = [8, 0, 4, 0, 0, 0, 4, 0] (1.13)

Figure 1.15 shows the graphical presentation of the example, where the sequenceof real numbers an is transformed into the sequence of complex numbers Ak. Thecomplex numbers Ak are expressed by their modulus r and argument φ (see section1.3). The modulus r represents the amplitude of the cosinusoidal signal of a givenfrequency f and the argument φ corresponds to the phase shift of the cosinusoidalsignal. Because, in this example, the phase shift of the cosinusoidal signals is zero(which means that the imaginary parts of complex numbers Ak are equal zero)therefore Ak are actually real numbers. For the sequence of 8 numbers, the DFTformula may be expressed by the following matrix form:

A0

A1

A2

A3

A4

A5

A6

A7

=

1 1 1 1 1 1 1 1

1 w w2 w3 w4 w5 w6 w7

1 w2 w4 w6 w8 w10 w12 w14

1 w3 w6 w9 w12 w15 w18 w21

1 w4 w8 w12 w16 w20 w24 w28

1 w5 w10 w15 w20 w25 w30 w35

1 w6 w12 w18 w24 w30 w36 w42

1 w7 w14 w21 w28 w35 w42 w49

·

a0a1a2a3a4a5a6a7

(1.14)

19

1 OFDMA principles

Figure 1.15: Example of the Discrete Fourier Transform (DFT).

w = e−2π8i = e−

π4i = cos

(π4

)− i sin

(π4

)=

1√2− i√

2(1.15)

When raising the coefficient w to any integral power, one of eight values is obtained,which are illustrated in Figure 1.16. Let us denote these eight complex values byarrows according to Figure 1.16. Now, the matrix form of DFT can be noted in thefollowing way:

A0

A1

A2

A3

A4

A5

A6

A7

=

→ → → → → → → →→ ↘ ↓ ↙ ← ↖ ↑ ↗→ ↓ ← ↑ → ↓ ← ↑→ ↙ ↑ ↘ ← ↗ ↓ ↖→ ← → ← → ← → ←→ ↖ ↓ ↗ ← ↘ ↑ ↙→ ↑ ← ↓ → ↑ ← ↓→ ↗ ↑ ↖ ← ↙ ↓ ↘

·

2

1

0

1

2

1

0

1

(1.16)

We may calculate Ak numbers from the above matrix notation. As an exampleA0, A1 and A2 are calculated below:

A0 = 1 · 2 + 1 · 1 + 1 · 0 + 1 · 1 + 1 · 2 + 1 · 1 + 1 · 0 + 1 · 1 = 8 (1.17)

20


Re

Im

Figure 1.16: The coefficient wn in the DFT for N = 8.

A1 = 1 · 2 +(

1√2− i√

2

)· 1(−i) · 0 +

(− 1√

2− i√

2

)· 1+

+ (−1) · 2 +(− 1√

2+

i√2

)· 1 + i · 0 +

(1√2+

i√2

)· 1 = 0

(1.18)

A2 = 1 · 2− i · 1− 1 · 0 + i · 1 + 1 · 2− i · 1− 1 · 0 + i · 1 = 4 (1.19)

You may calculate the remaining Ak values to confirm that the DFT transformsthe sequence a = [2, 1, 0, 1, 2, 1, 0, 1] into the sequence A = [8, 0, 4, 0, 0, 0, 4, 0]. Itis important to observe that the duration of our signal sample in the time domainwas 8 s, while the shift between transformed signals in frequency domain is equal18 s =

18Hz.

Inverse Discrete Fourier Transform (IDFT) example

We are going show that the IDFT transforms the sequence of N = 8 numbers in thefrequency domain:

A = [8, 0, 4, 0, 0, 0, 4, 0] (1.20)

back into the following sequence of numbers in the time domain:

a = [2, 1, 0, 1, 2, 1, 0, 1] (1.21)

Values an may be calculated from formula 1.11, as presented below, and values w−n

are shown in Figure 1.17:

a0 =1

N

N−1∑k=0

Ak =1

8(8 + 0 + 4 + 0 + 0 + 0 + 4 + 0) = 2 (1.22)

21

1 OFDMA principles

a1 =1

N

N−1∑k=0

Akw−k =

1

8

(8w−0·1 + 4w−2·1 + 4w−6·1) =

=1

8(8 + 4i− 4i) = 1

(1.23)

a2 =1

N

N−1∑k=0

Akw−2k =

1

8

(8w−0·2 + 4w−2·2 + 4w−6·2) =

=1

8(8− 4− 4) = 0

(1.24)

Figure 1.17: The coefficient w−n in the IDFT for N = 8. When comparing withFigure 1.16 notice that w−n is a conjugate of wn.

Figure 1.18 shows the graphical presentation of the IDFT example.

1.5 OFDM concept

The OFDM concept, which uses DFT, is shown in Figure 1.19. In the picture, theinformation to be transmitted is represented by different Ak values. The process ofconverting bits into Ak values is called modulation. Each of the Ak values is senton another subcarrier. In the picture there are N = 10 subcarriers. Ak values,which are sent on different subcarriers, are represented by different heights of thebars. With the use of IDFT the Ak values are transformed to signal in time domain,which is physically transmitted during symbol time Tsymbol. The time domain signalis denoted by an values and represented by circles. Because there are 10 bars inthe frequency domain before DFT, therefore there are also 10 circles of the timedomain signal after IDFT. As already mentioned, the 10 time domain samplesare to be transmitted during Tsymbol, therefore the time between samples is equal

Ts =Tsymbol

10 .

22

1.5 OFDM concept

Figure 1.18: Graphical presentation of the IDFT example.

23

1 OFDMA principles

So far we had to do with digital operations (modulation and IDFT are digital opera-tions). Next, the 10 time domain circles an are used to generate an analogue signal,which is physically transmitted from an antenna.

Figure 1.19: OFDM concept.

The receiver performs an opposite operation. It samples the time domain signalevery Ts and collects 10 time domain samples an, which are next transformed, withuse of the DFT, to frequency domain values Ak. The frequency domain values Ak

carry information about bits which were transmitted. The bits are retrieved bydemodulation of values Ak.

After time Tsymbol the next symbol may be transmitted. Figure 1.19 illustratestransmission of 3 symbols. Please observe that there could be a break betweenconsecutive symbols transmission. This break is used to transmit cyclic prefix.

1.5.1 OFDM transmitter

In OFDM the carrier signal is a sum of orthogonal subcarriers. In each subcarrierprocessing Quadrature Amplitude Modulation (QAM) or Phase Shift Keying (PSK)can be used. A simplified scheme of an OFDM transmitter has been shown in Figure1.20.

s[i] is input bit stream. First, bits are separated into N parallel streams. Streamsare assigned for Quadrature Amplitude Modulation (QAM) or Phase Shift Keying(PSK) modulation. Depending on the modulation, subcarriers may have differenttransmission bit rate.

Next, IFFT is computed for the sequence of complex data symbols A0, ..., AN−1,which results in a sequence of complex time symbols a0, ..., aN−1 of the signal. Foreach symbol, after imaginary and real part separation, both parts are convertedto analogue in Digital-to-Analogue converter (D/A). Next, analogue signals arequadrature modulated (multiplied by cosine and sine functions) and summed upgiving the output modulated signal s(t).

24

1.6 Modulation

Figure 1.20: OFDM transmitter.

1.5.2 OFDM receiver

Figure 1.21 presents the simplified OFDM receiver model. Receiver is detecting thesignal rx(t). Besides the wanted signal also signal with 2f frequency is created.Therefore low pass filter is used to filter it out. Next, the signal is sampled andconverted to digital by the Analogue-to-Digital converter (A/D). The series of com-plex time symbols is then corrected for frequency drifts and global phase offsets (notshown in the diagram). In the next step FFT is carried out and frequency symboldetection takes place, which results in N parallel bit streams, joined finally into oneinitial bit stream s(i).

Figure 1.21: OFDM receiver.

1.6 Modulation

In telecommunications, modulation is the process of conveying a message signal, forexample digital information bit stream, inside another signal that can be physically

25

1 OFDMA principles

transmitted. Modulation of a sine waveform is used to transform a baseband messagesignal to a passband signal, for example a RF signal. Electrical signals can onlybe transferred over a limited passband frequency spectrum, with specific (non-zero)lower and upper cut-off frequencies. Modulating a sine wave carrier makes it possibleto keep the frequency content of the transferred signal as close as possible to thecentre frequency (typically the carrier frequency) of the passband.

For the purpose of LTE it is a good idea to think about the modulation as a tech-nique, which changes a digital signal of bits into another digital signal of complexnumbers. The complex numbers represent amplitude and phase shift of OFDMsubcarriers.

The modulation techniques used in LTE are based on phase and amplitude modu-lation of the carrier frequency, see also Figure 1.22:

• Binary Phase Shift Keying (BPSK) allows for transmission of one informationbit during one modulation symbol.

• Quadrature Phase Shift Keying (QPSK) allows for transmission of two infor-mation bits during one modulation symbol.

• 16 Quadrature Amplitude Modulation (16QAM) allows for transmission of 4information bits during one modulation symbol.

• 64 Quadrature Amplitude Modulation (64QAM) is the fastest modulation usedin LTE and allows for transmission of 6 information bits during one modulationsymbol.

Only QPSK, 16QAM and 64QAM are used in LTE for user data bit. QPSK is onlyused for some control information bits, which require robust modulation.

26

1.6 Modulation

Figure 1.22: LTE modulations.

27

1 OFDMA principles

28

2 EPS architecture

2.1 LTE requirements

Operators around the world have been rapidly deploying 3rd Generation (3G) net-work technologies, including UMTS, HSPA, and CDMA2000 1xEV-DO, to supportincreasing subscriber demand for mobile broadband services. LTE is a step towardthe 4th Generation (4G). LTE requirements are specified by TS 25.913:

• Capability-related requirements.

◦ Peak data rate.

Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) shouldsupport significantly increased instantaneous peak data rates. The sup-ported peak data rate should scale according to size of the spectrumallocation.

Note that the peak data rates may depend on the numbers of transmitand receive antennas at the UE. The targets for DL and UL peak datarates are specified in terms of a reference UE configuration comprising:

1. DL capability – 2 receive antennas at UE.

2. UL capability – 1 transmit antenna at UE.

For this baseline configuration, the system should support an instanta-neous downlink peak data rate of 100 Mbps within a 20 MHz downlinkspectrum allocation (5 bps/Hz) and an instantaneous uplink peak datarate of 50 Mbps (2.5 bps/Hz) within a 20 MHz uplink spectrum alloca-tion. The peak data rates should then scale linearly with the size of thespectrum allocation.

In case of spectrum shared between downlink and uplink transmission,E-UTRAN does not need to support the above instantaneous peak datarates simultaneously.

◦ Control Plane (CP) latency.

Transition time (excluding downlink paging delay and Non-Access Stra-tum (NAS) signalling delay) of less than 100 ms from a camped-state(Idle Mode) to an active state, in such a way that the User Plane (UP)is established.

◦ User Plane (UP) latency.

29

2 EPS architecture

E-UTRAN UP latency reduced to less than 5 ms in unload condition forsmall Internet Protocol (IP) packets.

◦ CP capacity.

The system should be able to support a large number of users per cellwith quasi instantaneous access to radio resources in the active state. Itis expected that at least 200 users per cell should be supported in theactive state for spectrum allocations up to 5 MHz, and at least 400 usersfor higher spectrum allocation.

A much higher number of users is expected to be supported in the campedstate.

• System performance requirements.

◦ DL user throughput.

Target for user throughput per MHz at the 5% point of the C.D.F.,2 to 3 times Release 6 HSDPA.

Target for averaged user throughput per MHz, 3 to 4 times Release 6HSDPA. Both targets should be achieved assuming Release 6 refer-ence performance is based on a single Tx antenna at the Node B withenhanced performance type 1 receiver in UE whilst the E-UTRA mayuse a maximum of 2 Tx antennas at the Node B and 2 Rx antennasat the UE.

The supported user throughput should scale with the spectrum band-width.

◦ UL user throughput.

Target for user throughput per MHz at the 5% point of the C.D.F.,2 to 3 times Release 6 Enhanced Uplink (deployed with a single Txantenna at the UE and 2 Rx antennas at the Node B).

Target for averaged user throughput per MHz, 2 to 3 times Release 6Enhanced Uplink (deployed with a single Tx antenna at the UE and2 Rx antennas at the Node B).

Both should be achievable by the E-UTRAN using a maximum ofa single Tx antenna at the UE and 2 Rx antennas at the Node B.Greater user throughput should be achievable using multiple Tx an-tennas at the UE.

The user throughput should scale with the spectrum bandwidth pro-vided that the maximum transmit power is also scaled.

◦ Spectrum efficiency.

Downlink.

In a loaded network, target for spectrum efficiency (bits/sec/Hz/site),3 to 4 times Release 6 HSDPA. This should be achieved assumingRelease 6 reference performance is based on a single Tx antenna atthe Node B with enhanced performance type 1 receiver in UE whilst

30

2.2 EPS architectural principles

the E-UTRA may use a maximum of 2 Tx antennas at the Node Band 2 Rx antennas at the UE.

Uplink

In a loaded network, target for spectrum efficiency (bits/sec/Hz/site),2 to 3 times Release 6 Enhanced Uplink (deployed with a single Txantenna at the UE and 2 Rx antennas at the Node B). This should beachievable by the E- UTRA using a maximum of a single Tx antennaat the UE and 2Rx antennas at the Node B.

◦ Mobility.

The E-UTRAN shall support mobility across the cellular network andshould be optimised for low mobile speed from 0 to 15 km/h. Highermobile speed between 15 and 120 km/h should be supported with highperformance. Mobility across the cellular network shall be maintained atspeeds from 120 km/h to 350 km/h (or even up to 500 km/h dependingon the frequency band).

◦ Coverage.

E-UTRAN should support the maximum cell range of 100 km.

2.2 EPS architectural principles

The LTE radio network is called E-UTRAN. System Architecture Evolution (SAE)is the core network architecture of the LTE wireless communication standard. SAEis the evolution of the GPRS Core Network. The main component of the SAEarchitecture is the Evolved Packet Core (EPC).

The Long Term Evolution/System Architecture Evolution (LTE/SAE) system, whichconsists of E-UTRAN and EPC, is called Evolved Packet System (EPS), see Figure2.1. LTE/SAE is specified from 3GPP Technical Specification (3GPP TS) Release8.

2.2.1 Evolved Packet Core (EPC)

The EPC provides access to external data networks (e.g., Internet, corporate net-works) and operator services (e.g., Multimedia Messaging Services (MMS)1, Multi-media Broadcast and Multicast Services (MBMS)2). It also performs functions re-lated to security (authentication, key agreement), subscriber information, chargingand inter-access mobility (GSM EDGE Radio Access Network (GERAN)/Univer-sal Terrestrial Radio Access Network (UTRAN)/E-UTRAN/Interworking Wireless

1Multimedia Messaging Services (MMS) is a standard way to send messages that include mul-timedia content to and from mobile phones. It extends the core SMS capability which only allowsexchange of text messages up to 160 characters in length. The most popular use of MMS is to sendphotographs from camera-equipped handsets, although it is also popular as a method of deliveringnews and entertainment content including videos, pictures, text pages and ringtones.

2Multimedia Broadcast and Multicast Services (MBMS) is a broadcasting service, which maybe offered via existing GSM and UMTS cellular networks. The main application is mobile TV. Theinfrastructure offers an option to use an uplink channel for interaction between the service and theuser.

31

2 EPS architecture

Figure 2.1: EPS architecture.

Local Area Network (IWLAN)/Code Division Multiple Access 2000 (CDMA2000)etc.). The EPC also tracks the mobility of inactive terminals (i.e., terminals inpower saving state).

The number of user plane nodes3 in the core network has been reduced from twoin Release 6 (Serving GPRS Support Node (SGSN) and Gateway GPRS SupportNode (GGSN)) to only one in EPS called Packet Data Network/Serving Gateway(P/S-GW). The P/S-GW can be divided into a S-GW and P-GW but often residesin the same physical node referred to as P/S-GW or System Architecture EvolutionGateway (SAE-GW). In typical implementations the P/S-GW is realised by softwareupgrade of GGSN.

The control plane node is called MME and it may be realised by software upgradeof SGSN.

2.2.2 Evolved UTRAN (E-UTRAN)

E-UTRAN performs all radio related functions for active terminals (i.e. terminalssending data). The number of user plane nodes in E-UTRAN has been reduced toone only and the node is called Evolved Node B (eNB) The interface between the

3User plane is a communication strata responsible for user data transmission, in contrast tocontrol plane, which is responsible for signalling transmission. The strata concept is explained inthe next section.

32

2.3 Strata

EPC and the E-UTRAN is called S1 and the interface between the eNBs is calledX2.

2.3 Strata

To keep the questions of mobility and connection management independent of theair interface technology, the concept of communication strata has been employed inUMTS and it is also used in LTE/SAE. The stack of protocols has been dividedinto:

• NAS – containing Core Network (CN) protocols between the CN and UE,which do not terminate in the E-UTRAN, but in the CN itself. E-UTRAN iscompletely transparent for these protocols, and hence they can be independentof the radio technology used.

• Access Stratum (AS) – containing radio access protocols between the UE andthe E-UTRAN. These protocols are different in GSM, UMTS and LTE, sincethe radio access technology is different here (OFDMA instead of TDMA orWCDMA).

2.3.1 Non-Access Stratum (NAS)

The concept of Non-Access Stratum (NAS) is almost the same as in UMTS, howeverit is implemented in much different way.

The UMTS uses the same mobility and connection management protocols as theearlier generation networks (GSM, GPRS) and they are the following:

• Connection Management (CM) and Mobility Management (MM) for the CSpart of the network,

• Session Management (SM) and GPRS Mobility Management (GMM) for thePS part.

The fact that LTE/SAE is totally packet oriented eliminates the protocols connectedwith the CS network part and modifies the NAS operation in PS part (i.e. the entirenetwork).

Consequently, the NAS in EPS:

• Introduces the new EPS Mobility Management (EMM) layer,

• Inherits the SM layer after UMTS.

From the changes presented above, one can deduct that lower layer EMM had tobe redefined for EPS to meet the requirements of the new concept of UE mobilityfor the PS transmission only. The SM remains the same due to the fact of commonway of handling the session management in LTE/SAE, UMTS and GSM (GPRS)systems.

The examples of functions performed by NAS:

• Mobility management for idle UEs,

• UE authentication,

33

2 EPS architecture

• EPS bearer management,

• Configuration and control of security,

• Paging initiation for idle UEs.

The NAS messages are transported by the Radio Resource Control (RRC) layer –the signalling layer of the AS. There are two ways to transport the NAS messagesby RRC, either by concatenating the NAS messages with other Radio ResourceControl (RRC) messages, or by including the NAS messages in dedicated RRCmessages without concatenation.

The NAS messages are protected using the ciphering and integrity protection servicesprovided by the Packet Data Convergence Protocol (PDCP) layer. However, NASis also protected by its own security functions terminated in the UE and MME,respectively.

On the network side, the NAS layers are in 3rd Generation Partnership Project(3GPP) agreed to be terminated by the MME.

The NAS state model is based on a two-dimensional model which consists of EMMstates describing the mobility management states that result from the mobility man-agement procedures e.g. attach and Tracking Area Update (TAU) procedures, andof EPS Connection Management (ECM) states describing the signalling connectivitybetween the UE and the EPC.

The ECM and EMM states are independent of each other and when the UE is inEMM-CONNECTED state this does not imply that the user plane (radio and S1bearers) is established.

2.3.2 Access Stratum (AS)

The services, access signalling, mobility and subscriber management specific to CNare completely outside the AS, and are transferred transparently through the Ra-dio Access Network (RAN). AS protocols are specific to the RAN being used bythe mobile system. This RAN may be implemented as the GSM Base Station Sys-tem (BSS), GERAN, UTRAN or E-UTRAN. AS provides radio access bearers forboth connection-oriented, packet-switched services and connectionless (store-and-forward) services. In LTE/SAE there is no CS network part thus the AS differssignificantly from the one in older technologies.

The AS provides the connectivity between the nodes in the E-UTRAN. There arethree interfaces that are involved in the AS concept:

• Radio interface – connectivity between the UE and the E-UTRAN node – theeNB.

• S1 – connectivity between eNB and the core network nodes:

◦ S1-MME – eNB and MME, responsible for control plane.

◦ S1-U – eNB and S-GW, responsible for user plane.

• X2 – connectivity between eNBs in E-UTRAN.

34

2.4 EPS Bearer and QoS

2.4 EPS Bearer and QoS

The EPS defines bearers for services and strictly binds them with QoS level provided.This strict mapping leads to definition of certain QoS level for certain applicationsusing the bearers in the network. Consequently, the bearers will always obtainappropriate QoS classes, according to the requirements of the service provided bythe application the UE utilises.

2.4.1 EPS Bearer

Similarly to UMTS, EPS implements a bearer concept for supporting end-user dataservices. The EPS bearer (similar to a Packet Data Protocol (PDP) context ofprevious 3GPP releases) is defined between the UE and the P-GW node in the EPC(which provides the end-users IP point of presence towards external networks), seeFigure 2.2.

Figure 2.2: EPS bearer concept.

End-to-end services (e.g. IP services) are multiplexed on different EPS Bearers.There is a many-to-one relation between end-to-end services and EPS Bearers. AnUL Traffic Flow Template (TFT) in the UE binds an Service Data Flow (SDF) toan EPS Bearer in the uplink direction. Multiple SDFs can be multiplexed onto thesame EPS Bearer by including multiple uplink packet filters in the UL TFT. ADL TFT in the P-GW binds an SDF to an EPS Bearer in the downlink direction.Multiple SDFs can be multiplexed onto the same EPS Bearer by including multipledownlink packet filters in the DL TFT.

The EPS Bearer is further sub-divided into a E-UTRAN Radio Access Bearer(E-RAB) and S5/S8 Bearer. An E-RAB transports the packets of an EPS Bearerbetween the UE and the EPC. When an E-RAB exists, there is a one-to-one map-ping between this E-RAB and an EPS Bearer. An S5/S8 Bearer transports thepackets of an EPS Bearer between a S-GW and a P-GW.

A Radio Bearer transports the packets of an EPS Bearer between a UE and aneNB. When a Radio Bearer exists, there is a one-to-one mapping between this

35

2 EPS architecture

Radio Bearer and the EPS Bearer/E-RAB. An S1 Bearer transports the packets ofan E-RAB between an eNB and a S-GW.

A UE stores a mapping between an uplink packet filter and a Radio Bearer tocreate the binding between an SDF and a Data Radio Bearer in the uplink. AP-GW stores a mapping between a downlink packet filter and an S5/S8a Bearer tocreate the binding between an SDF and an S5/S8a Bearer in the downlink.

An eNB stores a one-to-one mapping between a Radio Bearer and an S1 Bearer tocreate the binding between a Radio Bearer and an S1 Bearer in both the uplink anddownlink.

A S-GW stores a one-to-one mapping between an S1 Bearer and an S5/S8a Bearerto create the binding between an S1 Bearer and an S5/S8a Bearer in both the uplinkand downlink.

2.4.2 Quality of Service (QoS)

QoS concept

QoS has been defined by the International Telecommunication Union (ITU) as:

the collective effect of service performance, which determines the degree ofsatisfaction of a user of a service.

Thus, QoS is connected with the way the user perceives the service. The user isnot interested in how a service is provided but only whether or not he or she issatisfied with that service. So, from a user’s perspective the QoS level is a very sub-jective thing and if the network does not provide the desired level of satisfaction, theuser may simply stop using the service and possibly change to some other operatoroffering a similar service with the desired QoS level.

QoS classes

In UMTS four different QoS classes (referred also to as traffic classes) have beendefined. These QoS classes are:

• Conversational class,

• Streaming class,

• Interactive class, and

• Background class.

The main distinction between these QoS classes follows from how delay-sensitivethe traffic is: Conversational class is meant for traffic, which is very delay-sensitive,while Background class is the most delay-insensitive traffic class.

QoS Class Identifier (QCI)

In case of LTE, 3GPP in Release 8 introduces another concept: QoS Class Identifier(QCI). QCI is a scalar that is used as a reference to node specific parameters that

36

2.5 Integration with 2G and 3G

control packet forwarding treatment. They should be pre-configured by the operatorowning the node.

QCI values indicate the QoS characteristics for edge-to-edge packet forwarding be-tween UE and Policy and Charging Enforcement Function (PCEF). Each QCI isassociated with the following standardized performance characteristics:

• Resource Type (Guaranteed Bit Rate (GBR) or Non-GBR),

• Priority,

• Packet Delay Budget,

• Packet Error Loss Rate.

To control the edge-to-edge packet forwarding QCI is signaled to different networknodes while the above standardized characteristics are not. It is up to the operatorto map QCI values to the corresponding performance characteristics. The charac-teristics of QCI from 1 to 9 are standardized though and should be considered asguidelines when pre-configuring the node specific parameters. The goal of this op-eration is to ensure that applications mapped to a particular QCI receive the sameminimum level of QoS regardless access network they use (e.g. when UE is roamingor if the network operator uses equipment from different vendors).

Table 2.1 presents standardized QCI values mapped to the corresponding perfor-mance characteristics, as specified in 3GPP TS 23.203.

Mapping between QCI and QoS classes

In order to provide backward compatibility, the mapping between QCI and QoSclasses parameters was specified in Time Slot (TS) 23.401. It is presented in Table2.2.

2.5 Integration with 2G and 3G

When an E-UTRAN system is deployed in a network already supporting GERANand/or UTRAN it is possible to use a common core network for all accesses. Inpractice this means that the P-GW will provide GGSN functionality towards theexisting GPRS CN. Therefore an E-UTRAN/UTRAN/GERAN capable terminalwill not need to change the GGSN (i.e., the IP point of presence towards externalnetworks) when it changes Radio Access Technology (RAT)) and switches betweenGERAN, UTRAN or E-UTRAN. Figure 2.3 shows how the EPS inter-works withexisting 2nd Generation (2G)/3G networks. The figure presents the UTRAN whenutilizing the GPRS one tunnel approach standardized in 3GPP Release 7. Thisfeature makes it possible to bypass the SGSN in the user plane.

Figure 2.4 shows a standardization view on how GERAN, UTRAN and E-UTRANare integrated into the SAE. It should however be noted that the SGSN and MMEshares a lot of common functionality. It is also required that the CN protocols,SM and MM, used in 2G/3G are compatible with the respective protocols used inEPS meaning that the SGSN and MME share a common evolution in the 3GPPstandard. In a typical implementation/deployment view, it is likely that the 2G/3GSGSN and the MME are merged into one node, as illustrated in Figure 2.4. This

37

2 EPS architecture

QCIResource

typePriority

Packet

delay

budget

Packet

error

loss

rate

Example service

1

GBR

2 100 ms 10−2 Conversational voice

2 4 150 ms 10−3 Conversational video (livestreaming)

3 3 50 ms 10−3 Real-time gaming

4 5 300 ms 10−6 Non-conversational video(buffered streaming)

5

non-GBR

1 100 ms 10−6 IMS signalling

6 6 300 ms 10−6 Video bufferedstreaming,TCP basedservices (e.g. www, e-mail,chat, ftp, p2p file sharing,progressive video, etc.)

7 7 100 ms 10−3 Voice, video live streaming,interactive gaming

8 8 300 ms 10−6 ”Premium bearer” for videobuffered streaming, TCPbased services (e.g. www,e-mail, chat, ftp, p2p filesharing, progressive video,etc) for premium subscribers

9 9 300 ms 10−6 ”Default bearer” for video,TCP based services (etc. fornon-privilaged subscribers

Table 2.1: QoS Class Identifier (QCI) defined for LTE/SAE.

QCI Traffic class

Traffic

Handling

Priority

Signalling

indication

Source statistics

descriptor

1 Conversational N/A N/A Speech

2 Conversational N/A N/A Unknown

3 Conversational N/A N/A Unknown

4 Streaming N/A N/A Unknown

5 Interactive 1 Yes N/A

6 Interactive 1 No N/A



9 Background N/A N/A N/A

Table 2.2: Mapping between standardized QCIs and pre-Relese-8 QoS parametervalues.

38

2.6 Interfaces overview

Figure 2.3: E-UTRAN, UTRAN and GERAN architecture. GPRS one tunnelapproach.

will make it possible to support intra SGSN/MME and inter P/S-GW/GGSN nodemobility between the different accesses.


This section contains a brief overview of the LTE/SAE interfaces.

Gi

Gi is the interface to external packet data networks (e.g. Internet) and contains theend-user’s IP Point of Presence (PoP). All user-plane and control-plane functionsthat use the Gi interface are handled above the end-user’s IP layer, whereas allterminal mobility within 3GPP is handled below the Gi interface.

S1

S1 is the interface between eNB and MME and between eNB and S-GW. In the userplane this interface will be based on GTP User data tunnelling (GTP-U) (similarto Iu and Gn interface in UMTS). In the control plane the interface is more similar

39

2 EPS architecture

Figure 2.4: Typical implementation of LTE/SAE. Combined SGSN/MME onetunnel approach.

to RAN Application Part (RANAP), with some simplifications and changes due tothe different functional split and mobility within EPS.

It has been agreed to split the S1 interface into a S1-CP (control plane) and S1-UP (user plane) part. The signalling transport on S1-CP will be based on StreamControl Transmission Protocol (SCTP). The signalling protocol for S1 is called S1Application Protocol (S1AP). S1AP protocol has the following functions:

• EPS Bearer management function.

This overall functionality is responsible for setting up, modifying and releasingEPS bearers, which are triggered by the MME The release of EPS bearers maybe triggered by the eNB as well.

• Initial context transfer function.

This functionality is used to establish an S1 UE context in the eNB, to setupthe default IP connectivity, to setup one or more SAE bearer(s) if requestedby the MME, and to transfer NAS signalling related information to the eNBif needed.

• Mobility functions for UEs in LTE ACTIVE in order to enable:

◦ a change of eNB within LTE/SAE (inter MME/S-GW handovers) via the

40


S1 interface (with EPC involvement),

◦ a change of RAN nodes between different RAT (inter-3GPP-RAT han-dovers) via the S1 interface (with EPC involvement).

• Paging.

This functionality provides the EPC the capability to page the UE.

• S1 interface management functions:

◦ Reset functionality to ensure a well defined initialisation on the S1 inter-face.

◦ Error Indication functionality to allow a proper error reporting/handlingin cases where no failure messages are defined.

◦ Overload function to indicate the load situation in the control plane ofthe S1 interface.

• NAS signaling transport function between the UE and the MME is usedto:

◦ transfer NAS signalling related information and to establish the S1 UEcontext in the eNB,

◦ transfer NAS signalling related information when the S1 UE context inthe eNB is already established.

• S1 UE context release function.

This functionality is responsible to manage the release of UE specific contextin the eNB and the MME.

S1 is a many-to-many interface.

X2

X2 is the interface between eNBs. The interface is mainly used to support activemode UE mobility (Packet Forwarding). This interface may also be used for multi-cell Radio Resource Management (RRM) functions. The X2-CP interface consistsof a signalling protocol called X2 Application Protocol (X2AP) on top of SCTP.The X2-UP interface is based on GTP-U. The X2-UP interface is used to supportloss-less mobility (packet forwarding).

The X2-AP protocol provides the following functions:

• Mobility Management (MM).

This function allows the eNB to move the responsibility of a certain UE toanother eNB. Forwarding of user plane data is a part of the mobility manage-ment.

• Load management.

This function allows eNBs to indicate overload and traffic load to each other.

• Reporting of general error situations.

41

2 EPS architecture

This function allows reporting of general error situations, for which functionspecific error messages have not been defined.

The X2 interface is a many-to-many interface.

S3

S3 is a control interface between the MME and 2G/3G SGSNs. The interface isbased on Gn/GTP Control plane (GTP-C) (SGSN-SGSN), possibly with some newfunctionality to support signalling free idle mode mobility between E-UTRAN andUTRAN/GERAN. S3 will not support packet forwarding; instead this will be sup-ported on the S4 interface.


The S3 interface is similar to the S10 interface between MMEs which will be usedfor intra-LTE mobility between two MME pool areas.

S4

S4 is the interface between the P-GW and 2G/3G SGSNs. The interface is basedon Gn/GPRS Tunnelling Protocol (GTP) (SGSN-GGSN). The user plane interfaceis based on GTP-U (same as S1-UP and Iu-UP) and the control plane is based onGTP-C (similar to S11).


The S4 interface is backwards compatible with the Gn interface.

S6

S6a enables transfer of subscription and authentication data for authenticating/au-thorizing user access to the evolved system (Authentication, authorisation and ac-counting (AAA) interface) between MME and Home Subscriber Server (HSS). S6dis between the SGSN and the HSS. S6 is based on Diameter.

S5/S8

S5/S8 is the interface between the S-GW and P-GW. In principle S5 and S8 is thesame interface, the difference being that S8 is used when roaming between differentoperators while S5 is network internal. The S5/S8 interface will exist in two variantsone based on Gn/GTP (SGSN-GGSN) and the other will use the Internet Engineer-ing Task Force (IETF) specified Proxy Mobile IP (PMIP) for mobility control withadditional mechanism to handle QoS.

The usage of PMIP or GTP on S5/S8 will not be visible over the S1 interface orin the terminal. In the non roaming case the S-GW and P-GW functions can beperformed in one physical node.

It has been agreed in 3GPP that the usage of PMIP or GTP on S5 and S8 shouldnot impact RAN behaviour or impact the terminals.

42


In the roaming case S8 is providing user and control plane between the S-GW in theVisited PLMN (VPLMN) and the P-GW in the Home PLMN (HPLMN). S8 is theinter Public Land Mobile Network (PLMN) variant of S5.

S5/S8 is a many-to-many interface.

S9

S9 provides transfer of QoS policy and charging control information between theHome Policy and Charging Rules Function (PCRF) and the Visited PCRF in orderto support local breakout function.

S10

S10 is a control interface between the MMEs which will be very similar to theS3 interface between the SGSN and MME. The interface is based on Gn/GTP-C(SGSN-SGSN) with additional functionality.


S11

S11 is the interface between the MME and S-GW. The interface is based onGn/GTP-C (interface between SGSN and GGSN) with some additional functions forpaging coordination, mobility compared to the legacy Gn/GTP-C (SGSN-GGSN)interface.


S12

S12 is the interface between UTRAN and S-GW for user plane tunnelling whendirect tunnel is established. It is based on the Iu-u/Gn-u reference point using theGTP-U protocol as defined between SGSN and UTRAN or respectively betweenSGSN and GGSN. Usage of S12 is an operator configuration option.

S13

S13 enables UE identity check procedure between MME and Equipment IdentifyRegister (EIR).

SGi

SGi is the interface between the P-GW and the packet data network. Packet datanetwork may be an operator external public or private packet data network or anintra operator packet data network, e.g. for provision of IP Multimedia Subsystem(IMS) services. This interface corresponds to Gi for 3GPP accesses.

Rx

Rx is the interface between the application server and the PCRF

43

2 EPS architecture

Gx

Gx provides transfer of QoS policy and charging rules from PCRF to PCEF in theP-GW.

2.7 Evolved Packet Core (EPC) functions

EPC is the core network of the SAE system and is built up with P/S-GW nodes,together with MME nodes.

2.7.1 Mobility Management Entity node

The EPS architecture defines MME node, which contains core network control func-tionality. Although the functionality is not entirely the same, the MME conceptuallyconstitutes a control plane SGSN node. The CP terminal protocols terminate at theMME, which also manages the mobility contexts of the UEs. The same MME re-mains in control of a UE as long as the UE moves within an MME pool area.

The MME handles the mobility and session management functions listed below:

• UE attach/detach handling.

This allows UE to register and de-register to the network.

• Security.

The MME implements functions for Authentication and Authorization to ver-ify users’ identities, grant access to the network and track users’ activities,respectively. In addition, the MME performs ciphering and integrity protec-tion of NAS message signalling.

• EPS Bearer handling.

The MME manages the setting up, modification and tearing down of EPSBearers. It is assumed that a UE in E-UTRAN will always have one defaultEPS Bearer established at the time of attachment to the network.

• MM for idle mode UEs.

The MME manages mobility of idle mode UEs. Idle mode UEs are trackedwith the granularity of Tracking Areas (TAs).

2.7.2 P-GW and S-GW nodes

The EPS architecture defines the Packet Data Network/Serving Gateway (P/S-GW)node. The P/S-GW is the anchor point for the user plane for a terminal movingbetween eNBs. The S-GW is only changed when the UE move to a new S-GWpool area while the P-GW is normally kept as long as the UE is attached to thenetwork.

The P/S-GW functionality is very similar to the existing GGSN node. The mainadditions are adding support for packet buffering during E-UTRAN paging andadditional support for Non-3GPP interworking (e.g. CDMA2000, WLAN). The

44

2.7 Evolved Packet Core (EPC) functions

P-GW provides an interface to the outside world (e.g. the Internet). The P/S-GWcan mainly be seen as a user plane node, however it also performs some QoS relatedsignalling (it terminates the interface for policy control).

The P/S-GW is involved in the following control plane functions:

• EPS Bearer Handling.

The P/S-GW triggers the setup of EPS Bearers upon request from the policycontrol functions.

• Mobility Anchor – IP PoP.

The P-GW acts as a mobility anchor point which hides UE mobility from thefixed network. When a UE attaches to the network it is assigned an IP addressfrom a P-GW, which then also assumes the role of mobility anchor to the UE.While the control of a UE may be transferred to another MME or S-GW as aconsequence of a Handover (HO), the UE’s IP PoP will remain at the P-GW.Thus, the mobility of UEss is transparent to the fixed network.

Further, the P/S-GW handles the following user plane functions:

• QoS Policy Control and Enforcement.

To simplify bearer requests from an application point of view, increase op-erator’s control over its network resources and limit the potential for abuseby users, EPS QoS is network controlled. The policy control and enforcementfunctions associate users’ traffic flows with appropriate QoS classes and executerate policing to prohibit users or flows from exceeding the QoS limits speci-fied in users’ subscription agreements. DL traffic is policed in the P/S-GWwhereas UL traffic is policed in the eNB.

• Charging.

The charging function is responsible for charging the user for its traffic accord-ing to the rate that applies for a particular service, subscription etc.

• Lawful Intercept.

This function enables communications to be electronically intercepted, or eaves-dropped, by law enforcement agencies, should it be authorized by judicial orregulatory mandates.

2.7.3 MME and S-GW pooling concept

It is possible to pool a number of MME and S-GW nodes together in order to elimi-nate the risk that one node failure will cause parts of the network to be out of service.This is possible since there is a many-to-many relation interface between eNBs andEPC nodes where each eNB is associated with a set of MMEs and S-GWs calledan MME and S-GW pool. The resulting network is non-hierarchical. Independentpooling of MME and S-GW are supported, it is however not possible to change aS-GW without involving the MME.

An operator may pool MMEs and S-GWs into one or several pools depending onorganisation, regulatory requirements, transport providers etc. This is illustrated inFigure 2.5. The flexibility of the pooling concept makes it possible to enable partial

45

2 EPS architecture

sharing of networks; i.e., to use only a part of the operator’s network as a sharednetwork.

Figure 2.5: Inter-pool mobility.

The individual pooled MMEs and S-GW do not have to be located on the samephysical site, but can be distributed in the network. All pools of a particular op-erator are assumed to be interconnected by means of an interface similar to theS3/S4/S10/S11 interface.

When a UE attaches to the network, it is assigned to one of the MMEs that belongto the MME pool associated with the eNB through which the UE is attaching, theMME then selects an S-GW in the S-GW pool. No change of MME or S-GW isrequired while the UE moves around among eNBs belonging to the same MME orS-GW pool. If the UE moves out of the pools coverage it is reassigned to an MMEor S-GW in the pool associated with the new eNB.

The P-GW, which performs charging, policy enforcement and UE’s IP PoP is notchanged when the S-GW is relocated. The main purpose of the S-GW is to act asa local mobility anchor and to buffer packets during E-UTRAN paging. In someequipment vendors views (for example Ericsson) S-GWs are rare and in most casesthe S-GW and P-GW functions are performed by the same physical node. MMErelocation may be more motivated since there may be limits on how many eNBs theMME is connected to.

46

2.8 LTE functions

Partially overlapping pools will also be supported. Overlapping pools may havesome benefits since it makes it possible to avoid some of the negative effects of hardpool borders, however it comes with extra complexity.

2.8 LTE functions

LTE is a synonym for the new system’s radio access network, which officially isreferred to in 3GPP specifications as E-UTRAN. This radio network is functionallyan evolution of the 3G UTRAN, although the radio transmission technology hasbeen changed completely.

2.8.1 LTE general principles

The radio interface in LTE is developed according to the requirements of spectrumflexibility, spectrum efficiency, cost effectiveness etc. Robustness against time disper-sion has influenced the choice of transmission technique in both UL and DL.

Spectrum flexibility incorporates the possibility to use both paired and unpairedspectrum, i.e. LTE should support both FDD and TDD based duplex arrangements,respectively. Also, the support for operation in six different bandwidths, 1.4, 3,5, 10, 15 and 20 MHz, plays an important role of the spectrum flexibility partin the standardisation of the radio interface. Actually, the LTE radio interfaceimplementation supports operation in any bandwidth between 1.4 and 20 MHz insteps of one resource block, which corresponds to 12 subcarriers or 180 kHz.

High spectrum efficiency is achieved by the use of higher order modulation schemes,like 16QAM and 64QAM and advanced antenna solutions, including transmit andreceive diversity, beamforming and spatial multiplexing (MIMO).

Furthermore, the ISI is reduced by the choice of OFDM in the DL and Single CarrierFrequency Division Multiple Access (SC-FDMA) in UL. Both of these methodsresults in a long symbol time and thus a reduced ISI, which increases the performancein highly time-dispersive radio environments.

The UL and DL has a similar time-domain structure.

2.8.2 eNB functionality

E-UTRAN consists solely of the eNB, which is responsible for all radio interfacefunctionality.

eNB is the RAN node in the EPS architecture that is responsible for radio transmis-sion to and reception from UEs in one or more cells. The eNB is connected to EPCnodes by means of an S1 interface. The eNB is also connected to its neighbour eNBsby means of the X2 interface. Some significant changes have been made to the eNBfunctional allocation compared to UTRAN. Most Release 6 Radio Network Con-troller (RNC) functionality has been moved to the E-UTRAN eNB. Below followsa description of the functionality provided by eNB.

• Cell control and MME pool support.

47

2 EPS architecture

eNB owns and controls the radio resources of its own cells. Cell resources arerequested by and granted to MMEs in an ordered fashion. This arrangementsupports the MME pooling concept. S-GW pooling is managed by the MMEsand is not really seen in the eNB.

• Mobility control.

The eNB is responsible for controlling the mobility for terminals in active state.This is done by ordering the UE to perform measurement and then performinghandover when necessary.

• Control Plane (CP) and User Plane (UP) security.

The ciphering of user plane data over the radio interface is terminated inthe eNB. Also the ciphering and integrity protection of RRC signalling isterminated in the eNB.

• Shared channel handling.

Since the eNB owns the cell resources, the eNB also handles the shared andrandom access channels used for signalling and initial access.

• Segmentation/concatenation.

Radio Link Control (RLC) Service Data Units (SDUs) received from the PDCPlayer consist of whole IP packets and may be larger than the transport blocksize provided by the physical layer. Thus, the RLC layer must support seg-mentation and concatenation to adapt the payload to the transport block size.

• Hybrid Automatic Repeat reQuest (HARQ).

Medium Access Control (MAC) HARQ layer with fast feedback provides ameans for quickly correcting most errors from the radio channel. To achievelow delay and efficient use of radio resources, the HARQ operates with anative error rate which is sufficient only for services with moderate error raterequirements such as for instance Voice over IP (VoIP). Lower error rates areachieved by letting an outer Automatic Repeat reQuest (ARQ) layer in theeNB handle the HARQ errors.

• Scheduling.

Scheduling with support for QoS provides for efficient scheduling of UP andCP data.

• Multiplexing and mapping.

The eNB performs mapping of logical channels onto transport channels.

• Physical layer functionality.

The eNB handles the physical layer processing such as scrambling, Transmit(TX) diversity, beamforming and OFDM modulation. The eNB also handleslayer one functions like link adaptation and power control.

• Measurements and reporting.

eNB provides functions for configuring and making measurements on the radioenvironment and eNB-internal variables and conditions. The collected data is

48

2.8 LTE functions

used internally for RRM but can be reported for the purpose of multi-cellRRM.

49

2 EPS architecture

50

3 LTE signalling

3.1 User plane

The protocols performing the user plane functions in the radio interface are asfollows:

• Packet Data Convergence Protocol (PDCP), which maps the EPS beareronto the E-UTRAN radio bearer and performs Robust Header Compression(ROHC).

• Radio Link Control (RLC), which maps the E-UTRAN radio bearer to alogical channel and performs segmentation, in-sequence delivery and retrans-missions.

• Medium Access Control (MAC), which maps the logical channel to atransport channel and is responsible for HARQ and scheduling.

• The physical layer, which maps the transport channel onto a physical chan-nel and performs channel coding, modulation etc.

The LTE radio interface protocol architecture for User Plane is shown in Figure 3.1.

Figure 3.1: User plane for LTE.

51

3 LTE signalling

3.2 Control plane

The protocols performing the control plane functions in the radio interface are asfollows:

• RRC protocol, which is used to transfer the NAS information over the radiointerface.

• PDCP.

• RLC.

• MAC.

• The physical layer.

The Figure 3.2 presents the LTE radio interface protocol architecture for the controlplane.

Figure 3.2: Control plane for LTE.

3.3 Protocols

3.3.1 Radio Resource Control (RRC)

The following control plane functions are agreed in 3GPP to be performed by theRadio Resource Control (RRC) layer:

• Broadcast of System Information (SI) related to the NAS,

• Broadcast of SI related to the AS,

• Paging,

• Establishment, maintenance and release of an RRC connection between theUE and E-UTRAN including:

◦ Allocation of temporary identifiers between UE and E-UTRAN,

52

3.3 Protocols

◦ Configuration of radio resources for RRC connection including SignallingRadio Bearer (SRB),

• Establishment, maintenance and release of point to point radio bearers,

• Mobility functions including:

◦ UE measurement reporting and control of the reporting for inter-cell andInter Radio Access Technology (Inter-RAT) mobility,

◦ Inter-cell handover,

◦ UE cell selection and reselection and control of cell selection and reselec-tion,

◦ UE context transfer between eNBs,

• Notification for MBMS services,

• Establishment, configuration, maintenance and release of radio bearers forMBMS services,

• QoS management functions. (Note: These functions are spread across multiplelayers),

• UE measurement reporting and control of the reporting,

• MBMS control,

• NAS direct message transfer to/from NAS from/to UE.

On the network side, the RRC layer is terminated by the eNB.

RRC specification aspects

The RRC specification includes a hierarchy of procedures, where the highest level iscalled ”High-level procedures” covering e.g. Broadcast Control Channel (BCCH) ac-quisition, paging, RRC connection establishment, reestablishment, re-configurationand release. The content of high level procedure messages may then trigger Elemen-tary Procedures that execute e.g. measurement, radio resource or security configu-ration. Mobility is also described as an elementary procedure. A single high-levelprocedure may in some cases trigger multiple elementary procedures.

Relation between NAS and AS

The relation between NAS and AS states is characterised by the following principles,which is also illustrated in Figure 3.3.

• EMM-Deregistered & ECM-Idle ⇒ RRC IDLE:

◦ Mobility: PLMN selection,

◦ UE position: not known by the network.

• EMM-Registered & ECM-Idle ⇒ RRC IDLE:

◦ Mobility: cell reselection,

◦ UE position: known by MME at tracking area level.

53

3 LTE signalling

Figure 3.3: Relation between NAS and AS.

• EMM-Registered & ECM-Connected with radio bearers established ⇒RRC CONNECTED:

◦ Mobility: handover,

◦ UE position: known by the network at cell level.

3.3.2 Packet Data Convergence Protocol (PDCP)

Packet Data Convergence Protocol (PDCP) provides its services to the NAS/RRC atthe UE or the relay at the eNB. The PDCP supports the following functions:

• Header compression and decompression of IP data flows using the ROHC pro-tocol, at the transmitting and receiving entity, respectively.

• Transfer of data (user plane or control plane). This function is used for con-veyance of data between users of PDCP services.

• Maintenance of PDCP sequence numbers for radio bearers mapped on RLCacknowledged mode.

• In-sequence delivery of upper layer Packet Data Units (PDUs) at handover.

• Duplicate elimination of lower layer SDUs at handover for radio bearers mappedon RLC acknowledged mode.

• Ciphering and deciphering of user plane data and control plane data

• Integrity protection of control plane data.

• Timer based discard.

PDCP uses the services provided by the RRLC sublayer.

54

3.3 Protocols

3.3.3 Radio Link Control (RLC)

The Radio Link Control (RLC) protocol supports an Unacknowledged Mode (UM)and an Acknowledged Mode (AM). Whether UM or AM is used is configured perradio bearer. For example, UM could be used for VoIP while AM is used to carryTransmission Control Protocol (TCP)-based traffic. An RLC transparent modeexists as well, but it shall be only used to send RRC messages when no RLC UM orAM entity is set up, yet.

The RLC layer supports segmentation and concatenation of RLC SDUs. Dependingon the scheduler decision, a certain amount of data is selected from the RLC SDUbuffer and segmented and/or concatenated depending on the size of the SDUs. Thisselected data block becomes the RLC PDU to which a sequence number is assigned.This means that one transport block contains only a single RLC PDU per radiobearer except if an RLC retransmission is required. In this case an RLC PDUcontaining new data might be multiplexed at the MAC layer with an RLC PDUretransmission. In order to allow the RLC SDU reassembly at the receiver, theRLC header carries the required segmentation, re-segmentation and concatenationinformation. The RLC sequence number will also be used at the receiver for in-sequence delivery to the RLC SDU reassembly entity.

In AM, RLC is responsible for correcting residual HARQ errors by operating anotherARQ protocol since it would be expensive in terms of transmit power to reach therequired residual error rates of 10−5 or less in the MAC HARQ protocol.

The ARQ retransmission units are RLC PDUs or RLC PDU segments. If an RLCretransmission is required and the radio quality has changed significantly com-pared to the original RLC transmission, the RLC protocol is able to perform are-segmentation. In this case RLC segments a PDU into smaller PDU segments.The number of RLC re-segmentations of an RLC PDU is unlimited.

RLC performs reordering of received RLC PDUs and PDU segments in order toensure that RLC SDUs are delivered in sequence to higher layers.

Retransmissions are initiated either by status reports sent by the RLC receiver or bylocal triggers from MAC layer in case of reaching the maximum number of HARQtransmissions. Status Reports are triggered either by polls sent from the RLCsender or by detecting missing PDUs after the PDUs have passed the reorderingentity. Similar to UTRAN, the LTE RLC supports a status prohibit timer and apoll timer.

Finally, RLC provides means for protocol error detection and recovery (e.g. reset)and duplicate detection.

3.3.4 Medium Access Control (MAC)

The Medium Access Control (MAC) layer for the LTE access can be comparedto the Release 6 MAC-hs/MAC-e and covers mainly similar functionality: HARQ,priority handling (scheduling), transport format selection and Discontinuous Recep-tion (DRX) control (not part of MAC in Release 6).

The HARQ protocol is very similar to the solution adopted for High Speed Down-link Packet Access (HSDPA), i.e., the protocol uses multiple stop-and-wait hybrid

55

3 LTE signalling

ARQ processes. The motivation for this type of protocol is to allow continuoustransmission, which cannot be achieved with a single stop-and-wait scheme, whileat the same time having some of the simplicity of a stop-and-wait protocol. Thefunctionality and performance is similar to that of a window based selective repeatprotocol but only single-bit HARQ feedback is required.

The protocol is modelled as a number of parallel HARQ processes, where eachprocess uses a simple stop-and-wait protocol. By using NHARQ parallel HARQprocesses, where NHARQ > Round trip time/Subframe length, a continuous trans-mission is achieved. The maximum UE processing time before sending a HARQfeedback has been specified such that 8 HARQ processes are needed for continuoustransmission in FDD with a typical eNB implementation.

In 3GPP, the current working assumption is to use a synchronous HARQ for theuplink and an asynchronous HARQ for the downlink. That is, for the uplink, thesubframe when the retransmission occurs is known at the receiver, while for thedownlink the scheduler has the freedom to choose the subframe for the retransmis-sion dynamically. For both up- and downlink a synchronous, single-bit HARQ feed-back Acknowledge (ACK)/Negative Acknowledge (NACK) is sent providing feed-back about the success of the previous transmission. The HARQ protocol is adap-tive in both uplink and downlink, meaning that the scheduler can decide to use adifferent resource for a retransmission compared to that one used for the previous(re)transmission.

The redundancy version of a (re)transmission needs to be known by the receiver.Thus, the redundancy version and an indication whether the transmission contains afirst transmission or a retransmission is indicated on the Physical Downlink ControlChannel (PDCCH). In case the data is a retransmission of previously stored data,the received data is soft combined with the data stored in the soft buffer. In casethe received data is not a retransmission or a retransmission of data that has notbeen stored, the soft buffer is cleared and only the latest received data is placed inthe buffer.

The Figure 3.4 presents the principle of HARQ operation for MAC layer.

Figure 3.4: HARQ principle - four multiple HARQ processes.

The MAC layer does not support in-order delivery to RLC. HARQ retransmissionswill lead to that MAC PDUs are received in a different order than they were sent.Due to the lack of MAC sequence numbers it is up to the RLC receivers to restorethe original sequence and to provide in-order delivery to higher layers.

56

3.4 Radio interface structure

The MAC layer supports the ARQ in the RLC layer with certain triggers if residualHARQ errors are detected, e.g., if the maximum number of HARQ transmissionshas been reached. Finally, MAC also allows flows from a single user to be multi-plexed. Correspondingly, the MAC header carries multiplexing information used tode-multiplex RLC PDUs to different flows.

3.4 Radio interface structure

The radio interface is structured in a layered model, similar to WCDMA, witha layer 2 bearer (here called EPS Bearer Service), which corresponds to a PDP-context in Release 6, carrying layer 3 data and the end-to-end service. The EPSbearer is carried by the E-UTRAN Radio Bearer Service in the radio interface. TheE-UTRAN radio bearer is carried by the radio channels. The radio channel structureis divided into logical, transport and physical channels. The logical channels arecarried by transport channels, which in turn are carried by the physical channels asillustrated in Figure 3.5.

57

3 LTE signalling

Figure 3.5: LTE radio interface structure for DL.

58

4 LTE radio interface introduc-tion

4.1 Channel structure

The physical layer provides transport channels to the L2. These transport channelsdiffer in their characteristics how data is transmitted and are mapped to differentlogical channels provided by the MAC layer. Logical channels describe which typeof data is conveyed.

4.1.1 Logical channels

The logical channels can be divided into control channels and traffic channels. Thecontrol channels are used for transfer of control plane information and the trafficchannels are used for the transfer of user plane information. The following logicalchannels are supported for LTE:

• Control channels:

◦ Broadcast Control Channel (BCCH).A downlink channel for broadcasting system control information.

◦ Paging Control Channel (PCCH).A downlink channel that transfers paging information. This channel isused when the network does not know the location cell of the UE.

◦ Common Control Channel (CCCH).This channel is used by the UEs having no RRC connection with thenetwork. CCCH would be used by the UEs when accessing a new cell orafter cell reselection.

◦ Multicast Control Channel (MCCH).A point-to-multipoint downlink channel used for transmitting MBMSscheduling and control information from the network to the UE, for oneor several Multicast Traffic Channels (MTCHs). After establishing anRRC connection this channel is only used by UEs that receive MBMS.

◦ Dedicated Control Channel (DCCH).A point-to-point bidirectional channel that transmits dedicated controlinformation between a UE and the network. Used by UEs having an RRCconnection.

59

4 LTE radio interface introduction

• Traffic channels:

◦ Dedicated Traffic Channel (DTCH).A DTCH is a point-to-point channel, dedicated to one UE, for the transferof user information. A DTCH can exist in both uplink and downlink.

◦ Multicast Traffic Channel (MTCH).A point-to-multipoint downlink channel for transmitting traffic data fromthe network to the UE using MBMS.

4.1.2 Transport channels

An effort has been made to keep a low number of transport channels in order toavoid unnecessary switches between different channel types, which are found to betime consuming in UMTS. In fact there is currently only one transport channelin downlink and one in uplink carrying user data, i.e., channel switching is notneeded.

For LTE, the following transport channels are provided by the physical layer:

• Downlink:

◦ Broadcast Channel (BCH).A low fixed bit rate channel broadcast in the entire coverage area of thecell. Beamforming is not applied.

◦ Downlink Shared Channel (DL-SCH).A channel with possibility to use HARQ and link adaptation by varyingthe modulation, coding and transmit power. The channel is possible tobroadcast in the entire cell and beamforming may be applied. UE powersaving (DRX) is supported to reduce the UE power consumption. MBMStransmission is also supported.

◦ Paging Channel (PCH).A channel that is broadcast in the entire cell. DRX is supported to enablepower saving.

◦ Multicast Channel (MCH).A separate transport channel for multicast MBMS. This channel is broad-cast in the entire coverage area of the cell. Combining of MBMS trans-missions from multiple cells Multicast Broadcast Single Frequency Net-work (MBSFN) is supported.

• Uplink:

◦ Uplink Shared Channel (UL-SCH).A channel with possibility to use HARQ and link adaptation by vary-ing the transmit power, modulation and coding. Beamforming may beapplied.

◦ Random Access Channel (RACH).A channel used to obtain timing synchronization (asynchronous randomaccess) and to transmit information needed to obtain scheduling grants(synchronous random access). The transmission is typically contention

60

4.1 Channel structure

based. For UEs having an RRC connection there is some limited supportfor contention free access.

4.1.3 Physical channels

The physical layer offers services to the MAC layer in the form of transport channels.User data to be transmitted is delivered to the physical layer from the MAC layer inthe form of transport blocks. The MAC layer at the transmitter side also provides thephysical layer with control information necessary for transmission and/or receptionof the user data.

The physical layer defines physical channels and physical signals.

• A physical channel corresponds to a set of physical resources used for trans-mission of data and/or control information from the MAC layer.

• A physical signal, which also corresponds to a set of physical resources, is usedto support physical-layer functionality but does not carry any information fromthe MAC layer.

From a specification perspective, the interface between 3GPP TS 36.211 and 36.212is defined in terms of physical channels, while physical signals are generated inside36.211. Figure 4.1 illustrates the logical channels and their mapping to transportchannels and physical channels.

• Physical channels:

◦ Physical Downlink Shared Channel (PDSCH).Transmission of the DL-SCH transport channel.

◦ Physical Uplink Shared Channel (PUSCH).Transmission of the UL-SCH transport channel.

◦ Physical Control Format Indicator Channel (PCFICH).Indicates the PDCCH format.

◦ Physical Downlink Control Channel (PDCCH).DL Layer 1 (L1)/Layer 2 (L2) control signalling.

◦ Physical Uplink Control Channel (PUCCH).UL L1/L2 control signalling.

◦ Physical Hybrid ARQ Indicator Channel (PHICH).Carries DL HARQ ACK/NACK.

◦ Physical Broadcast Channel (PBCH).DL transmission of the BCH transport channel.

◦ Physical Multicast Channel (PMCH).DL transmission of the MCH transport channel.

◦ Physical Random Access Channel (PRACH).UL transmission of the random access preamble as given by the RACHtransport channel.

• Physical signals:

61


Figure 4.1: LTE channels mapping.

62

4.2 Time domain structure

◦ Reference Signals (RS).Support measurements (for example for cell selection process) and coher-ent demodulation. Transmitted in both downlink and uplink.

◦ Primary Synchronisation Signals (P-SS) and Secondary Syn-chronisation Signals (S-SS).They are transmitted in the downlink and used in the cell search proce-dure. They transmit a parameter, which is used to identify a cell on theair interface. P-SS transmits a cell parameter physicalLayerSubCellId ={0, 1, 2}. S-SS transmits a cell parameter physicalLayerCellIdGroup ={0, 1, ....167}. The two parameters together indicated the CellID accord-ing the below formula:

CellID = 3 · physicalLayerCellIdGroup+ physicalLayerSubCellId

(4.1)

◦ Sounding Reference Signal (SRS).Supports UL channel quality measurements for scheduling purpose. Trans-mitted in UL in wide frequency band to let the eNB discover and allocatethe best subcarriers for UL PUSCH.

4.2 Time domain structure

4.2.1 FDD

For the LTE FDD mode of operation, the time domain structure is divided into 10ms long radio frames. Each radio frame consists of ten equally sized subframes of1 ms length, which is illustrated in Figure 4.2. Each subframe, in turn, consists oftwo equally sized slots of 0.5 ms length. The subframe is the typical scheduling unitof LTE, while slots are relevant in case of frequency hopping. Figure 4.2 is valid forboth the downlink and uplink transmission direction.

As a result of OFDMA and applied subcarrier spacing of 15 kHz, the length of theOFDMA symbol is 1

15 kHz = 66.67µs. To the beginning of each OFDM symbol, acyclic prefix is appended, which is a guard time to combat ISI due to multipath prop-agation. Cyclic prefix is a copy of the ending part of the OFDM symbol and whenit is appended to the beginning of the OFDM symbol then the frequency domaincontent of the transmitted signal is unchanged, see Figure 4.3 and Figure 1.18. Withcyclic prefix the transmission of time domain signal takes longer, but when receivermakes FFT of the received time domain signal then it obtains exactly the samefrequency representation of the signal as it would get without cyclic prefix.

One slot could theoretically fit 7.5 symbols ( 500µs66.67µs = 7.5), therefore a slot contains

maximum 7 symbols and the remaining time of half of a symbol duration is usedas the cyclic prefixes for all 7 symbols, according to Table 4.1. In large cells, withhigher delay spread of the radio channel, the cyclic prefix must be extended andonly 6 symbols may be placed in a slot.

63


Figure 4.2: LTE FDD time domain structure.

Figure 4.3: Cyclic prefix concept.

4.2.2 TDD

In case of TDD, some of the subframes, in 10 ms long frame, are reserved for downlinktransmission, some subframes are reserved for uplink transmission and one or twosubframes have special structure, because they are used as switch points betweendownlink and uplink. Seven uplink-downlink configurations are supported, see Table4.2.

All subframes, which are not special subframes, are defined as two slots of length 0.5ms in each subframe. The special subframes consist of the three fields, see Figure4.4:

Figure 4.4: LTE TDD frame structure for UL-DL configuration 2.

• Downlink Pilot Time Slot (DwPTS),

64

4.3 Frequency domain structure

Prefix type

Number

of symbols

in a slot

∆f Cyclic prefix length

Propagation

path

difference

Normal7 15 kHz

5.2 µs for first symbol1.4 km

prefix 4.7 µs for other symbols

Extended 6 15 kHz 16.7 µs 5.0 km

prefix 3 7.5 kHz 33.3 µs 10 km

Table 4.1: Cyclic prefix types.

UL-DL UL-DL switch Subframe number

configuration point periodicity 0 1 2 3 4 5 6 7 8 9

0 5 ms ↓ S ↑ ↑ ↑ ↓ S ↑ ↑ ↑1 5 ms ↓ S ↑ ↑ ↓ ↓ S ↑ ↑ ↓2 5 ms ↓ S ↑ ↓ ↓ ↓ S ↑ ↓ ↓3 10 ms ↓ S ↑ ↑ ↑ ↓ ↓ ↓ ↓ ↓4 10 ms ↓ S ↑ ↑ ↓ ↓ ↓ ↓ ↓ ↓5 10 ms ↓ S ↑ ↓ ↓ ↓ ↓ ↓ ↓ ↓6 5 ms ↓ S ↑ ↑ ↑ ↓ S ↑ ↑ ↓

Table 4.2: Uplink-downlink configuration for LTE TDD. ↓ denotes a subframereserved for downlink transmission. ↑ denotes a subframe reserved for uplink trans-mission. S denotes a special subframe.

• Guard Period (GP),

• and Uplink Pilot Time Slot (UpPTS).

DwPTS, GP and UpPTS have configurable individual lengths (see Table 4.3 andFigure 4.5) and a total length of 1 ms.

4.3 Frequency domain structure

LTE downlink transmission is based on the OFDMA with the subcarrier bandwidthof 15 kHz. The LTE downlink physical resource can thus be seen as a time-frequencygrid, which consists of Resource Elements (REs), as illustrated in Figure 4.6. TheRE corresponds to one symbol duration in the time domain and subcarrier width(15 kHz) in frequency domain.

Since the idea of OFDMA is to divide the available channel bandwidth into manynarrow subcarriers and to allocate to a user several simultaneous subcarriers, there-fore a concept of a Resource Block (RB) is created. The RB corresponds to 12consecutive subcarriers (12·15 kHz = 180 kHz) used during one slot (0.5 ms), there-fore the RB consists of 12·7 = 84 RE. To provide user with higher bit rate, a usermay get simultaneously several RBs on one E-UTRAN carrier.

The number of RBs for the different LTE channel bandwidths is listed in Table 4.4.

65


Normal CP in downlink Normal CP in downlink

Special

DwPTS

UpPTS

DwPTS

UpPTS

subframe Normal Extended Normal Extended

config. CP in CP in CP in CP in

uplink uplink downlink downlink

0 6592·Ts

2192·Ts 2560·Ts

7680·Ts

2192·Ts 2560·Ts1 19760·Ts 20480·Ts

2 21952·Ts 23040·Ts

3 24144·Ts 25600·Ts

4 26336·Ts 7680·Ts

4384·Ts 5120·Ts5 6592·Ts

4384·Ts 5120·Ts

20480·Ts

6 19760·Ts 23040·Ts

7 21952·Ts – – –

8 24144·Ts – – –

Table 4.3: Special subframe configuration.

Figure 4.5: Special subframe configuration.

66

4.4 Scheduling Block

Figure 4.6: LTE downlink physical resource.

For example for channel bandwidth 5 MHz there are 25 RBs, which can be allocatedto users. The remaining frequency band is unused and needed as band guard, seealso Figure 4.7.

Channel bandwidth

[MHz]1.4 3 5 10 15 20

Transmission bandwidth

configuration

[RB]

6 15 25 50 75 100

Table 4.4: Number of RBs for different channel bandwidths in FDD and TDD.

4.4 Scheduling Block

Data is allocated to the UEs in form of Scheduling Block (SB). One SB consists oftwo RBs in the same subframe.

In DL, one UE can be allocated integer multiples of one SB in the frequency domain.These SBs do not have to be adjacent to each other. In the time domain, thescheduling decision can be modified every Transmission Time Interval (TTI) of 1ms. The scheduling decision is done in the eNB. The scheduling algorithm hasto take into account the radio link quality situation of different users, the overallinterference situation, QoS requirements, service priorities, etc. Figure 4.8 shows anexample of downlink data allocation to different users.

4.5 Virtual Resource Block

Resource blocks are used to describe the mapping of certain physical channels toresource elements. Both physical and virtual resource blocks are defined by 3GPPTS 36.211 .

67


Figure 4.7: Definition of channel bandwidth and transmission bandwidth configu-ration for one E-UTRAN carrier.

Figure 4.8: An example of DL resource allocation.

68

4.6 System spectral efficiency

Physical Resource Block (PRB) is what we have been discussing so far, RB with thefollowing properties: 180 kHz over 0.5ms.

A Virtual Resource Block (VRB) is of the same size as a PRB. Two types of VRBsare defined:

• VRB of localised type,

• VRB of distributed type.

4.5.1 VRB of localized type

When using localized VRBs then there is a direct mapping of VRB to the PRBs:nPRB = nVRB. It means that a SB consisting of two VRBs corresponds to twoPRBs located at the same place in the frequency domain, see Figure 4.9. VRBs arenumbered from 0 to NDL

VRB − 1, where NDLRB = NDL

VRB.

4.5.2 VRB of distributed type

When using distributed VRBs then the first PRB that belongs to the SB is trans-mitted on different subcarriers than the second PRB belonging to the same SB, seeFigure 4.9.

The parameter Ngap is given by Table 4.5. For 6 ≤ NRBDL ≤ 49 , only one gap value

Ngap,1 is defined and Ngap = Ngap,1. For 50 ≤ NRBDL ≤ 110, two gap values Ngap,1

and Ngap,2 are defined. Whether Ngap = Ngap,1 or Ngap = Ngap,2 is signalled as partof the downlink scheduling assignment.

VRBs of distributed type are numbered from 0 to NDLVRB − 1, where

NDLVRB = NDL

VRB,gap1 = 2 ·min(Ngap, NDLRB −Ngap) for Ngap = Ngap,1 and

NDLVRB = NDL

VRB,gap2 = ⌊NDL

RB2Ngap

⌋ · 2Ngap for Ngap = Ngap,2.

For example, if NDLRB = 100 then NDL

VRB = 2 ·48 = 96 for Ngap = Ngap,1. The NDLVRB is

used in the interleaving process as presented in Figure 4.9. The interleaving decidesabout the PRB number used for the first slot. The PRB, which transmit the secondslot of the SB, is shifted by Ngap compared to the first slot.

NRBDL 6 7-8 9-10 11 12-19 20-26 27-44 45-49 50-63 64-79 80-110

RBG 1 1 1 2 2 2 3 3 3 4 4

Ngap,1 3 4 5 4 8 12 18 27 27 32 48

Ngap,2 - - - - - - - - 9 16 16

Table 4.5: RB gap values.


Table 4.6 compares air interface characteristics of GSM, UMTS, WiMAX and LTEsystems. System spectral efficiency shows how many bits per second the systemcan transmit for each Hz of channel band width allocated in a cell. UMTS high

69


Figure 4.9: Localized and distributed VRB. The picture illustrates Ngap,1 = 48for NRB

DL = 100.

70


system spectral efficiency is achieved thanks to high symbol rate of 3840 ksym/sused for wide channel band width. In LTE higher system spectral efficiency isachieved even though the symbol rate is low, this is because the channel band widthis narrow.

User bit rate depends not only on the system spectral efficiency, but also on thefrequency band width allocated for the user as well as Carrier (C) to Noise (N)and Interferer (I) conditions C/(N+I). Low C/(N+I) may unable usage of highmodulation techniques like 64QAM. User bit rate may also be increased thanks tomultiple antennas used for transmission and for reception, so called MIMO concept,which is discussed in further in the book.

71


System

Radio

access

technique

(Sub)ca

rrier

bandwidth

Modulatio

n(Sub)carrier

bitrate

Spectral

efficien

cy

Freq

uency

reuse

System

spectral

efficien

cy

Symbol

duratio

n

Symbol

rateTech

nique

Schem

e

kHz

µs

ksymb

sbit

symb

kbits

bit/

sHz

freqcell

bit/

sHz·cell

GSM

TDMA

200

3.7271

GMSK

1271

1.3613

0.45

UMTS

WCDMA

5000

0.33840

QPSK

27680

1.5411

1.54

WiM

AX

OFDMA

10.94

91.4

10QPSK

220

1.8311

1.83

WiM

AX

OFDMA

10.94

91.4

1064QAM

660

5.4811

5.48

LTE

OFDMA

15

66.7

14QPSK

228

1.8711

1.87

LTE

OFDMA

15

66.7

1464QAM

684

5.6011

5.60

Table

4.6:GSM,UMTS,W

iMAX

andLTE

comparison

.Thetable

presen

tsgross

bitrate,

spectral

efficien

cyan

dsystem

spectral

efficien

cy,which

inclu

denoton

lyuser

date

bit

ratebutalso

system

signallin

g.Thetable

does

notcon

sider

MIM

Owhich

canfurth

erincrease

spectral

efficien

cy.

72

5 LTE downlink physical chan-nels

In the OFDMA technique, which is used in the LTE DL, each RE contains onecomplex number. The complex numbers, which are sent duration the same symbol,are input the IFFT to build the time domain signal. The time domain signal is nextconverted to analogue and transmitted by an antenna.

The complex numbers compose different physical channels, in order to support thesystem with not only user data transmission (carried out on PDSCH), but also withall kinds of signalling necessary to support this transmission.

This chapter presents the process of the complex numbers generation, which composedifferent physical channels.

5.1 Cell search

The cell search in a process of finding an LTE. The cell search is based on the Pri-mary Synchronisation Signals (P-SS) and Secondary Synchronisation Signals (S-SS)as well as the SI transmitted on the PBCH and PDSCH.

The first step of cell search in LTE is based on specific P-SS and S-SS. LTE uses ahierarchical cell search scheme similar to WCDMA. Thus, the P-SS and the S-SS aredefined. The synchronization signals are transmitted twice per 10 ms on predefinedslots, see Figure 5.1 for FDD and Figure 5.2 for TDD.

Figure 5.1: Primary/secondary synchronization signal and PBCH structure forFDD (normal cyclic prefix).

73

5 LTE downlink physical channels

Figure 5.2: Primary/secondary synchronization signal and PBCH structure forTDD (normal cyclic prefix).

5.2 P-SS

The P-SS is a sequence of 62 symbols transmitted on the 62 central subcarriers. Thesequence is generated from a frequency-domain Zadoff-Chu1 sequence. The Zadoff-Chu sequence has an ideal periodic auto-correlation property (i.e. the periodic auto-correlation is zero for all time shifts other than zero). Thanks to this property andalso thanks to location of the P-SS on the central subcarriers an UE may synchronizeto the subcarrier structure (frequency domain synchronization).

There are three different Zadoff-Chu root sequences defined in the 3GPP standard(3GPP TS 36.211) using root indices 25, 29, 34, corresponding to cell parameterphysicalLayerId = {0, 1, 2}, see Figure 5.3.

Identifying the sequence transmitted in a cell the UE can detect physicalLayerIdparameter. Different physicalLayerId should be allocated to neighbouring cellslocated on the same site. The different Zadoff-Chu root sequences are not orthogonal,but exhibit low cross-correlation2.

The P-SS is transmitted without being scrambled.

Since the P-SS occurs twice per frame it does not uniquely determine the frametiming, but has an ambiguity of 5 ms.

1A Zadoff-Chu sequence is a complex-valued mathematical sequence which have the propertythat cyclicly shifted versions of the sequence comprising the signal do not cross-correlate with eachother when the signal is recovered at the receiver. A generated Zadoff-Chu sequence that has notbeen shifted is known as a ”root sequence”. Zadoff-Chu sequences are used in the 3GPP LTE airinterface in the definition of Primary Synchronization Signal (P-SS), random access preamble (senton PRACH), HARQ ACK/NACK responses (sent on PUCCH) and Sounding Reference Signals(SRS).

2Correlation is a dependence between two variables. Intuitively, correlation between two vari-ables means, that if we know the value of one of them, then we are able, at least in some cases, topredict the value of the other variable with better accuracy than without this information. Cross-correlation is a measure of similarity of two waveforms as a function of a time-lag applied to one ofthem. This is also known as a sliding dot product or inner-product.

74

5.3 S-SS

Figure 5.3: Zadoff-Chu sequence transmitted on 31 lower frequency band subcar-riers for physicalLayerId = 0, which corresponds to root index u = 25.

The mapping of P-SS as well as other physical channels and physical signals isillustrated in Figure 5.4

5.3 S-SS

The sequence d(n) used for the S-SS is an interleaved concatenation of two length-31binary sequences s0(n) and s1(n), hence the total length is 62. The two sequencess0(n) and s1(n) are defined as two different cyclic shifts of a source sequence s(n),see Table 5.1.

Table 5.1: S-SS sequence generation.

The sequence s(n) is used to generate, by its cyclic shift, two sequences s0 and s1.The Table 5.1 shows cyclic shifts of 1 and 4 respectively, which sent in subframe 0encode physicalLayerCellIdGroup = 60. The sequences s0(n) and s1(n) are next

75


Figure 5.4: Mapping of Physical Channels on DL for FDD mode. Time on hori-zontal axis and frequency on vertical axis.

76

5.4 RS

concatenated with interleaving building 62-long sequence. The 3GPP standard spec-ifies 168 different pairs of shifts, therefore one of 168 different 62-long concatenatedbinary sequences may be transmitted on the S-SS, which encode the parameterphysicalLayerCellIdGroup = {0, 1, ....167}.

The concatenated sequence is next scrambled with a scrambling sequence givenby the P-SS.and, similar to the P-SS, transmitted on 62 central subcarriers. Thecombination of two length-31 sequences defining the S-SS differs between subframe 0and subframe 5 and is used to resolve the ambiguity of 5 ms mentioned above.

Parameters physicalLayerId and physicalLayerCellIdGroup compose the physicallayer cell identity according the below formula:

CellID = 3 · physicalLayerCellIdGroup+ physicalLayerId (5.1)

The above formula makes available 504 different physical layer cell identities. BothP-SS and S-SS must be transmitted on the same antenna port. Placing P-SS and S-SS close to each other enables coherent detection of S-SS using the channel estimateobtained from P-SS. A drawback of this placement is that the duration betweenP-SS and S-SS depends on the length of the CP and its length must therefore beblindly estimated.

5.4 RS

Reference Signals (RS) are transmitted in both downlink and uplink. The downlinkreference signals consist of so-called reference symbols, which are known symbols in-serted within in the OFDM time/frequency grid. This section discusses the downlinkRS, which enable:

• Coherent demodulation of other symbols into bits in UE. Without these ref-erence symbols it would be very difficult for the UE to demodulate symbolsinto bits in so dense modulations like 16-QAM and 64-QAM where differentbetween different modulation constellations may be small. If an NodeB is uses2 or 4 antennas for transmission then different RS are transmitted by eachantenna.

• Channel quality measurements for scheduling. Because the downlink RS aresent in whole frequency band of the carrier therefore measurements done byUE and provided to the NodeB may be used by the NodeB to allocate theoptimal downlink subcarriers for downlink transmission.

• Measurements for mobility. RS are transmitted with constant output power,therefore measurements on the m are good signal strength measure of a celland are used in cell reselection and handover process.

Specific predefined resource elements carry the cell specific reference signal, whichconsists of so called reference symbols. The reference symbols are transmitted every6-th subcarrier across the whole band of the carrier. In case of normal cyclic prefix,the reference symbols are transmitted on symbols 0 and 4 in each slot (for one or twoantenna ports) and also on symbol 1 for four antenna ports in a cell, see Figure 5.5.In case of extended cyclic prefix the reference symbols are transmitted on symbols

77


Figure 5.5: Downlink reference signal structure in a cell supporting non-MBSFNtransmission with normal cyclic prefix and CellID = 0.

78

5.5 PBCH

0 and 3 in each slot (for one or two antenna ports) and also on symbol 1 for fourantenna ports in a cell.

In case of one or two transmit antennas, each antenna has 4 reference symbols ina RB. In case of four transmit antennas in a cell, antenna ports 0 and 1 have fourreference symbols in a RB, while antenna ports 2 and 3 have two reference symbolsin a RB.

The reference symbols, which are sent on a particular symbol every 6-th subcarrieracross the carrier frequency band, compose a pseudo random sequence of QPSKmodulation symbols. The sequence is generated with use of Gold codes3 and dif-ferent pseudo random sequence is used for different symbols within a frame, butare repeated every 10 ms frame. The pseudo random sequences are different foreach physical layer CellID. Not only the random sequence, but also the frequencydomain location of the reference symbols depends on the CellID. The cell-specificfrequency shift of the reference symbols is given by:

νshift = Cell ID mod 6 (5.2)

Figure 5.6 illustrates the above formula.

Figure 5.6: Cell specific RS frequency shift.

Downlink RS are transmitted in all downlink subframes in a cell supporting non-MBSFN transmission. In case the subframe is used for transmission with MBSFN,only the first two OFDM symbols in a subframe can be used for transmission of cell-specific reference symbols. Downlink reference signals are defined for ∆f = 15 kHzonly.

5.5 PBCH

As additional help during cell search a set of parameters, called System Information(SI), is broadcast to all UEs in the whole cell area by the logical channel BCCH.The SI is divided into two parts. The static part is called Master InformationBlock (MIB) and is carried out by transport channels BCH. The dynamic partcontains different System Information Blocks (SIBs) and is carried out by DL-SCHas presented in Figure 5.7.

3A Gold code, also known as Gold sequence, is a type of binary sequence, used in telecommunica-tion (CDMA, LTE) and satellite navigation (GPS). Gold codes are named after Robert Gold. Goldcodes have bounded small cross-correlations within a set, which is useful when multiple devices arebroadcasting in the same range.

79


Figure 5.7: System information.

5.5.1 MIB

The MIB contains a limited number of the most essential and most frequently trans-mitted parameters that are needed to acquire other information from the cell, andis transmitted on PBCH. The MIB contains 24 bits of information plus 16 bits ofCyclic Redundancy Check (CRC) and transmits the following parameters:

• DL carrier bandwidth.

• PHICH configuration.

• System frame number.

The MIB uses a fixed schedule with a periodicity of 40 ms and repetitions madewithin 40 ms. The first transmission of the MIB is scheduled in subframe number0 of radio frames for which the SFN mod 4 = 0, and repetitions are scheduled insubframe number 0 of all other radio frames.

The PBCH is mapped onto the first four OFDM symbols of the second slot in thefirst subframe of every frame. In the frequency domain PBCH uses the 72 centresubcarriers, which corresponds to six resource blocks. Over one radio frame thiscorresponds to 4 symbols · 72 subcarriers = 288RE.

• In case of normal cyclic prefix, 48 REs (8 reference symbols per RB and 6RBs) are occupied by RS and thus 288 − 48 = 240 REs are used for PBCHper frame. This corresponds to 480 coded bits per frame, since QPSK is used.

• In case of extended cyclic prefix, 72 resource elements (12 reference symbols perresource block and 6 resource block) are occupied by RS and thus 288− 72 =216 resource elements are used for PBCH per frame. This corresponds to 432coded bits per frame, since QPSK is used.

80

5.6 PCFICH

The BCH transport block is encoded with a convolutional encoder. The BCH TTIis 40 ms and thus, in case of normal cyclic prefix, a BCH transport block of 4 ·480 =1920 bits is delivered to L1 every 40 ms. In case of extended cyclic the block sizeis of 4 · 432 = 1728 bits. The block of bits is scrambled with a cell-specific sequenceprior to modulation.

5.5.2 SIB

The remaining parameters are divided thematically into blocks, so called SIBs:

SIB1 contains information on e.g. access related information and schedulinginformation on how the other SIBs are scheduled.

SIB2 contains radio resource configuration information that is common for allUEs.

SIB3 transmits cell reselection parameters.

SIB4 contains info for intra frequency LTE neighbouring cell relevant for cellreselection.

SIB5 contains info for inter frequency LTE neighbouring cell relevant for cellreselection.

SIB6 contains info for UTRAN neighbouring cells relevant for cell reselection.

SIB7 contains info for GERAN neighbouring cells relevant for cell reselection.

SIB8 contains info for CDMA2000 neighbouring cells relevant for cell reselec-tion.

SIB9 contains home eNB name.

SIB10 contains an Earthquake and Tsunami Warning System (ETWS) primarynotification.

SIB11 contains and ETWS secondary notifications.

SIB12 contains a CMAS notification.

SIB13 contains the information required to acquire the MBMS control informa-tion associated with one or more MBSFN areas.

Each SIB is transmitted periodically. SIB1 uses a fixed schedule with a periodicityof 80 ms. SIBs other than SIB1 are carried in System Information (SI) messages.Mapping of SIBs to SI messages is flexibly configurable by schedulingInfoList in-cluded in SIB1. SIBs are transmitted on DL-SCH, which in turn is transmitted bythe physical channel PDSCH. The scheduling of the SIB is indicated by sending asingle System Information RNTI (SI-RNTI) on PDCCH.

Parameters transmitted in SIBs are listed in Appendix A on page 157.

5.6 PCFICH

The Physical Control Format Indicator Channel (PCFICH) carries information aboutthe number of OFDM symbols used for transmission of PDCCHs in a subframe. The

81


set of OFDM symbols possible to use for PDCCH in a subframe is given in Table5.2.

Subframe NDLRB > 10 NDL

RB ≤ 10

Subframe 1 and 6 in TDD 1, 2 2

MBSFN subframes on a carrier supporting both PMCHand PDSCH for 1 or 2 cell specific antenna ports

1, 2 2

MBSFN subframes on a carrier supporting both PMCHand PDSCH for 4 cell specific antenna ports

2 2

MBSFN subframes on a carrier not supporting PDSCH 0 0

All other cases 1, 2, 3 2, 3, 4

Table 5.2: Number of OFDM symbols used for PDCCH. The NDLRB is the downlink

bandwidth configuration, expressed in number of RB, see Table 4.4.

Reception of the PCFICH is essential to correct operation of the system. If thePCFICH is incorrectly decoded the terminal will neither know where to find thecontrol channels nor where the data region starts, and will therefore lose any DL-SCHdata transmission intended for the terminal as well as uplink scheduling grants

Two bits of information are coded into a 32-bit long sequence using a rate-1/16simplex code. The coded bits are scrambled with a cell-specific sequence, modulatedwith QPSK modulation and mapped to 16 resource elements grouped into 4 groupsof 4 elements each. The four groups are well-separated in frequency to obtain gooddiversity. Furthermore, to avoid inter-cell PCFICH collisions, the location of thefour groups in the frequency domain depends on the CellID.

The PCFICH is transmitted on the same set of antenna ports as the PBCH.

5.7 PDCCH

5.7.1 PDCCH usage

The Physical Downlink Control Channel (PDCCH) carries scheduling assignmentsand other control information:

• Downlink scheduling assignments indicating downlink transmission of PDSCH.

• Uplink scheduling grants informing the UE about grants of PUSCH. The up-link scheduling grants include:

◦ PUSCH resource indication,

◦ Transport format (coding and modulation to apply by the UE),

◦ HARQ related information.

• Power control commands of groups of terminals, which complements the powercontrol commands included in scheduling decisions.

82

5.7 PDCCH

5.7.2 PDCCH mapping

Multiple PDCCHs can be transmitted in a subframe. PDCCHs are mapped on thefirst (up to four) OFDM symbols within a subframe, see Figure 5.4. The actualnumber of symbols used for the PDCCHs may vary per subframe and is indicatedby PCFICH, see Table 5.2. Thus, each subframe can be said to be divided into acontrol region (including PCFICH, PHICH and PDCCH), followed by a data region(PDSCH). This maximises the spectral efficiency as the control signalling overheadcan be adjusted to match the instantaneous traffic situation.

Location of the PDCCH at the beginning of the subframe allows the terminal to de-code the downlink scheduling assignment prior to the downlink transmission. Thedownlink transmission, takes place on the PDSCH, which is mapped on upper sym-bols numbers in the subframe. This minimises the delay in the DL-SCH decodingand thus the overall downlink transmission delay. Mobile terminals that are notscheduled may turn off their receiver circuitry for a large part of the subframe, withreduces terminal power consumption.

5.7.3 PDCCH format

A PDCCH carries messages listed in section 5.7.2. Because multiple mobile termi-nals can be scheduled simultaneously, on both downlink and uplink, there must bea possibility to transmit multiple scheduling messages within each subframe. Thedifferent scheduling messages have different payload sizes. For example, supportingspatial multiplexing with non-contiguous allocation of resource blocks in the fre-quency domain require a larger scheduling message than an uplink grant supportingfrequency contiguous allocations only.

Note, that PDCCHs, which are sent to different terminals located in different radioconditions, may require different codec rate. Matching of the codec rate to differentradio conditions is supported and carried out by the Link Adaptation (LA) algo-rithm. Thus, the size of the PDCCH is variable and the PDCCH is transmitted onan aggregation of 1, 2, 4 or 8 consecutive Control Channel Elements (CCEs), wherea CCE corresponds to 9 Resource Element Groups (REGs) and each REG consistsof 4 RE, see Figure 5.8 and Table 5.3 (TS 36.211).

PDCCH Number of Number of Number of

format CCEs REG PDCCH bits

0 1 9 72

1 2 18 144

2 4 36 288

3 8 72 576

Table 5.3: Supported PDCCH formats.

5.7.4 PDCCH processing

The PDCCH processing consists of the following steps, which are also illustrated inFigure 5.9:

83


Figure 5.8: Control Channel Element (CCE).

Figure 5.9: Physical layer PDCCH processing.

84

5.7 PDCCH

• CRC attachment.

An CRC is attached to each PDCCH payload, where the MAC ID (RadioNetwork Temporary Identity (RNTI)) is included in the CRC calculation.Upon reception of a PDCCH, the terminal checks the CRC using its ownRNTI. If the CRC checks, the message is declared to be correctly receivedand intended for the terminal. Thus, the identity of the terminal, which issupposed to receive the PDCCH message, is implicitly encoded in the CRCand not explicitly transmitted.

• Channel coding and rate matching.

PDCCHs, which are sent to different terminals located in different radio condi-tions, may require different codec rate. Matching of the codec rate to differentradio conditions is supported and carried out by the Link Adaptation (LA)algorithm. The number of bits after coding and rate matching depends on thePDCCH format and is presented in Table 5.3.

• Multiplexing of CCEs.

The bits of coded PDCCHs are multiplexed in such a way, that bits of the firstPDCCH are put first and they are followed by bits of the second PDCCH andso on.

• Scrambling.

The block of multiplexed bits is scrambled by the cell specific scrabbling se-quence.

• Modulation.

The block of scrambled bits is modulated with QPSK modulation resulting ina block of complex-valued modulation symbols.

• Layer mapping and precoding.

The block of modulation symbols is mapped to layers to support the followingTX schemes:

◦ Transmission on a single antenna port.

◦ Transmit diversity with 2 or 4 layers. In transmit diversity there is alwaysone codeword and the number of layers is equal to the number of antennaports. For details on precoding for transmit diversity see Section 5.8.9.

The PDCCHs are transmitted on the same set of antenna ports as thePBCH.

5.7.5 PDCCH blind decoding

Each PDCCH may be of different format, see Table 5.3, and the number of CCEsbuilding the PDCCH is a-priori unknown to the UE. Therefore, the UE needs toblindly detect the format of the PDCCH. Because the PDCCH must start at CCE,which is a multiple of its size, therefore the number of blind decoding is reduced. Forexample, a PDCCH of size 4 CCEs can only start at CCE 0, 4, 8, etc. If the controlregion consists of only 8 CCEs the number of PDCCH candidates for blind decoding

85


is 15, see Figure 5.10. The UE tries to apply the MAC ID to each one PDCCHcandidates. First the UE assume that the PDCCH consists of 1 CCE, thereafter 2,4 and 8 CCEs. The UE knows that the PDCCH is intended for it if the CRC isOK.

If the number of CCEs is three times bigger then the number of channel PDCCHcandidates triples as well. Figure 5.11 shows an example of mapping of PDCCHsinto the Control Channel Element (CCE), when the control region consists of 24CCEs.

In order to reduce the number of decoding attempts the common search space andUE specific search spaces are also defined by the 3GPP:

• Common search space is used to send PDCCHs for all users or a group of users(e.g. indications about paging). All UEs monitor the common search space onPDCCH.

• The UE specific search space contains PDCCHs intended for one UE only (e.g.scheduling grants for transmitting UL data.) The UE uses its RNTI to findits specific search space.

5.8 PDSCH

The Physical Downlink Shared Channel (PDSCH) processing consists of two parts:

1. DL-SCH processing.

Figure 5.12 shows the processing structure for each transport block for the DL-SCH, PCH and MCH transport channels as described in TS 36.212. Data andcontrol streams from/to MAC layer are encoded/decoded to offer transportand control services over the radio transmission link. Channel coding schemeis a combination of: error detection, error correcting, rate matching, interleav-ing and transport channel or control information mapping onto/splitting fromphysical channels.

• CRC attachment,

• Code block segmentation,

• Channel coding,

• Rate matching,

• Code block concatenation.

2. Physical layer PDSCH processing.

Physical layer PDSCH processing is described in 3GPP 36.211 clause 6.3. Theprocessing consists of the following steps, which are also presented in Figure5.13:

• Scrambling.

Scrambling of coded bits in each of the code words to be transmitted ona physical channel.

86

5.8 PDSCH

Figure 5.10: PDCH blind decoding example.

Figure 5.11: PDCH blind decoding.

87


Figure 5.12: Transport channel processing for DL-SCH, PCH and MCH.

• Modulation mapper.

Mapping of scrambled bits to generate complex-valued modulation sym-bols.

• Layer mapper.

Mapping of the complex-valued modulation symbols onto one or severaltransmission layers. Layer mapper together with precoding are enablesfor MIMO.

• Precoding.

Precoding of the complex-valued modulation symbols on each layer fortransmission on the antenna ports.

• Resource element mapper on antenna ports.

Mapping of complex-valued modulation symbols for each antenna port toresource elements.

• OFDM signal generation.

Generation of complex-valued time-domain OFDM signal for each an-tenna port.

88

5.8 PDSCH

Figure 5.13: Physical layer PDSCH processing.

89


5.8.1 CRC attachment

Error detection is provided on transport blocks through a Cyclic Redundancy Check(CRC). CRC is used to detect if there are any uncorrected errors left after errorcorrection. The entire transport block a0, a1, ..., aA−1, where A is the size of theinput sequence, is used to calculate 24 parity bits of the CRC, which is attached tothe transport block bits a0, a1, ..., aA−1 as presented in Figure 5.14.

Original data10010111010011011...

Radio frequency transmission path

Transmitter

Receiver

Checksum 24 bits11001110110101...

Original data10010111010011011...

Received checksum11001110110101...

Received data10010101010011011...0

CRC generator

Regenerated checksum00001110011101...

CRC generator

If checksums do not matchthere is an error

Figure 5.14: CRC concept.

5.8.2 Code block segmentation

The input bit sequence to the code block segmentation (see Figure 5.12)is denotedby b0, b1, ..., bB−1, where B > 0. If B is larger than the maximum code block sizeZ, segmentation of the input bit sequence is performed and an additional CRCsequence of L = 24 bits is attached to each code block. The number of code blocksafter segmentation is denoted by C and the code blocks are numbered accordinglyr = 0, ..., C − 1.

The maximum code block size Z = 6144 bits.

5.8.3 Channel coding

The correction of bit errors, which may happen during air interface propagation, iscarried out by channel coding. Each code block is coded separately. The channelcoding consists of encoding on the transmitting side and decoding on the receivingside. The encoding carried out by adding redundant bits (coding bits) to the user

90

5.8 PDSCH

date bits on the transmitting side. The receiver performs decoding of the signal byremovals of the additional encoding bits and correcting possible bit errors.

The following channel coding schemes can be applied to TrCHs:

• Convolutional coding with rate 1/3, see Figure 5.15.

• Turbo coding. The scheme of turbo encoder is a Parallel ConcatenatedConvolutional Code (PCCC) with two 8-state constituent encoders and oneturbo code internal interleaver. The coding rate of turbo encoder is 1/3. Thestructure of turbo encoder is illustrated in Figure 5.16.

Usage of coding scheme and coding rate for the different types of TrCH is shown inTable 5.4.

TrCh Coding scheme Coding rate

UL-SCH

Turbo coding 1/3DL-SCH

PCH

MCH

BCH

Tail biting

convolutional

coding

1/3

Table 5.4: Usage of channel coding scheme and coding rate for control information.

D D DD D D

Figure 5.15: Rate 1/3 tail biting convolutional encoder.

Due to reflections from different objects, like for example buildings, the radio wavespropagate over several paths before they reach the receiver. The multipath propaga-tion results in constructive or destructive interference of radio waves, which propa-gate over different paths. The destructive interference causes signal attenuation. Thesignal attenuation leads to bursty errors (consecutive erroneous bits) that appearrepeatedly when receiver is moving. The decoder fails to recover bursty errors, butit successfully recovers single errors spread over the whole coding block. Thereforeturbo coding has an internal Quadrature Permutation Polynomial (QPP) interleaver,as shown in Figure 5.16, which spreads bursty errors over the whole coding blockand hence making the decoding more effective. The interleaver concept is presentedin Figure 5.17.

5.8.4 Rate matching

Rate matching algorithm repeats or punctures the bits of a mother codeword togenerate a requested number of bits according to a desired code rate that may

91


Turbo codeinternal

interleaver

D D D

1st constituent encoder

D D D

2nd constituent encoder

Figure 5.16: Structure of rate 1/3 turbo encoder (dotted lines apply for trellistermination only). The initial value of the shift registers of the 8-state constituentencoders is all zeros when starting to encode the input bits.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 ... 39

0 13 6 19 12 25 18 31 24 37 30 3 36 9 2 15 8 21 14 27 20 33 26 39 ... 7

Interleaver

Radio frequency transmission path

0 13 6 19 12 25 18 31 24 37 30 3 36 9 2 15 8 21 14 27 20 33 26 39 ... 7

Deinterleaver

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 ... 39

Time

Amplitude

12 25 18

12 18 25

Consecutiveerrors

To decoderDistributted errors

Transmitter

Receiver

Figure 5.17: Interleaver.

92

5.8 PDSCH

be different from the mother code rate of the turbo coder. The rate matchingalgorithm also facilitates enhanced HARQ operation by minimising repetition ofcoded bits (when possible) for subsequent retransmissions of a packet in order toincrease coding gains via Incremental Redundancy (IR).

The rate matching for turbo coded transport channel is presented in Figure 5.18. Foran input block size of K bits, the output of a turbo encoder consists of three length-K streams, corresponding to the systematic bit d(0) and two parity bit streams d(1)

and d(2), referred to as P1 and P2 respectively. In the Circular Buffer Rate Matching(CBRM) method for rate-1/3 turbo codes, which is used in LTE, each of the threeoutput streams of the turbo coder is rearranged with its own sub-block interleaver.Then, a single output buffer is formed by placing the rearranged systematic bits inthe beginning followed by bit-by-bit interlacing of the two rearranged parity streams.Interlacing allows equal levels of protection for each constituent code.

Figure 5.18: Operations of circular buffer rate matching for turbo code.

For a desired code rate, the number of coded bitsNdata to be selected for transmissionis passed to the rate matching algorithm. The bit selection step of the CBRM simplyreads out the first Ndata bits from the start of the buffer. In general, the bits to beselected for transmission can be read out starting from any point in the buffer. Ifthe end of the buffer is reached, then the reading continues by wrapping around tothe beginning of the buffer (hence the term circular buffer). Thus, puncturing andrepetition is achieved using a unified method.

IR based HARQ operation is a key performance enabler in LTE. Thus, an LTE RMalgorithm is expected to provide different subsets, denoted by Redundancy Version(RV), of the codeword for different transmissions of a packet (i.e., minimise repetition

93


of coded bits when possible). In CBRM, different RVs can be specified by simplydefining different starting points (to start reading out) in the CB. For the firsttransmission (RV = 0), it is conventionally assumed the bits are read out from thebeginning of the circular buffer, which means that all systematic bits are alwaysselected and puncturing, if needed, is applied to parity bits only.

5.8.5 Code block concatenation

If the transport block was segmented into code blocks, see section 5.8.2, then thecode blocks are concatenated. The number of code blocks is denoted by C and thecode blocks are numbered accordingly r = 0, ..., C − 1. The bits input to the codeblock concatenation are denoted by er0, er1, ..., er(Er−1) where Er is the number ofrate matched bits for the r-th code block, compare with Figure 5.12.

5.8.6 Scrambling

Each codeword q = 0, 1, the block of bits b(q)(0), b(q)(1), ..., b(q)(M(q)bit − 1), where

M(q)bit is the number of bits in code word transmitted on the physical channel in one

subframe, is scrambled prior to modulation, resulting in a block of scrambled bits

b̃(q)(0), b̃(q)(1), ..., b̃(q)(M(q)bit − 1) according to:

b̃(q)(i) =(b(q)(i) + c(q)(i)

)mod 2 (5.3)

The scrambling sequence c(q)(i) is different for each code word, CellID as well asRNTI associated with the PDSCH transmission. Up to two code words can betransmitted in one subframe.

5.8.7 Modulation mapper

For each codeword, the block of scrambled bits b̃(q)(0), b̃(q)(1), ..., b̃(q)(M(q)bit − 1) is

modulated using one of the three modulation schemes QPSK, 16QAM or 64QAM,presented in section 1.6, resulting in a block of complex-valued modulation symbols

d(q)(0), d(q)(1), ..., b(q)(M(q)symb − 1).

5.8.8 Layer mapper

The complex-valued modulation symbols, for each of the codewords to be trans-mitted, are mapped onto one or several layers. A layer is an isolated (from otherlayers) stream of modulation symbols that will be sent to the UE. Up to four layersmay be transmitted to the UE parallely increasing the downlink throughput. Theactual number of layers used for the transmission depends on the downlink radioconditions and is decided by the eNB on the bases of the UE report, mainly RankIndicator (RI), see section 7.5.

Each layer has the same number of symbols, but modulation and coding may differbetween the codewords.

94

5.8 PDSCH

Single antenna port

For transmission on a single antenna port, a single layer is used, υ = 1, and themapping is defined by:

x(0)(i) = d(0)(i) (5.4)

with M layersymb = M

(0)symb.

Spatial multiplexing

For spatial multiplexing, the layer mapping is done according to Table 5.5, which isalso illustrated in Figure 5.19. The number of layers υ = 1 is less than or equal tothe number of antenna ports P used for transmission of the physical channel. Thecase of a single code word mapped to two layers is only applicable when the numberof antenna ports is 4.

Figure 5.19: Codeword-to-layer mapping for spatial multiplexing and transmitdiversity. The picture also presents the precoding for transmit diversity. The sizeof the codeword(s) correspond to the maximum throughput possible to achieve forparticular layer mapping. It can be observed that in spatial multiplexing maximumthroughput increases with the the number of layers. In transmit diversity, regardlessof the number of antennas, the maximum throughput is not increased.

Trasmit diversity

For transmit diversity, the layer mapping is done according to Table 5.6, which isalso illustrated in Figure 5.19. There is only one codeword and the number of layersυ = 1 is equal to the number of antenna ports P used for transmission of the physicalchannel.

95


Number Number Codeword-to-layer mapping

of layers of codewords i = 0, 1, ...,M layersymb − 1

1 1 x(0)(i) = d(0)(i) M layersymb = M

(0)symb

2 2x(0)(i) = d(0)(i)

x(1)(i) = d(1)(i)M layer

symb = M(0)symb = M

(1)symb

2 1x(0)(i) = d(0)(2i)

x(1)(i) = d(0)(2i+ 1)M layer

symb = M(0)symb/2

3 2

x(0)(i) = d(0)(i)

x(1)(i) = d(1)(2i)

x(2)(i) = d(1)(2i+ 1)

M layersymb = M

(0)symb = M

(1)symb/2

4 2

x(0)(i) = d(0)(2i)

x(1)(i) = d(0)(2i+ 1)

x(2)(i) = d(1)(2i)

x(3)(i) = d(1)(2i+ 1)

M layersymb = M

(0)symb/2 = M

(1)symb/2

Table 5.5: Codeword-to-layer mapping for spatial multiplexing.

Number Number Codeword-to-layer mapping

of layers of codewords i = 0, 1, ...,M layersymb − 1

2 1x(0)(i) = d(0)(2i)

x(1)(i) = d(0)(2i+ 1)M layer

symb = M(0)symb/2

4 1

x(0)(i) = d(0)(4i)

x(1)(i) = d(0)(4i+ 1)

x(2)(i) = d(0)(4i+ 2)

x(3)(i) = d(0)(4i+ 3)

M layersymb = M

(0)symb/4

∗

Table 5.6: Codeword-to-layer mapping for transmit diversity.∗In case whenM

(0)symb mod 4 ̸= 0 then two null symbols are appended to d(0)(M

(0)symb−

1).

96

5.8 PDSCH

5.8.9 Precoding

The precoder maps layers onto resources on each of the antenna ports. There areseveral variants of precoding:

• Precoding for transmission on a single antenna port,

• Precoding for spatial multiplexing,

◦ Precoding without Cyclic Delay Diversity (CDD),

◦ Precoding for large delay CDD,

• Precoding for diversity.

Single antenna port

Precoding for transmission on a single antenna port is defined by:

y(p)(i) = x(0)(i) (5.5)

where p ∈ {0, 4, 5, 7, 8} is the number of the single antenna port used for transmission

of the physical channel and i = 0, 1,M apsymb − 1, M ap

symb = M layersymb.

Spatial multiplexing

Precoding for spatial multiplexing using antenna ports with cell-specific referencesignals is only used in combination with layer mapping for spatial multiplexing.Spatial multiplexing supports two or four antenna ports and the set of antennaports used is p ∈ {0, 1} or p ∈ {0, 1, 2, 3}, respectively.

• Precoding without CDD is defined by:

y(0)(i)...

y(P−1)(i)

= W (i)

x(0)(i)...

x(υ−1)(i)

(5.6)

where the precoding matrix W (i) is of size P × υ and i = 0, 1, ...,M apsymb − 1,

M apsymb = M layer

symb.

For spatial multiplexing, the values of W (i) are selected among the precoderelements in the codebook configured in the eNB and the UE. The eNB canfurther confine the precoder selection in the UE to a subset of the elementsin the codebook using codebook subset restrictions. For 2 antenna ports,a codebook index from Table 5.7 must be selected. Different code book isspecified for 4 antenna transmission.

Figure 5.20 presents the precoding matrix W (i) selection for a relatively sim-ple case of spatial multiplexing with one layer and two antenna ports. Thistechnique is also called beamforming. The possible precoding matrixes, whichmay be applied in this case, are presented in Table 5.7 in the column υ = 1.

97


Codebook Number of layers υ

index 1 2

0 1√2

[1

1

]1√2

[1 0

0 1

]

1 1√2

[1

−1

]12

[1 1

1 −1

]

2 1√2

[1

j

]12

[1 1

j −j

]

3 1√2

[1

−j

]–

Table 5.7: Codebook for transmission on antenna ports {0, 1}.

Figure 5.20: Spatial multiplexing with one layer and two antenna ports.

98

5.8 PDSCH

Let us assume that currently W = 1√2

[1

1

]is used. Signals transmitted from

antennas can be calculated as follows:

[y(0)

y(1)

]=

1√2

[1

1

]x(0) (5.7)

y(0) = 1√2(1 · x(0)) = 1√

2x(0)

y(1) = 1√2(1 · x(0)) = 1√

2x(0)

(5.8)

It can be seen from the above formulas that, for W = 1√2

[1

1

], both antennas

transmit exactly the same signal. It means, that the transmitted signals havethe same phase. This is advantageous for the UE located in front of thetransmitted antennas, where it has equal distances to both antennas. Signalstransmitted from both antennas will change their phases during propagation,but, because they cover the same distance, they will reach the UE with thesame phase leading to constructive interference and producing a gain in theUE antenna.

The UE may change its location in the cell and move to an area, where it iscloser to the antenna TX0 (denoted by red colour in the figure) than to theantenna TX1 (denoted by blue colour in the figure). If the difference in thepaths is equal λ/4, then the blue wave reaches the UE later, with a phasedelay of 90 degrees, compared to the red wave. To compensate the phase shift,the blue antenna should start its transmission earlier, which is achieved byshifting its phase by −90 degrees. The phase shift takes place in the precoderby multiplying the transmuted symbol x(0) by −j. Multiplication by −j, whichin the exponential notation is equal to e−

π2j , results in −90 degree (−π

2 ) phaseshift. (For exponential notation of complex numbers see section 1.3.5). The

required phase shift is achieved by precoding matrix W = 1√2

[1

−j

], which

does not apply any phase shift (coefficient 1) to antenna port 0 and applies aphase shift of −90 degrees (coefficient −j) to the antenna port 1.

Figure 7.13 shows that, when the user moves further to the side of the cell,the difference between paths increases and may reach λ/2. λ/2 is a distancebetween TX antennas, if polarisation diversity is not used, see Figure 5.20.If the phase of the signals is not modified by the precoded, the two signalsreach UE with opposite phase leading to destructive interference and signalcancelation. Because the blue signal has half of the wave length longer pathto cover, it reaches the UE with a phase shift of 180 degrees compared tothe red signal. 180 degree (π) phase shift is realised by multiplying a signalby ejπ = −1. Therefore, the best precoding matrix for this UE location

is W = 1√2

[1

−1

], which does not apply any phase shift (coefficient 1) to

99


antenna port 0 and a phase shift of 180 degrees (coefficient −1) to the antennaport 1.

It can be seen from Table 5.7, that, for spatial multiplexing with one layer,no phase shift is applied to the signal transmitted from antenna port 0 (in allmatrixes the coefficient corresponding to the antenna port 0 is equal 1). Thephase shift is applied to the signal transmitted from antenna port 1 and thepossible phase shifts are: 0 degree (coefficient 1), 180 degrees (coefficient −1),90 degrees (coefficient j) and −90 degrees (coefficient −j).

• Precoding with large delay CDD is defined by: y(0)(i)...

y(P−1)(i)

= W (i)D(i)U

x(0)(i)...

x(υ−1)(i)

(5.9)

where the precoding matrix W (i) is of size P × υ and i = 0, 1, ...,M apsymb − 1,

M apsymb = M layer

symb. The diagonal size-υ × υ matrix D(i) supports cyclic delaydiversity and is specified in TS 36.211 6.3.4.2.2. The size-υ × υ matrix U isalso specified in TS 36.211 6.3.4.2.2.

Transmit diversity

Precoding for transmit diversity is only used in combination with layer mapping fortransmit diversity described above. The precoding operation for transmit diversityis defined for two and four antenna ports.

For transmission on two antenna ports, p ∈ {0, 1}, the output

y(i) =[y(0)(i) y(1)(i)

]T, i = 0, 1,M ap

symb − 1 of the precoding operation is defined

by: y(0)(2i)

y(1)(2i)

y(0)(2i+ 1)

y(1)(2i+ 1)

=1√2

1 0 j 0

0 −1 0 j

0 1 0 j

1 0 −j 0

Re

(x(0)(i)

)Re

(x(1)(i)

)Im

(x(0)(i)

)Im

(x(1)(i)

) (5.10)

for i = 0, 1, ...,M apsymb − 1 with M ap

symb = 2M layersymb.

It can be seen from the equation 5.10 that in the transmit diversity two differentmodulation symbols x(0)(i) and x(1)(i), that come from different layers, are trans-mitted simultaneously by different antennas and are transmitted twice, which is alsoillustrated in Figure 5.19. First antenna port 0 transmits modulation symbol x0(i)and at the same time antenna port 1 transmits modulation symbol x1(i). Next an-tenna port 0 transmits modulation symbol x(1)(i) and at the same time antenna port1 transmits modulation x(0)(i), but with changed phase. This technique results insending each modulation symbol twice in different directions and therefore increasesprobability of successful reception.

For transmission on four antenna ports p ∈ {0, 1, 2, 3} the output y(i) is describedin TS 36.211 6.3.4.3 and not presented in this book.

100

5.9 PHICH

5.8.10 Resource element mapping

For each of the antenna ports used for transmission of the physical channel, the blockof complex-valued symbols y(p)(0), ..., y(p)(M ap

symb−1) is mapped in sequence starting

with y(p)(0) to resource elements (k, l) which meet all of the following criteria:

• they are in the physical resource blocks corresponding to the virtual resourceblocks assigned for transmission, and

• they are not used for transmission of PBCH, synchronisation signals, cell-specific reference signals, MBSFN reference signals or UE-specific referencesignals, and

• they are not in an OFDM symbol used for PDCCH.

The mapping to resource elements (k, l) on antenna port p not reserved for otherpurposes shall be in increasing order of first the index k over the assigned physicalresource blocks and then the index l, starting with the first slot in a subframe.

5.9 PHICH

The Physical Hybrid ARQ Indicator Channel (PHICH) is used for transmissionof hybrid-ARQ acknowledgements in response to UL-SCH transmission. There isone PHICH present for each terminal expecting an acknowledgement in the sub-frame.

Each PHICH carries one bit, which is repeated three times, modulated, spread witha spreading factor of four and mapped to three REGs. Multiple PHICHs form aPHICH group and the PHICHs within a PHICH group are code-multiplexed usingdifferent orthogonal sequences and share the same set of resource elements, seeFigure 5.21. There is in total eight 3GPP defined orthogonal sequences availablewhen using normal CP. Four orthogonal sequences are available in case of extendedCP. The use of use of code division multiplexing is motivated by power control ofthe PHICH, because with code division multiplexing the power difference betweensubcarriers is not as large as with pure frequency division multiplexing. The capacityof PHICH depends on the configured number of PHICH groups. Each PHICH groupis assigned a unique frequency resource.

Typically, the PHICH is transmitted in the first OFDM symbol only. However,in some propagation environments, this would unnecessarily restrict the PHICHcoverage. To alleviate this, it is possible to configure a PHICH duration of threeOFDM symbols10. In this case the control region is three OFDM symbols long inall subframes.

The PHICH configuration is part of the system information (MIB on the BCH);one bit indicates whether the duration is one or three OFDM symbols and two bitsindicate the amount of resources set aside for PHICHs.

101


Figure 5.21: PHICH.

5.10 PMCH

The Physical Multicast Channel carries DL transmission of the MCH transportchannel.

5.11 Downlink physical channels modulation sum-mary

Table 5.8 shows modulations used for different physical channels and physical signals,which were discussed in this chapter.

Physical channel

or physical signalModulation

P-SS Zadoff-Chu sequence

S-SS Interleaved concatenation of two length-31 binary se-quences

RS Gold sequence (pseudo random) of QPSK symbols

PBCH QPSK

PCFICH QPSK

PDCCH QPSK

PDSCH QPSK, 16-QAM, 64-QAM

PHICH BPSK

Table 5.8: DL physical channels modulation.

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6 LTE uplink physical channels

During the LTE development phase different alternatives for the optimum uplinktransmission scheme were investigated. While OFDMA is seen optimum to fulfil theLTE requirements in DL, OFDMA properties are less favourable for the UL. This ismainly due to worse Peak-to-Average Power Ratio (PAPR) properties of an OFDMAsignal, resulting in worse UL coverage. Thus, the LTE UL transmission scheme forFDD and TDD mode is based on Single Carrier Frequency Division Multiple Access(SC-FDMA) with cyclic prefix. SC-FDMA signals have better PAPR propertiescompared to an OFDMA signal, see Figure 6.1. This was one of the main reasonsfor selecting SC-FDMA as LTE UL access scheme. The PAPR characteristics areimportant for cost-effective design of UE power amplifiers. Still, SC-FDMA signalprocessing has some similarities with OFDMA signal processing, so parametrisationof downlink and uplink can be harmonised.

Figure 6.1: SC-FDMA versus OFDMA spectral power distribution.

There are different possibilities of SC-FDMA signal generation. Discrete FourierTransform spread-OFDM (DFT-s-OFDM) has been selected for LTE.

The principles of the DFT-s-OFDM are illustrated in Figure 6.2. A size-M DFT isfirst applied to a block of M modulation symbols (i.e. complex numbers). QPSK,16QAM or 64QAM may be used as uplink modulation schemes, the latter beingoptional for the UE. The DFT transforms the M modulation symbols into anotherM modulation symbols in the frequency domain. The result is mapped onto theM available UL subcarriers, that is inputs of the size-N IDFT. Unused inputs ofthe IDFT are set to zero. In UL, only localised transmission on consecutive Msubcarriers is allowed. An size-N IDFT, where N > M , is then performed as inOFDM (see Figure 1.20), followed by addition of the cyclic prefix and parallel toserial conversion.

M is the number of transmitted subcarriers and changes during UL transmission.For example, if the currently transmitted bandwidth by the UE is equal to 6 RBs

103


Figure 6.2: Block diagram of the UL DFT-s-OFDM transmitter.

then M = 6 · 12 = 72. N is the size of the IDFT build in the UE microprocessorand in LTE is equal to N = 211 = 2048, the same as in DL.

If the DFT size M would equal the IDFT size N , the cascaded DFT and IDFTblocks of Figure 6.2 would completely cancel out each other. However, if M issmaller than N and the remaining inputs to the IDFT are set to zero, the outputof the IDFT will be a signal with ’single-carrier’ properties, i.e. a signal with lowpower variations, and with a bandwidth that depends on M .

6.1 PUSCH

The UL SC-FDMA subcarrier spacing equals ∆f = 15 kHz and RBs, consisting of12 subcarriers in the frequency domain, are defined also for the UL. However, incontrast to the DL, no unused DC subcarrier is defined for the UL as this woulddestroy the ’single-carrier’ property of the UL transmission (single-carrier charac-teristics require the transmission of consecutive subcarriers).

Similar to the DL, the SC-FDMA used for the UL, also allows for a very high degreeof flexibility in terms of transmission bandwidth by allowing for, in essence, anynumber of UL subcarriers. However, from a DFT implementation point of view,the DFT size M should preferably be constrained to a power of 2 (M = 2n). Onthe other hand, such constraint is in direct conflict with a desired flexibility of ULbandwidth allocation to different terminals. From a flexibility point of view, allpossible values of M should rather be allowed. For LTE, a middle way has beenadopted where the DFT size is limited to products of the integers two, three andfive (M = 2α · 3β · 5γ , where α, β, γ = 0, 1, 2, ...). Thus, as an example, DFT of

104

6.1 PUSCH

sizes 84 is not allowed, because 84 = 2 · 2 · 3 · 7. Observe, that M = 84 = 12 · 7correspond to 7 RBs, therefore 7 RBs allocation is not allowed. As a consequence,the number of UL RBs allocation is also limited to products of the integers two,three and five.

Figure 6.3: UL resource allocation.

Also in terms of the more detailed time-domain structure the LTE UL is very similarto the DL. Each 1 ms UL subframe consists of two slots of length Tslot = 0.5ms,see Figure 6.4. Each slot consists of seven or six DFT-s-OFDM blocks including thecyclic prefix. Also similar to the downlink, two cyclic prefix lengths, a normal cyclicprefix (for seven DFT-s-OFDM blocks symbol) and an extended cyclic prefix (forsix DFT-s-OFDM blocks symbol) are defined for the UL.

Figure 6.4: UL subframe structure for normal cyclic prefix.

In Figure 6.3, UEs gets radio resources on the same subcarriers in the two slots.As an alternative, inter slot frequency hopping may be applied for the LTE uplink.In this case different frequencies are used for transmission in the two slots of asubframe as presented in Figure 6.5. There are two potential benefits with ULfrequency hopping if the hopping pattern are different in neighbouring cells.

• Frequency diversity.

• Interference averaging.

105


Figure 6.5: UL frequency hopping.

6.2 Uplink reference signals

There are two types of UL reference signals in LTE:

• Reference Signals (RS) for channel estimation to support coherent uplinktransmission.

• Sounding Reference Signal (SRS) to support UL frequency dependent schedul-ing.

6.2.1 RS

As illustrated in Figure 6.6, the uplink RSs used for channel estimation are trans-mitted within the fourth DFT-s-OFDM block of each uplink slot1 and with aninstantaneous bandwidth equal to the bandwidth of the data transmission.

Figure 6.6: UL RS.

The UL RS use cyclic extensions of Zadoff-Chu sequences at allocations of threeRBs (36 subcarriers) or more. The exceptions are the allocation of 1 or 2 RBs (12or 24 subcarriers), which instead use QPSK-based sequences. This is because thereare too few Zadoff-Chu sequences available at such short sequence lengths.

1This assumes the normal cyclic prefix, i.e. seven DFT-s-OFDM blocks per slot.

106

6.3 PUCCH

6.2.2 SRS

Channel dependent scheduling, in both the time and frequency domain, is a key LTEtechnology. The RS allow for UL channel estimation on the subcarriers, which arecurrently used by the UE’s PUSCH. The intention with the SRS is for the networkto estimate the channel quality of the uplink frequencies, which are currently notused by UE’s PUSCH transmission. The sounding reference signals can also be usedto estimate the timing of UE transmissions and to derive timing control commandsfor UL time alignment.

SRS are transmitted independently of the UE’s PUSCH transmission, i.e. a UE maytransmit the SRS also in subframes, where it does not have any data transmission.Furthermore, the bandwidth of SRS can be, and typically is, different from that ofthe UE’s PUSCH.

The SRSs are transmitted within the last DFT-s-OFDM block of a subframe asshown in Figure 6.7. The SRS resources are shared by a number of UEs by theirmultiplexing in the time, frequency and orthogonal codes domain:

• SRS in the time domain.

Different UEs may by configured to transmit SRS in different subframes byproviding the UE with SRS periodicity and SRS subframe offset. The period-icity of the SRS transmission is selected from the set {2, 5, 10, 20, 40, 80, 160,320} ms or subframes.

• SRS in the frequency domain.

UE may be configured to transmit SRS in the whole or a fraction of theUL carrier bandwidth. For example, if srs-BandwidthConfig = 2 in a cell with5 MHz UL bandwidth then some UEs in the cell may be configured to transmitSRS in the bandwidth of 24 RBs, some in the bandwidth 4 RBs and some inthe bandwidth of 4 RBs.

• SRS orthogonal codes.

Similar to the RS, the SRS is a Zadoff-Chu sequence. With cyclic shifts up to8 shift can be configured, which implies that up to 8 UEs can transmit SRSin the same time and in the same bandwidth but with different orthogonal(independent) sequences.

Example of the SRS allocation is illustrated in Figure 6.7.

6.3 PUCCH

PUCCH supports uplink L1/L2 control signalling, which carriers one (or more) ofthe following singling information:

• HARQ acknowledgements related to reception of DL-SCH transport. HARQacknowledgements are sent by PUCCH format 1A, 1B or PUSCH.

• Scheduling requests, used by the terminal to request UL-SCH resources in caseit does not have a valid scheduling grant. Scheduling request are transmittedon the PUCCH format 1.

107


Figure 6.7: UL SRS.

• Channel Quality Indicator (CQI) indicating the downlink channel quality per-ceived by the terminal. CQI is used by the network for DL modulation andcoding scheme selection. The CQI reports are transmitted periodically onPUCCH format 2 or aperiodically on PUSCH. UE reporting is discuss insection 7.5.

As illustrated in Figure 6.8, these resources are located at the edges of the totalavailable system bandwidth. Each such resource consists of 12 subcarriers (one re-source block) within each slot of an uplink subframe. To provide frequency diversity,these frequency resources are frequency hopping on the slot boundary, that is oneL1/L2 control resource consists of 12 subcarriers at the upper part of the spectrumwithin the first slot of a subframe and an equally sized resource at the lower part ofthe spectrum during the second slot of the subframe or vice versa, and it is referredto as a resource block pair.

If more resources are needed for the uplink L1/L2 control signalling, for example,in case of very large overall transmission bandwidth supporting a large number ofusers, additional resources blocks can be assigned next to the previously assignedresource blocks.

Figure 6.8: PUCCH resources.

108

6.3 PUCCH

6.3.1 PUCCH format 1A/1B

PUCCH format 1A and 1B are used for transmission of HARQ acknowledgements.

• Format 1A supports one bit acknowledgement to one code word.

• Format 1B supports two bits acknowledgement to two code words sent to theUE during one subframe, which is the case of spacial multiplexing.

One (format 1A) or two (format 1B) acknowledgement bits are modulated usingBPSK or QPSK, respectively, resulting in one complex number (modulation sym-bol).

A length-12 Constant Amplitude Zero AutoCorrelation (CAZAC) sequence is ap-plied to each symbol in order to spread the symbol over 12 symbols sent on differentsubcarriers of an RB. Different cyclic shift of the length-12 CAZAC sequence areapplied by different users, therefore 12 UEs feedbacks can be transmitted over thesame subcarriers in the same time. Then scrambling is applied to all the symbols,see Figure 6.9. Different scrambling codes are used in the two different slots withinone subframe.

The 12 complex numbers are further multiplied by an orthogonal cover sequence.Orthogonal cover sequences are applied to both the four information symbols in aslot as well as to the three reference signal symbols. Thus, with three referencesymbols per slot, up to three orthogonal cover sequences can be used. This impliesthree different UEs acknowledgements can be transmitted at the same cyclic shiftof the length-12 CAZAC sequence resulting in up to 3 · 12 = 36 UEs with PUCCHformat 1A/1B sharing one resource block pair.

The same PUCCH structure is used in the two slots of a subframe. To further ran-domise the inter-cell interference between PUCCH resource blocks, cyclic shift hop-ping (per OFDM symbol) and orthogonal cover hopping (per slot) are used.

Figure 6.9: PUCCH format 1.

HARQ acknowledgements are transmitted at a fixed time after the reception of aDL-SCH transport block (4 subframes in case of FDD). Furthermore, the PUCCHresource to use is derived from the index of the first control channel element in the

109


PDCCH used for scheduling the downlink transmission (or from RRC signalling incase of persistent scheduling).

6.3.2 PUCCH format 1

PUCCH format 1 is used for transmitting scheduling requests. The overall structureis similar to that used for HARQ acknowledgements. Each active terminal is assigneda dedicated resource for scheduling request through RRC signalling, providing thepossibility to request an uplink grant every x subframe.

If the UE do not want more scheduling, then it will not transmit anything on thededicated resources.

6.3.3 PUCCH format 2

PUCCH format 2 is used for CQI reports. The CQI reports are coded to 20 bits andscrambled. The scrambling sequence depends on the CellID, slot number and CellRNTI (C-RNTI). The scrambled bits are then modulated using QPSK, resulting in10 complex valued symbols, see Figure 6.10. Each of the QPSK symbols (assumingnormal cyclic prefix) is multiplied by a cyclically shifted length-12 CAZAC sequenceand transmitted in one DFT-s-OFDM symbol. As the same underlying principleof cyclically shifted CAZAC sequences is used for PUCCH format 2 as for format1A/1B, CQI from different terminals can be transmitted on the same time-frequencyresource by assigning different cyclic shifts. In theory, it is possible to use 12 differentcyclic shifts, hence twelve different UE’s CQI can be transmitted in the same resourceblock pair.

Figure 6.10: PUCCH format 2.

It is also possibility for one UE to send CQI reports together with ACK/NACK.In that case format 2A or 2B is used. However, it is also possible to mix different

110

6.4 PRACH

formats, i.e. different UEs transmit different feedback (e.g. CQI and ACK/NACK)in the same resource block. This is then signalled by higher layers.

6.4 PRACH

In the LTE, the UE uses the Random Access (RA) process to gain an access to acell for the following reasons:

• Initial access to the network from the RRC IDLE state.

• Regaining access to the network after a radio link failure.

• As part of the handover process to gain timing synchronisation with a newcell.

• Before uplink data transfers when the UE is in RRC CONNECTED, but notUL time synchronised with the cell. When UE is RRC CONNECTED andUL synchronised then it uses scheduling request on PUCCH to request for ULtransmission.

In both RRC IDLE and RRC CONNECTED the UE is time synchronise to the DLBCCH, however, due to the propagation (round trip) delay, there is a timing uncer-tainty in the uplink. Therefore, the RA process is used by the UE to obtain timesynchronisation. The PRACH shall reserve a sufficient time window to accommo-date various arrival times. During this time the UE transmits RA preamble. Fiveformats of RA preamble exist (0, 1, 2, 3 and 4) (TS 36.211), see Table 6.1, which isillustrated in Figure 6.11. Format 4 is used in TDD only.

Preamble format TCP TSEQ

0 3168 · Ts 24576 · Ts

1 21024 · Ts 24576 · Ts

2 6240 · Ts 2 · 24576 · Ts

3 21024 · Ts 2 · 24576 · Ts

4∗ 448 · Ts 4096 · Ts

Table 6.1: Random access preamble parameters.

Ts ≃ 32.55 ns, see equation 7.1.∗TDD mode and special subframe configurations with UpPTS lengths 4384 · Ts and5120 · Ts only.

The RA preamble has different subcarrier spacing than other UL channels. Durationof the RA preamble symbol is 0.8 ms, therefore RA subcarrier spacing is 1/800 ms= 1250 Hz. The RA preamble consists of 840 such subcarriers leading to the totaleffective bandwidth of 840 · 1250Hz = 1.05MHz. The bandwidth reserved for a RAopportunity is 1.08 MHz (6 RBs), so it is slightly bigger leaving small spectral guardbands on each side of the RA preamble. This is necessary since RA and regular ULdata are separated in frequency domain, but are not completely orthogonal.

The parameter prach-ConfigIndex specifies the preamble format and subframes wherewhere PRACH is allowed (TS 36.211). Location of the PRACH in the frequency do-

111


Figure 6.11: Preamble formats.

112

6.4 PRACH

main is defined by the parameter prach-FreqOffset, which indicated the RB allocatedfor the PRACH opportunity, which is illustrated in Figure 6.12.

Figure 6.12: Time-frequency structure of non-synchronised RA for FDD. Examplefor prach-ConfigIndex = 6 and prach-FreqOffset = 1.

113


114

7 Physical layer procedures

7.1 Timing advance

7.1.1 Uplink-downlink frame timing

From the eNodeB perspective, the uplink and downlink frames have defined timeshift equal to NTAoffsetTs, where NTAoffset = 0 for frame structure 1 used in FDDand NTAoffset = 614 for frame structure 2 used in TDD, as presented in the upperpart of Figure 7.2.

Ts is the sampling time, which is the time unit used in LTE and specified in 3GPP36.211 as follows:

Ts =1 s

15000

2048≃ 32.55 ns, (7.1)

where 1 s15000 is the symbol duration and 2048 is the FFT size. Thus, in case of

the frame structure 2 the uplink frame starts 614Ts ≃ 20.0µs earlier than downlinkframe.

7.1.2 Timing advance range

In order to keep the alignment of downlink and uplink frames at the eNB as specifiedby theNTAoffset, the UE must advance its uplink transmission compared to the signalreceived on downlink. The time advance compensates the radio waves propagationdelay from the eNB to the UE and back to the eNB. Therefore, from the UE perspec-tive, transmission of the uplink radio frame number shall start (NTA +NTAoffset)Ts

earlier than the start of the corresponding downlink radio frame at the UE, where0 ≤ NTA ≤ 20512. The maximum timing advance 20512Ts ≃ 667.7µs correspondsto the cell range of 100 km. Figure 7.1 and Figure 7.2 present the time advancecompensation for FDD and TDD respectively.

Initially NTA is received by the UE from the eNB in the timing advance commandduring random access and next is continuously adjusted by timing advance com-mands sent in the MAC control element.

7.1.3 Random access

Initial time alignment is performed by the random access process. Random accessresponse carries 11-bit timing advance command TA = 0, 1, 2, ..., 1282 and indicates

115


Figure 7.1: Uplink-downlink timing relation from UE perspective for FDD.

Figure 7.2: Uplink-downlink time relation from UE perspective for TDD.

116

7.1 Timing advance

NTA value (3GPP TS 36.213), which is presented in Figure 7.3:

NTA = 16TA, (7.2)

which means that the maximum timing advance value sent on the random accesschannel is 16 · 1282 ·Ts ≃ 66.77ms and corresponds to the distance of 100 km.

Figure 7.3: Random access timing advance.

The granularity of the timing advance is 16Ts ≃ 0.52µs and during this time radiowaves cover the distance of 156 m. This distance is the sum of downlink and up-link path, therefore one step of timing advance corresponds to the distance changebetween the UE and the eNB of 78 m.

7.1.4 Other cases

The actual timing advance is continuously adjusted by timing advance commandsent as MAC control element. The timing advance command MAC control elementis identified by MAC PDU subheader with LCID = 11101, as specified in 3GPP TS36.321.

The timing advance command field is 6 bits TA = 0, 1, 2, ..., 63 and indicates adjust-ment of the current NTA value (NTA,old) to the new NTA value (NTA,new) expressedin multiples of 16Ts, as specified by 3GPP TS 36.213:

NTA,new = NTA,old + 16(TA − 31). (7.3)

Adjustment of NTA value by a positive or a negative amount indicates advancing ordelaying the uplink transmission timing by a given amount respectively, as presentedin Figure 7.4. The maximum timing advance adjustment is equal to 16(63−31)Ts ≃16.7µs and corresponds to the distance change of 2.5 km.

For a timing advance command received on subframe n, the corresponding adjust-ment of the timing shall apply from the beginning of subframe n+6. When the UEsuplink transmissions in subframe n and subframe n + 1 are overlapped due to thetiming adjustment, the UE shall transmit complete subframe n and not transmitthe overlapped part of subframe n+ 1.

117


Figure 7.4: Adjustment of timing advance by MAC control element.

7.1.5 Maintenance of uplink time alignment

The UE has a configurable timer timeAlignmentTimer, which is used to control howlong the UE is considered uplink time aligned. The timer is sent in the SystemInformation Block Type 2.

TimeAlignmentT imer = {sf500, sf750, sf1280, sf1920, sf2560, sf5120,sf10240, infinity}.

(7.4)

Value in number of sub-frames. Value sf500 corresponds to 500 sub-frames, sf750corresponds to 750 sub-frames and so on (3GPP TS 36.331).

The UE starts the timeAlignmentTimer after random access response message isreceived and restarts the timer after each received timing advance command MACcontrol element.

When timeAlignmentTimer expires the UE shall:

• flush all HARQ buffers,

• notify RRC to release PUCCH/SRS,

• clear any configured downlink assignments and uplink grants.

To get time alignment a new the UE must initiate the random access process, seeFigure 7.5.

7.2 Random Access (RA)

From the physical layer perspective, the L1 RA procedure encompasses the transmis-sion of RA preamble and RA response. The remaining messages are scheduled fortransmission by the higher layer on the shared data channel and are not consideredpart of the L1 random access procedure.

A RA channel occupies 6 RBs in a subframe or set of consecutive subframes reservedfor RA preamble transmissions. The eNB is not prohibited from scheduling data inthe resource blocks reserved for PRACH transmission.

118

7.3 Resource allocation

Figure 7.5: UE time synchronisation.

Since the initial access attempt cannot be scheduled by the network, the RA pro-cedure is by definition contention based. Collisions may occur and an appropriatecontention-resolution scheme needs to be implemented.

The process of the RA is presented in Figure 7.6. UE sends the RA preamble withinitial power, which calculated based on the parameter preambleInitialReceivedTar-getPower and waits for the response in the response window configured by the pa-rameter ra-ResponseWindowSize. If the UE does not receive the RA response thenretransmits the RA increasing the power by powerRampingStep. The RA responseis recognised by its Random Access Radio Network Temporary Identity (RA-RNTI)and contains the allocation of the PDSCH, which includes the RA preamble iden-tity, timing and UL scheduling grant. The UE uses the granted PUSCH resourcesto send message 3, which contains RRC CONNECTION REQUEST command tothe eNB.


The resource allocation is sent to the UE on PDCCH. The downlink assignmentincludes:

• PDSCH resource indication,

• Transport format (applied coding and modulation),

• Transport block size,

• HARQ related information,

• MIMO related information (if applicable),

• PUCCH power order commands.

Resource indications can be of three different types: 0, 1, and 2 as described in3GPP TS 36.213, see also Figure 7.7. Type 0 and 1 use a bitmap to support non-contiguous allocation in the frequency domain. Type 0 does not allow to address asingle RB, therefore, type 0 is complemented by type 1. Type 2 allows to addressonly continuous RBs.

119


Figure 7.6: RA process.

Figure 7.7: DL resource allocation.

120


The Downlink Control Information (DCI) on the PDCCH has several supportedformats. The UE interprets the resource allocation field depending on the PDCCHDCI format detected. A resource allocation field in each PDCCH includes twoparts:

• resource allocation header,

• resource block assignment.

PDCCH DCI formats 1, 2, 2A and 2B with type 0 and PDCCH DCI formats 1,2, 2A and 2B with type 1 resource allocation have the same format and are dis-tinguished from each other via the single bit resource allocation header field whichexists depending on the downlink system bandwidth, where type 0 is indicated by 0value and type 1 is indicated otherwise. PDCCH with DCI format 1A, 1B, 1C and1D have a type 2 resource allocation while PDCCH with DCI format 1, 2, 2A and2B have type 0 or type 1 resource allocation. PDCCH DCI formats with a type 2resource allocation do not have a resource allocation header field. A UE shall dis-card PDSCH resource allocation in the corresponding PDCCH if consistent controlinformation is not detected.

7.3.1 Resource allocation type 0

In resource allocation of type 0 the RBs are grouped into P consecutive RBs calledResource Block Group (RBG). The reason for grouping RBs into RBG is to reducethe size of the bitmap used for resource allocation. P is than the size of the RBGand is a function of the system bandwidth, as specified in Table 7.1.

System bandwidth RBG size

NRBDL (P)

≤ 10 1

11-26 2

27-63 3

64-110 4

Table 7.1: Type 0 resource allocation RBG size vs. downlink system bandwidth.

The total number of RBGs for the downlink system bandwidth is given by

NRBG =

⌈NRB

DL

P

⌉(7.5)

One RBG may be of size lower than P. Assignment information includes a bitmapindicating the RBGs that are allocated to the scheduled UE. The bitmap is of sizeNRBG bits with one bitmap bit per RBG such that each RBG is addressable. TheRBG is allocated to the UE if the corresponding bit value in the bitmap is 1, theRBG is not allocated to the UE otherwise.

The resource allocation type 0 allows to allocate all RBs if needed, but it allows toallocate a single RB.

121



In resource allocations of type 1, the RBGs of size P are additionally divided intoP subsets. A UE may get assignment on RBs belonging to one subset only.

The resource allocation consists of a field, which indicates the selected subset, anda bitmap, which indicates allocated RBs within the set of RBs belonging to theselected subset.

The resource allocation type 1 does not allow to allocate all RBs to the UE, but itallows to allocate one RB, if needed.


In resource allocations of type 2, the resource block assignment information indicatesto a scheduled UE a set of contiguously allocated RBs.

Resource allocation type 2 allows to allocate all RBs to UE or one RB only if needed.However it does not allow for full allocation flexibility, because only continuous RBsmay be allocated.

7.4 MIMO

Multiple Input Multiple Output (MIMO) refers to the use of multiple antennas attransmitter and receiver side. The concept of multiple transmitting and receivingantennas is extensively used in LTE. MIMO systems form an essential part ofLTE in order to achieve the ambitious requirements for throughput and spectralefficiency. For the LTE downlink, a 2x2 configuration for MIMO is assumed asbaseline configuration, i.e. two transmit antennas at the base station and two receiveantennas at the terminal side. Configurations with four transmit or receive antennasare also foreseen and reflected in specifications.

The 3GPP TS 36.211 defines two downlink modes of MIMO, which were describedin sections 5.8.8 and 5.8.9:

• Spatial multiplexing

◦ without Cyclic Delay Diversity (CDD) – also called closed loop specialmultiplexing, which requires UE feedback concerning received phase shiftsfrom transmitting antennas,

◦ with CDD – also called open loop special multiplexing, which does notrequire UE feedback.

• Transmit diversity.

Depending on the MIMO mode that is used different gains can be achieved, seeFigure 7.8:

• With use of spatial multiplexing different data streams may be transmittedfrom antennas resulting in data rate multiplication.

• With use of spatial multiplexing modulation symbols from the same layer maybe transmitted from several antennas simultaneously. By adjusting the phase

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7.4 MIMO

of the modulation symbols transmitted from different antennas a constructiveinterference may be achieved in desired direction. This technique is calledbeamforming and it results in signal strength gain (beamforming gain).

• With use of transmit diversity the same data stream may be transmitted twiceand in different directions resulting in reduced signal fading.

Figure 7.8: Multi antenna possibilities.

In the following sections, a general description of spatial multiplexing and transmitdiversity is provided.

7.4.1 Spatial multiplexing

Spatial multiplexing allows for transmission of different data streams simultaneouslyon the same resource block(s) by exploiting the spatial dimension of the radio chan-nel. These data streams can belong to (see Figure 7.9):

• one single user – Single User MIMO (SU-MIMO), which increases thedata rate of one user and it may be applied for DL, because UE may havemultiple receiving antennas.

• different users – Multi User MIMO (MU-MIMO), which allows for in-crease of the overall capacity and it may be applied in the UL, because UEhas only one transmit antenna.

Figure 7.9: SU-MIMO and MU-MIMO.

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Figure 7.10 shows the principles of spatial multiplexing. In this figure, antennasTX0 and TX1 transmit different modulation symbols x(0) and x(1) respectively1.The signal received by antenna RX0 is a sum of signals transmitted by antennaTX0 and TX1. The signal transmitted by antenna TX0 is attenuated by pathlossh00 between antenna TX0 and RX0, while the signal transmitted by antenna TX1is attenuated by pathless h10 between antenna TX1 and RX0. In the same way, alsosignal received by antenna RX1 comes from antenna TX0 and TX1, but the trans-mitted signals are attenuated by path losses h01 and h11 respectively, see equationsin Figure 7.10. The path losses are measured by UE thanks to reference signals. Itis important that when one of the antennas transmits its reference signals then allothers antennas are silent. This lets the UE antennas measure the pathloss to thisparticular antenna.

Because all the path losses are known, as well as the measured signals z(0) and z(1),

the UE may solve the set of equations in Figure 7.10 for x(0) and x(1). This is how theUE is able to detect signals transmitted simultaneously from two antennas.

Figure 7.10: Spatial multiplexing principles.

Let us consider a system with more than two TX antennas. A signal from eachTX antenna can be considered as an unknown. Therefore the number of unknownsis equal to the number of TX antennas. On the other hand, for each RX antennaone equation may be created, so the number of equations is equal to the number ofreceiving antennas. To be able to solve a set of equations the number of equationsmust be equal to or more than the number of unknowns. Therefore having 4 TXantennas (unknowns) we must also have 4 receiving antennas (equations). Havingone or two receiving antennas would not let the UE to detect all 4 transmittedsignals.

Each antenna may transmit different layer. In spatial multiplexing, the number oflayers used for the transmission is equal to the bit rate multiplication. In order toachieve bit rate multiplication of 4, four layers must be transmitted simultaneously,which requires four TX and four RX antennas.

rmax = min{number of TX antennas, number of RX antennas} (7.6)

Spatial multiplexing is only possible if the radio channel allows for it. Depending onthe radio channel properties, it may be impossible to transmit 4 independent layers

1This is one of the spatial multiplexing transmission type. The complex numbers may also beweighted and added so, that each antenna actually transmits a combination of the symbols x(0) andx(1). This process is called precoding, see section 5.8.9.

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7.4 MIMO

between the transmitter and receiver. In this case the number of layers used for thetransmission may be less then rmax.

In the DL, the UE estimates the spatial properties of the radio channel by measuringthe DL reference symbols from different antenna ports. This estimation is reportedto the eNB, so that the eNB can use an appropriate number of layers an makeoptimal antenna mapping.

The report consists of CQI, Precoding Matrix Indicator (PMI) and RI (for detailssee section 7.5):

• CQI indicates the channel quality and is used whether or not spatial multi-plexing is used.

• RI indicates the number of useful layers and it must be equal to or less thenthe maximum number of layers.

RI ≤ rmax (7.7)

The maximum number of layers depends on the number of TX and RX anten-nas.

• PMI indicates the precoder matrix that the UE considers as the best (givesthe highest estimated Signal to Interference and Noise Ratio (SINR)).

7.4.2 Transmit diversity

Instead of increasing data rate or capacity, MIMO can be used to exploit diversityand increase the robustness of data transmission. Transmit diversity schemes arealready known from WCDMA release 99 and are also a part of LTE. Each transmitantenna transmits essentially the same stream of data, so the receiver gets replicasof the same signal, see Figure 7.11. This increases the signal to noise ratio atthe receiver side and thus the robustness of data transmission especially in fadingscenarios. Typically an additional antenna-specific coding is applied to the signalsbefore transmission to increase the diversity effect. Often, space-time coding isused.

Figure 7.11: Transmit diversity

7.4.3 Transmission modes

Switching between two MIMO transmission schemes of transmit diversity and spatialmultiplexing is possible depending on channel conditions as presented in Figure

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7.12.

Figure 7.12: Transmission mode 3: spatial multiplexing with large delay CDD ortransmit diversity.

In order to support different transmission schemes as well as switching betweendifferent transmission schemes, eight transmission modes have been defined by the3GPP TS 36.213, which are presented in Table 7.2. A transmission mode can useone or more transmission schemes. Typically, the transmission mode is set up at ses-sion establishment and does not changed during the session, while the transmissionscheme is dynamically decided every TTI.

7.4.4 MIMO antennas

The antennas used for MIMO should be uncorrelated. A suitable way of achievinguncorrelated antenna elements is to use polarisation diversity. A cross-polarisationantenna (XPol) is a common solution for 2x2 MIMO. Two cross-polarised antennas(XXPol) are used for 4x4 MIMO, see Figure 7.13.

Figure 7.13: MIMO antenna solutions.

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7.4 MIMO

Transmission

mode

DCI

formatSearch space Transmission scheme of PDSCH

1 1A Common andUE specific

Single-antenna port, port 0

1 UE specific Single-antenna port, port 0


Transmit diversity

1 UE specific Transmit diversity


Transmit diversity

2A UE specific Large delay CDD or Transmit diver-sity


Transmit diversity

2 UE specific Closed-loop spatial multiplexing orTransmit diversity


Transmit diversity

1D UE specific Multi-user MIMO


Transmit diversity

1B UE specific Closed-loop spatial multiplexing witha single transmission layer


If the number of PBCH antenna portsis one, Single-antenna port, port 0;otherwise Transmit diversity

1 UE specific Single-antenna port, port 5


If the number of PBCH antenna portsis one, Single-antenna port, port 0;otherwise Transmit diversity

2B UE specific Dual layer transmission, port 7 and 8or Single-antenna port, port 7 or 8

Table 7.2: PDSCH transmission scheme.

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7.5 UE reporting

The UE reporting is used to support optimal radio resource allocation for the down-link transmission towards UE. It means, the UE reporting is used by eNB to se-lect:

• Transport Format (TF) and

• frequency subbands.

The UE report may include indicators presented in Figure 7.14:

• Channel Quality Indicator (CQI), which is a measure of DL quality andit is used by eNodeB to choose the optimal modulation and coding rate fordownlink transmission.

• Rank Indicator (RI), which is the optimal number of layers for the DLtransmission for spatial multiplexing. For transmit diversity RI is equal toone.

• Precoding Matrix Indicator (PMI), which is used for precoding matrixselection when operating with MIMO.

Figure 7.14: UE reporting.

The time and frequency resources that can be used by the UE to report CQI, PMI,and RI are controlled by the eNB. The UE reporting is periodic or aperiodic.

• Periodic CQI/PMI, or RI reports are send by UE on PUCCH or PUSCH ifit collides in time domain with PUCCH.

• Aperiodic CQI/PMI, and RI reports are transmitted by UE on PUSCH ifthe conditions specified hereafter are met. For aperiodic CQI reporting, RI re-porting is transmitted only if configured CQI/PMI/RI feedback type supportsRI reporting.

Regarding the reported frequency band the CQI reporting is of two kinds:

• Frequency non-selective. One CQI value is reported by the UE for thewhole frequency band.

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7.5 UE reporting

• Frequency selective. UE provides several CQI values, one for each sub bandof the carrier. Frequency selective reporting is used for channel dependentscheduling and it is always aperiodic and transmitted on PUSCH only, seealso Table 7.3.

Scheduling mode

Periodic CQI Aperiodic CQI

reporting channels reporting channels

Frequency non-selective PUCCH

Frequency selective PUCCH PUSCH

Table 7.3: Physical Channels for Aperiodic or Periodic CQI reporting.

The reporting described in this section is not used for the best cell selection orhandover, as different event triggered reporting of Reference Signal Received Power(RSRP) and Reference Signal Received Quality (RSRQ) is specified to support UEmobility.

7.5.1 CQI definition

In Table 7.4 a list of 4-bit CQIs corresponding to the 16 possible combinations ofmodulation scheme and code rate is shown, which is specified by 3GPP TS 36.213.As can be seen in this table, CQI = 1 refers to the most robust transmission pa-rameters i.e. QPSK as modulation scheme and the lowest code rate of 78 userinformation symbols for 1024 transmitted symbols, which is selected for the worstchannel quality.

With increasing channel quality, higher order modulation schemes and higher coderates can be selected. The highest order of modulation and highest code rate, whichcan be selected are 64QAM and code rate of 948/1024 = 0.93 respectively andcorrespond to a CQI value of 15.

Depending on the SINR a the biggest CQI value is selected, which ensures that theBlock Error Rate (BLER) is less than 0.1.

7.5.2 Aperiodic CQI/PMI/RI reporting using PUSCH

A UE performs aperiodic CQI, PMI and RI reporting using the PUSCH upon re-ceiving a DCI format 0 or a Random Access Response Grant, if the respective CQIrequest field is set to 1 and is not reserved.

The possible reporting modes on the PUSCH are presented in Table 7.5. For eachof the transmission modes, see Table 7.2, only some of the the reporting modes aresupported as specified in Table 7.6. The aperiodic CQI reporting mode, which UEshould use is given by the parameter cqi-ReportModeAperiodic.

The UE may be configured to report one CQI value for the whole carrier band (socalled wideband CQI) or to divide the whole carrier band into several sub bands andprovide one CQI value for each band (subband reporting). The subband reportingmay be of two different kinds:

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Efficiency

CQI index Modulation Code rate x 1024 (information bits

(per symbol)

0 out of range

1 QPSK 78 0.1523

2 QPSK 120 0.2344

3 QPSK 193 0.3770

4 QPSK 308 0.6016

5 QPSK 449 0.8770

6 QPSK 602 1.1758

7 16QAM 378 1.4766

8 16QAM 490 1.9141

9 16QAM 616 2.4063

10 64QAM 466 2.7305

11 64QAM 567 3.3223

12 64QAM 666 3.9023

13 64QAM 772 4.5234

14 64QAM 873 5.1152

15 64QAM 948 5.5547

Table 7.4: 4-bit CQI Table.

PMI Feedback Type

No PMI Single PMI Multiple PMI

PUSCH

Wideband

(wideband CQI)Mode 1-2

CQI

Feedback

UE Selected

(subband CQI)Mode 2-0 Mode 2-2

Type Higher Layer configured


Table 7.5: CQI and PMI Feedback Types for PUSCH reporting modes.

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7.5 UE reporting

Transmission Reporting

mode mode

1 2-0, 3-0

2 2-0, 3-0

3 2-0, 3-0

4 1-2, 2-2, 3-1

5 3-1

6 1-2, 2-2, 3-1

7 2-0, 3-0

8 1-1, 2-2, 3-1

if the UE is configured

with PMI/RI reporting

2-0, 3-0


without PMI/RI reporting

Table 7.6: PUSCH reporting modes for different transmission modes.

• Higher layer-configured subband feedback,

• UE selected subband feedback.

In both cases a wideband average is computed and used as a reference. In addition,M subbands (M could be fixed or configured) of size k (see Table 7.7) are selectedand encoded differentially using two bits relative to the wide-band average.

In the case UE selected subband feedback the UE selects M subbands to report. TheUE internal procedure to select subbands is not specified but the selected subbandsshould correspond to the highest CQI values. The subbands selected by UE aresignalled using L = ⌈log2(NM )⌉ bits.

System Higher layer-configured UE-selected

Bandwidth Subband size k Subband size kM

NDLRB [RB] [RB]

6-7 N/A N/A N/A

8-10 4 2 1

11-26 4 2 3

27-63 6 3 5

64-110 8 4 6

Table 7.7: Subband size (k) vs. System Bandwidth.

7.5.3 Periodic CQI/PMI/RI reporting using PUCCH

A UE is semi-statically configured by higher layers to periodically feed back differentCQI, PMI, and RI on the PUCCH using the reporting modes given in Table 7.8 anddescribed below.

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PMI Feedback Type

No PMI Single PMI

PUCCH

CQI

Wideband

(wideband CQI)Mode 1-0 Mode 1-1

Feedback

Type

UE Selected


Table 7.8: CQI and PMI Feedback Types for PUCCH reporting modes.

For each of the transmission modes defined in Table 7.2, the reporting modes spec-ified in Table 7.9 are supported on PUCCH. The periodic CQI reporting mode isgiven by the parameter cqi-FormatIndicatorPeriodic, which is configured by higher-layer signalling.

The periodicity of the QCI/PMI reporting is defined by the parameter cqi-PUCCH-ResourceIndex (TS 36.331) and can be set between 2 ms to 160 ms for FDD (TS36.213). The periodicity of RI reporting is set by the parameter ri-ConfigIndex andcan be set between 1 to 32 ms.

Transmission Reporting

mode mode

1 1-0, 2-0

2 1-0, 2-0

3 1-0, 2-0

4 1-1, 2-1

5 1-1, 2-1

6 1-1, 2-1

7 1-0, 2-0

8 1-1, 2-1


with PMI/RI reporting

1-0, 2-0


without PMI/RI reporting

Table 7.9: PUCCH reporting modes for different transmission modes.

7.6 Modulation order and transport block size de-termination

The DL Modulation and Coding Scheme (MCS) is selected by eNB. The eNBdecision may be based on CQI feedback and buffer content. The eNB algorithm usedfor modulation and transport block size determination is often referred to as LA.Rapid interference variations make it difficult to predict the link quality accurately,and select MCS based on such knowledge. Therefore, decision which MCS to used

132

7.6 Modulation order and transport block size determination

is based on averaged link quality and next adjusted depending if the objective is toprovide high throughput or low delay:

• If the objective is to provide low delay (few retransmissions), a margin tothe interference variations can be included. This however leads to limitedthroughput, as often an unnecessary robust MCS is used.

• To reach high throughput, a low margin (even negative) is used. This willinstead lead to a larger number of retransmissions, and hence a larger delay.The risk of throughput loss or large delays in case of negative margins isreduced by the use of incremental redundancy for retransmissions.

7.6.1 Modulation determination

The eNB decision, which modulation and coding is used for the PDSCH, is commu-nicated to the UE by the 5-bit“modulation and coding scheme” field IMCS in theDCI presented in Table 7.10.

7.6.2 Transport block size determination

The Transport Blok Size (TBS), that is the number user bits in the transport block,is determined depending on the value of IMCS in the following way:

• For 0 ≤ IMCS ≤ 28 the UE determines the TBS index ITBS using Table 7.10.

◦ For transport blocks not mapped to two-layer spatial multiplexing, theTBS is given by the (ITBS, NPRB) entry of Table 7.11.

◦ For transport block mapped to two-layer spatial multiplexing:

for 1 ≤ NPRB ≤ 55, the TBS is given by the (ITBS, 2NPRB) entryof Table 7.11. It means that the transport block is twice as muchas in case of one-layer spatial multiplexing, transmit diversity or noMIMO.

for 56 ≤ NPRB ≤ 110 there is different way of deriving the TBS.It results in the TBS a little less then twice as much as in case ofone-layer spatial multiplexing, transmit diversity or no MIMO.

• For 29 ≤ IMCS ≤ 31, the TBS is assumed to be as determined from DCItransported in the latest PDCCH for the same transport block using 0 ≤IMCS ≤ 28.

For example, if the IMCS = 28 and NPRB = 100 then from Table 7.10 the ITBS = 26and from Table 7.11 the TBS = 75376 bits. It means that the transport block willbe sent over 100 RBs and will contains 75376 user data bits. Taking into accountthat the transport block transmission time is 1 ms, the momentary MAC layer userthroughput will be 75376 bit

1ms ≃ 75Mbps and it is the maximum possible throughputper one layer in LTE. In two layer spatial multiplexing the throughput will be twicebigger, that is 300 Mbps.

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MSC index Modulation order TBS index

IMCS Qm ITBS

0 2 0

1 2 1

2 2 2

3 2 3

4 2 4

5 2 5

6 2 6

7 2 7

8 2 8

9 2 9

10 4 9

11 4 10

12 4 11

13 4 12

14 4 13

15 4 14

16 4 15

17 6 15

18 6 16

19 6 17

20 6 18

21 6 19

22 6 20

23 6 21

24 6 22

25 6 23

26 6 24

27 6 25

28 6 26

29 2

30 4 reserved

31 6

Table 7.10: Modulation and TBS index table for PDSCH.

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7.6 Modulation order and transport block size determination

ITBSNPRB

1 2 3 4 5 6 7 98 99 100

0 16 32 56 88 120 152 176 2728 2728 2792

1 24 56 88 144 176 208 224 3624 3624 3624

2 32 72 144 176 208 256 296 4392 4392 4584

3 40 104 176 208 256 328 392 5736 5736 5736

4 56 120 208 256 328 408 488 6968 6968 7224

5 72 144 224 328 424 504 600 8760 8760 8760

6 328 176 256 392 504 600 712 10296 10296 10296

7 104 224 328 472 584 712 840 11832 12216 12216

8 120 256 392 536 680 808 968 13536 14112 14112

9 136 296 456 616 776 936 1096 15264 15840 15840

10 144 328 504 680 872 1032 1224 16992 17568 17568

11 176 376 584 776 1000 1192 1384 19848 19848 19848

12 208 440 680 904 1128 1352 1608 22152 22920 22920

13 224 488 744 1000 1256 1544 1800 25456 25456 25456

14 256 552 840 1128 1416 1736 1992 28336 28336 28336

15 280 600 904 1224 1544 1800 2152 30576 30576 30576

16 328 632 968 1288 1608 1928 2280 31704 31704 32856

17 336 696 1064 1416 1800 2152 2536 35160 35160 36696

18 376 776 1160 1544 1992 2344 2792 39232 39232 39232

19 408 840 1288 1736 2152 2600 2984 42368 42368 43816

20 440 904 1384 1864 2344 2792 3240 45352 46888 46888

21 488 1000 1480 1992 2472 2984 3496 48936 48936 51024

22 520 1064 1608 2152 2664 3240 3752 52752 52752 55056

23 552 1128 1736 2280 2856 3496 4008 57336 57336 57336

24 584 1192 1800 2408 2984 3624 4264 59256 61664 61664

25 616 1256 1864 2536 3112 3752 4392 61664 63776 63776

26 712 1480 2216 2984 3752 4392 5160 73712 73712 75376

Table 7.11: Transport block size table.

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7.7 UL power control

The 3GPP TS 36.213 specifies algorithms of power control on PUCCH and PUSCH.Both algorithms are similar. The standard specifies open loop and closed loop powercontrol algorithms for PUCCH and PUSCH:

• In open loop power control the UE calculates the output power based on down-link measurements and controlling parameters sent by eNB, see Figure 7.15.

Figure 7.15: Open loop power control.

• In closed loop power control additional correction of the open loop power con-trol algorithm is provided to the UE. The correction provided by eNB indicatesif the UE should increase or decrease its transmit power compared to the openloop algorithm, see Figure 7.16.

Figure 7.16: Closed loop power control.

7.7.1 PUSCH power control

The UE calculates its output, which will transmit in a subframe i, on the bases ofthe below formula. The formula is common for open loop and closed loop powercontrol. The difference is, that in closed loop power control the eNB provides the

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UE with a Transmit Power Control (TPC) command that includes δPUSCH. TheδPUSCH is used to calculate the closed loop power adjustment f(i):

PPUSCH(i) = min{PCMAX,

10 log10(MPUSCH(i)) + P0 PUSCH(j) + α(j) · PL+∆TF(i) + f(i)} [dBm](7.8)

where,

• PCMAX is the maximum allowed power by the terminal and depends on theUE power class,

• MPUSCH(i) is the bandwidth of the PUSCH resource assignment expressed innumber of resource blocks valid for subframe i.

• P0 PUSCH(j) is the parameter composed of the sum of a cell specific nominalcomponent P0 NOMINAL PUSCH(j) sent in the SIB2 for j = 0 and 1 and a UEspecific component P0 UE PUSCH(j) sent in dedicated signalling for layers forj = 0 and 1.

◦ For PUSCH (re)transmissions corresponding to a semi-persistent grantthen j = 0.

◦ For PUSCH (re)transmissions corresponding to a dynamic scheduled grantthen j = 1.

◦ For PUSCH (re)transmissions corresponding to the random access re-sponse grant then j = 2 and:

P0 UE PUSCH(2) = 0

P0 NOMINAL PUSCH(2) = P0 PRE +∆PREAMBLE Msg3,(7.9)

where the parameterPREAMBLE INITIAL RECEIVED TARGET POWER (P0 PRE)and ∆PREAMBLE Msg3 are signalled from higher layers.

• α is the pathloss compensation factor.For j = 0 or 1, α ∈ {0, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1} is a 3-bit cell specific param-eter sent in SIB2.For j = 2, α = 0.

• PL is the downlink pathloss estimate calculated in the UE in dB andPL = referenceSignalPower − higher layer filtered RSRP,where referenceSignalPower is transmitted in SIB2.

• ∆FT(i) is the Transport Format dependent compensation offset. The value ofthe offset depends on the UE specific parameter deltaMCS-Enabled providedby higher layers.

• f(i) is the current closed loop PUSCH power control adjustment. There aretwo methods of the power control adjustments: accumulated and absolute.User specific parameter Accumulation-enabled informs the UE which one touse. In both cases the power control adjustment f(i) depends on the UEspecific correction value δPUSCH, also referred to as TPC command. The TPCcommand is transmitted on PDCCH and is used to calculate the power control

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adjustment differently for accumulated and absolute method:

f(i) = f(i− 1) + δPUSCH(i−KPUSCH) for accumulated

f(i) = δPUSCH(i−KPUSCH) for absolute(7.10)

◦ KPUSCH is equal 4 for FDD and for TDD is equal 4, 6 or 7 dependingon the UL/DL TDD configuration.

◦ δPUSCH is the TPC command given in dB. δPUSCH values are signalledon the PDCCH with DCI format 0 or jointly coded with other TPCcommands in PDCCH with DCI format 3/3A whose CRC parity bits arescrambled with TPC-PUSCH-RNTI. The δPUSCH values signalled on thePDCCH with DCI format 0 are given in Table 7.12. The δPUSCH valuessignalled on the PDCCH with 3/3A are one of SET1 given in Table 7.12or SET2 given in Table 7.13 as determined by the parameter TCP-Indexprovided by higher layers.

TCP Command Field

in DCI format 0/3

Accumulated

δPUSCH [dB]

Absolute

δPUSCH [dB]

only DCI format 0

0 -1 -4

1 0 -1

2 1 1

3 3 4

Table 7.12: Mapping of TPC Command Field in DCI format 0/3 to absolute andaccumulated δPUSCH values.

TCP Command Field Accumulated

in DCI format 3A δPUSCH

0 -1

1 1

Table 7.13: Mapping of TPC Command Field in DCI format 3A to accumulatedδPUSCH values.

In the accumulated mode:

• If UE has reached maximum power, positive TPC commands are not accumu-lated.

• If UE has reached minimum power, negative TPC commands shall not accu-mulated.

• UE reset accumulation:

◦ when P0 UE PUSCH value is changed by higher layers.

◦ when UE receives random access response.

In the absolute mode:

• f(i) = f(i−1) for a subframe where no PDCCH with DCI format 0 is decoded.

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For both accumulated and absolute method the first value is set as follows:

f(0) = 0 if P0 UE PUSCH value is changed

f(0) = ∆Prampup + δmsg2 other cases(7.11)

• δmsg2 is the TPC command indicated in the random access response,

• ∆rampup is provided by higher layers and corresponds to the total power ramp-up from the first to the last preamble.

Figures 7.17 and 7.18 present accumulated and absolute closed loop power controladjustment.

Figure 7.17: Accumulated method of the closed loop power control adjustment.

Figure 7.18: Absolute method of the closed loop power control adjustment.

7.7.2 PUSCH power control example

Figure 7.19 illustrates the open loop power control for the path loss compensationparameter α = 1 (full path loss compensation). For α = 1 then drop of the RSRPby 10 dB, results in increase of the UE transmit power by 10 dB. This UE powerincrease fully compensate the path loss increase and leads to constant PSDRX at

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the eNB in accordance to the setting of the parameter P0 PUSCH = −109 dBm.But for far enough distance UE reaches its maximum transmit power and it cannotanymore compensate the path loss increase. In this example it happens for theRSRP equal to −117 dBm. Therefore, when the UE moves further from the eNBand RSRP drops below −117 dBm, the PSDRX at the eNB drops below the designthreshold P0 PUSCH = −109 dBm resulting in throughput reduction. It should alsobe noted, that, as long as the PSDRX at the eNB is equal to the design thresholdP0 PUSCH = −109, the UE UL throughput is constant regardless of the UE locationin a cell.

Figure 7.19: Transmitted power and signal at eNB as a function of the RSRPfor the following parameters setting: PCMAX = 23 dBm, MPUSCH = 1, P0 PUSCH =−109 dBm, α = 1, referenceSignalPower = 15 dBm.

Figure 7.20 shows dependence of PSDRX and the TBS on the number of allocatedRBs to the UE. For low number of allocated RBs the UE is able to keep requiredtarget PSDRX in accordance with the parameter P0 PUSCH = −109 dBm. To do so,the UE must transmit more power when more RBs are allocated to it. Thereforethe transmitted power of the UE grows linearly with the number of allocated RB.Accordance to the power control algorithm, UE transmits the same power for eachRB. Because the target PSDRX is achieved the same coding and modulation is usedand the TBS (that is also throughput) grows linearly with the number of allocatedRBs.

At some number of RBs the maximum power of the UE is achieved and the UE can-not further increase its power. Therefore the output power of the UE is distributedevenly between the transmitted RBs leading to the power per RB below the targetPSDRX. To handle lower signal-to-interference ratio at the eNB, the eNB’s link

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adaptation algorithm decides about more robust coding or modulation to be usedby UE for the UL transmission. TBS still grows due to more RBs allocated, butdue to more robust coding and modulation the grow is less then linear.

Figure 7.20: The target PSDRX and the TBS.

P0 PUSCH

In this example the parameter P0 PUSCH = −109 dBm. This section show the processof the parameters calculation.

The throughput depends on the bandwidth, which is used for the signal transmis-sion, and SINR. Stronger the signal above noise and interference level, bigger thethroughput. This theoretical relation is know as Snannon theorem:

Throughput = B log2(1 + SINR), (7.12)

where B is the bandwidth used for the transition.

Let us assume that the wanted UL SINR, which provides satisfactory throughput,is SINRUL = −2 dB and the expected UL noise rise due to UEs transmitting inneighbouring cells is Imarg,UL = 12dB. With these assumptions, and also assuminga typical noise figure of the eNB, the minimum value of P0 PUSCH can be calculatedas presented in Table 7.14.

141


No. Element Value

1 Boltzmann constant, k 1.3806·10−23 J/K

2 Temperature, T 290 K

3 Thermal noise power density, kT 4.00 · 10−21 J

4 Bandwidth, BRB 180000 Hz

5 eNB noise figure, Nf 5 dB

6 Thermal noise, NRB,UL = 10 log(kT ·BRB1mW

)+Nf -119.4 dBm

7 Interference margin, Imarg,UL 12 dB

8 SINRUL -2 dB

9 SeNB = NRB,UL + Imarg,UL + SINRUL -109.4 dBm

10 P0 PUSCH ≥ SeNB -109 dBm

Table 7.14: P0 PUSCH calculation.

referenceSignalPower

In this example the parameter and the referenceSignalPower = 15dBm. Thissections shows the process of the parameter calculation.

No. Element Value

1 eNB transmit power, PeNB 40 W

2 Number of RBs in the carrier bandwidth, NRB 50 RB

3 Antenna feeder loss, Lf 3 dB

4 referenceSignalPower = 10 log PeNB/(12NRB)1mW − Lf 15 dBm

Table 7.15: referenceSignalPower calculation.

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8 LTE mobility

This chapter describes UE mobility in LTE with a focus on the algorithms, that areused to choose the best cell to serve the UE.

In the RRC IDLE the cell selection algorithm S and cell reselection algorithm R areused by the UE to choose a cell. Also the PLMN selection algorithm is presented inthis chapter.

In RRC CONNECTED the eNB chooses a cell, but its decision is supported bythe UE measurements. The UE measurement reports are triggered by events. Forexample, the UE may send a measurement report when it finds a neighbouring cellthat is better than serving. This event may be used by the eNB to trigger a handoverto the reported better neighbouring cell. This chapter also presents a flow graph ofthe handover process.

8.1 Idle mode mobility

In idle mode (RRC IDLE) the UE has no connection to the radio network, i.e.no RRC connection is established. The purpose of keeping UE in idle mode is tominimise the resource usage both for the UE and for the network. Yet the UE shouldstill be able to access the system and be reached by the system with acceptabledelays.

In idle mode the UE:

• Monitors system information, that system and cell specific parameters trans-mitted to all UEs in a cell.

• Selects the PLMN.

• Selects a suitable cell of the selected PLMN to camp on by using the cellselection algorithm.

• After the cell selection the UE attaches and registers to the CN supported bythe PLMN. This process is called location registration.

• Performs cell reselection based on radio measurements. Cell reselection makessure that the UE is always camping on the cell that gives the highest proba-bility for successful establishment of a connection. The cell reselection processmay imply a change of the RAT i.e. (GSM/ GPRS/WCDMA/CDMA2000LTE).

• Monitors paging.

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• May initiate a connection by sending random access.

Figure 8.1 illustrates relation between PLMN selection, cell selection and reselectionand location registration according to the TS 36.304.

Figure 8.1: Overall idle mode process.

8.1.1 PLMN selection

The PLMN selection process aims at finding an operator, where the UE can find asuitable cell and access available services. The PLMN selection process is describedin TS 22.011.

The following concepts are use in the PLMN selection process:

• PLMN selector lists.

• Equivalent HPLMN (EHPLMN).

• Forbidden TAs or LAs lists.

The above concepts are explained in the next sections and next the actual PLMNselection algorithm is described.

PLMN selector lists

There are two PLMN priority lists stored on the Universal Subscriber Identity Mod-ule (USIM):

• Operator Controlled PLMN Selector list.

• User Controlled PLMN Selector list.

Both PLMN selector lists may contain a list of preferred PLMNs in priority order. Itshall be possible to have an associated access technology identifier e.g., E-UTRAN,

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UTRAN, or GERAN associated with each entry in the PLMN selector lists. APLMN in a selector list may have multiple occurrences with different access tech-nology identifiers. The UE ignores those PLMN + access technology entries in thePLMN selector lists where the associated access technology is not supported by theUE.

EHPLMN

It shall be possible to handle cases where one network operator accepts access fromaccess networks with different network IDs. It shall also be possible to indicate tothe UE that a group of PLMNs are equivalent to the registered PLMN regardingPLMN selection, cell selection/reselection and handover.

It shall be possible for the home network operator to identify alternative networkIDs as the Home PLMN (HPLMN). It shall be possible for the home networkoperator to store in the USIM an indication to the UE that a group of PLMNs aretreated as the HPLMN regarding PLMN selection. Any PLMN to be declared as anequivalent to the HPLMN shall be present within the EHPLMN list and is called anEHPLMN. The EHPLMN list replaces the HPLMN derived from the InternationalMobile Subscriber Identity (IMSI). When the EHPLMN list is present, any PLMNin this list shall be treated as the HPLMN in all the network and cell selectionprocedures.

Forbidden TAs and LAs for roaming

When a registration attempt by the UE is rejected by a network, the UE stores thetracking area identity or the location area identity in the list of “forbidden TAs orLAs for roaming” respectively. The lists of forbidden TAs and LAs are maintainedin the UE to avoid unnecessary registration attempts.

PLMN selection algorithm

Depending on the user setting the UE follows one of the following procedures fornetwork selection:

• Automatic network selection mode.

The default behaviour for a UE is to select the last registered PLMN.

As an alternative option to this, if the UE is in automatic network selectionmode and it finds coverage of the HPLMN or any EHPLMN, the UE mayregister on the HPLMN (if the EHPLMN list is not present) or the highestpriority EHPLMN of the available EHPLMNs (if the EHPLMN list is present)and not return to the last registered PLMN. If the EHPLMN list is presentand not empty, it shall be used. The operator shall be able to control byUSIM configuration whether an UE that supports this option shall follow thisalternative behaviour.

The UE selects and attempts registration on other PLMNs, if available andallowable, if the location area is not in the list of “forbidden LAs for roaming”and the tracking area is not in the list of “forbidden TAs for roaming”, in thefollowing order, which is also illustrated in Figure 8.2:

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1. An EHPLMN, if the EHPLMN list is present, or the HPLMN (derivedfrom the IMSI), if the EHPLMN list is not present for preferred accesstechnologies, in the order specified. In the case that there are multipleEHPLMNs present then the highest priority EHPLMN shall be selected.

2. Each entry in the User Controlled PLMN Selector list with accesstechnology data field in the SIM/USIM (in priority order).

3. Each entry in the Operator Controlled PLMN Selector list withaccess technology data field in the SIM/USIM (in priority order).

4. Other PLMN/access technology combinations with sufficient receivedsignal quality in random order. A PLMN is considered to have suf-ficient received signal quality if:

◦ for LTE cell: RSRP ≥ −110 dBm (TS 36.304),

◦ for WCDMA FDD cell: RSCP ≥ −95 dBm (TS 25.304),

◦ for WCDMA TDD cell: RSCP ≥ −84 dBm (TS 25.304),

◦ for GSM cell: rxlev > −85 dBm (TS 43.022).

5. All other PLMN/access technology combinations in order of decreas-ing signal quality.

• Manual network selection mode.

1. A registered PLMN is selected if available.

2. A list of available PLMNs is presented to a user and the user selects oneof the PLMNs manually. If the registration cannot be achieved on theselected PLMN, the UE shall indicate “No Service”. The user may thenselect and attempt to register on another or the same PLMN.

Once the UE has selected a PLMN, the cell selection procedure shall be performedin order to select a suitable cell of that PLMN to camp on.

8.1.2 Cell selection

After a UE has switched on and a PLMN has been selected, the cell selection processtakes place. This process allows the UE to select a suitable cell where to camp on inorder to access available services. In this process the UE can use stored information(stored information cell selection) or not (initial cell selection).

Description

To select a cell the UE uses one of the following two cell selection procedures:

1. Initial cell selection.

This procedure requires no prior knowledge of which RF channels are EvolvedUniversal Terrestrial Radio Access (E-UTRA) carriers. The UE shall scanall RF channels in the E-UTRA bands according to its capabilities to finda suitable cell. On each carrier frequency, the UE need only search for thestrongest cell. Once a suitable cell is found this cell shall be selected.

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Figure 8.2: Automatic PLMN selection process.

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2. Stored information cell selection.

This procedure requires stored information of carrier frequencies and optionallyalso information on cell parameters, from previously received measurementcontrol information elements or from previously detected cells. Once the UEhas found a suitable cell the UE shall select it. If no suitable cell is found theinitial cell selection procedure shall be started.

NOTE: Priorities between different frequencies or RATs provided to the UE bysystem information or dedicated signalling are not used in the cell selection pro-cess.

Cell selection criterion

The cell selection criterion S is fulfilled when:

S > 0 (8.1)

where

S = Qmeas,s − (q-RxLevMin+ q-RxLevMinOffset)− Pcompensation (8.2)

where

S – cell selection level value [dB].

Qmeas,s – measured cell RX level value RSRP [dBm].

q-RxLevMin – minimum required RX level [dBm] in the cell sent in SIB1(Table A.2).

q-RxLevMinOffset – offset [dB] to the signalled q-RxLevMin taken into account inthe Srxlev evaluation as a result of a periodic search for ahigher priority PLMN while camped normally in a VPLMN.Sent in SIB1 (Table A.2).

Pcompensation = max(p-Max− PPowerClass, 0) [dB].

p-Max – maximum TX power level [dBm] an UE may use when trans-mitting on the uplink in the cell. The parameter is sent inSIB1 (Table A.2).

PPowerClass – maximum RF output power of the UE according to the UEpower class [dBm].

8.1.3 Cell reselection

Following rules are used by the UE to limit needed measurements:

• If the cell parameter S-IntraSearch is sent in the SIB3 of the serving cell andSs > S-IntraSearch, UE may choose to not perform intra-frequency measure-ments.

• If Ss ≤ S-IntraSearch, or S-IntraSearch is not sent in the serving cell UE shallperform intra-frequency measurements.

The Ss is the S value of the serving cell as specified by formula 8.2.

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Cell reselection criteria

The reselection criterion discussed in this section applies for:

• Intra-frequency cell re-election.

• Equal priority inter-frequency cell reselection.

All cells that fulfill the cell selection criterion S (formula 8.1) are ranked accordingto the R criteria specified as follows:

Rs = Qmesa,s + q-Hyst

Rn = Qmesa,n −Qoffset

(8.3)

Rs – ranking criteria for serving cell [dBm].

Rn – ranking criteria for neighbouring cell [dBm].

Qmeas,s – averaged measured RSRP value for serving cell [dBm].

Qmeas,n – averaged measured RSRP value for neighbouring cell [dBm].

q-Hyst – cell reselection hysteresis parameter [dB] broadcast in the SIB3of the serving cell (Table A.4).

Qoffset =

{q-OffsetCells,n for intra LTE frequency neighbour

q-OffsetFreq+ q-OffsetCells,n for inter LTE frequency neighbour

(8.4)

q-OffsetCells,n – neighbour relation specific offset [dB] sent in SIB4 for intraLTE frequency neighbouring cells (Table A.5) and in SIB5 forinter LTE frequency neighbouring cells (Table A.6).

q-OffsetFreq – frequency specific offset [dB] for equal priority E-UTRAN fre-quencies sent in SIB5 (Table A.6).

The UE reselects the new cell, if the cell reselection criteria are fulfilled during thetime interval t-ReselectionEUTRA, which is illustrated in Figure 8.3.

Mobility states of UE

Besides normal mobility state a high mobility state and a medium mobility state areapplicable. Reduced value of q-Hyst and t-ReselectionEUTRA are applied for UE inhigh or medium mobility state, which result in earlier reselections compared to thenormal mobility state:

• High mobility state. UE enters high mobility state if number of cell rese-lections during time period t-Evaluation exceeds n-CellChangeHigh.

Hysteresis and reselection time for high mobility state:

q-Hyst+ q-HystSF(sf-High)

t-ReselectionEUTRA · t-ReselectionEUTRA-SF(sf-High)(8.5)

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Figure 8.3: Cell reselection criterion.

• Medium mobility state. UE enters medium mobility stets if number of cellreselections during time period t-Evaluation exceeds n-CellChangeMedium andnot exceeds n-CellChangeHigh.

Hysteresis and reselection time for medium mobility state:

q-Hyst+ q-HystSF(sf-Medium)

t-ReselectionEUTRA · t-ReselectionEUTRA-SF(sf-Medium)(8.6)

q-HystSF and t-ReselectionEUTRA-SF are transmitted in the SIB3 of the serv-ing cell (see Table A.4).

8.2 Connected mode mobility

In RRC CONNECTED, the eNB controls UE mobility, i.e. the eNB decides whenthe UE shall move to which cell (which may be on another frequency or RAT).For network controlled mobility in RRC CONNECTED, handover is the only pro-cedure that is defined. The eNB triggers the handover procedure e.g. based on radioconditions and load.

There are two cases of EPS handovers:

• X2 handover.

The HO procedure is performed without EPC involvement, i.e. preparationmessages are directly exchanged between the eNBs. The release of the re-sources at the source side during the HO completion phase is triggered by theeNB.

• S1 handover.

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The HO procedure is performed with MME involvement. The MME and S-GWmay be reallocated.

8.2.1 X2 handover

The Figure 8.4 depicts the basic handover scenario where neither MME nor S-GWchanges (TS 36.300):

Figure 8.4: X2 handover.

1. To facilitate the handover decision the source eNB configures the UE to per-form measurement reporting.

2. UE is triggered to send MEASUREMENT REPORT by the rules set byi.e. system information, specification etc.

3. Source eNB makes decision based on MEASUREMENT REPORT and RRMinformation to hand off UE. The network may also initiate handover blindly,i.e. without having received measurement reports from the UE.

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4. The source eNB issues a HANDOVER REQUEST message to the target eNBpassing necessary information to prepare the HO at the target side (UE X2signalling context reference at source eNB, UE S1 EPC signalling contextreference, target cell ID, KeNB∗ , RRC context including the C-RNTI of the UEin the source eNB, AS-configuration, E-RAB context and physical layer ID ofthe source cell + MAC for possible Radio Link Failure (RLF) recovery). UEX2/UE S1 signalling references enable the target eNB to address the sourceeNB and the EPC. The E-RAB context includes necessary Radio NetworkLayer (RNL) and Transport Network Layer (TNL) addressing information,and QoS profiles of the E-RABs.

5. Admission Control may be performed by the target eNB depending on thereceived E-RAB QoS information. The target eNB configures the requiredresources according to the received E-RAB QoS information and reserves aC-RNTI and optionally a RACH preamble.

6. Target eNB prepares HO with L1/L2 and sends the HANDOVER REQUESTACKNOWLEDGE to the source eNB. The HANDOVER REQUEST AC-KNOWLEDGE message includes a transparent container to be sent to theUE as an RRC message to perform the handover. The container includes anew C-RNTI, target eNB security algorithm identifiers for the selected securityalgorithms, may include a dedicated RACH preamble, and possibly some otherparameters i.e. access parameters, SIBs, etc. The HANDOVER REQUESTACKNOWLEDGE message may also include RNL/TNL information for theforwarding tunnels, if necessary.

NOTE: As soon as the source eNB receives the HANDOVER REQUEST AC-KNOWLEDGE, or as soon as the transmission of the handover commandis initiated in the downlink, data forwarding may be initiated.

7. The target eNB generates the RRC message to perform the handover, i.e RRC-ConnectionReconfiguration message including the mobilityControlInformation,to be sent by the source eNB towards the UE. The UE does not need to delaythe handover execution for delivering the HARQ/ARQ responses to sourceeNB.

8. The source eNB sends the SN STATUS TRANSFER message to the targeteNB to convey the uplink PDCP Sequence Number (SN) receiver status andthe downlink PDCP SN transmitter status of E-RABs for which PDCP statuspreservation applies (i.e. for RLC AM). The uplink PDCP SN receiver statusincludes at least the PDCP SN of the first missing UL SDU and may includea bit map of the receive status of the out of sequence UL SDUs that theUE needs to retransmit in the target cell, if there are any such SDUs. Thedownlink PDCP SN transmitter status indicates the next PDCP SN that thetarget eNB shall assign to new SDUs, not having a PDCP SN yet. The sourceeNB may omit sending this message if none of the E-RABs of the UE shall betreated with PDCP status preservation.

9. After receiving the RRCConnectionReconfiguration message including the mo-bilityControlInformation, UE performs synchronisation to target eNB and ac-cesses the target cell via RACH, following a contention-free procedure if adedicated RACH preamble was indicated in the mobilityControlInformation,

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or following a contention-based procedure if no dedicated preamble was indi-cated. UE derives target eNB specific keys and configures the selected securityalgorithms to be used in the target cell.

10. The target eNB responds with UL allocation and timing advance.

11. When the UE has successfully accessed the target cell, the UE sends the RRC-ConnectionReconfigurationComplete message (C-RNTI) to confirm the han-dover, along with an uplink Buffer Status Report, whenever possible, to thetarget eNB to indicate that the handover procedure is completed for the UE.The target eNB verifies the C-RNTI sent in the RRCConnectionReconfigura-tionComplete message. The target eNB can now begin sending data to theUE.

12. The target eNB sends a PATH SWITCH message to MME to inform that theUE has changed cell. Observe, that so far the handover process was carriedout without interaction with MME and S-GW.

13. The MME sends an UPDATE USER PLANE REQUEST message to theS-GW.

14. The S-GW switches the downlink data path to the target side. The S-GWsends one or more “end marker” packets on the old path to the source eNBand then can release any UP/TNL resources towards the source eNB.

15. Serving Gateway sends an UPDATE USER PLANE RESPONSE message toMME.

16. The MME confirms the PATH SWITCH message with the PATH SWITCHACKNOWLEDGE message.

17. By sending UE CONTEXT RELEASE, the target eNB informs success of HOto source eNB.

18. Upon reception of the UE CONTEXT RELEASE message, the source eNBcan release radio and CP related resources associated to the UE context. Anyongoing data forwarding may continue.

8.2.2 Event triggered reporting

The UE reports measurement information in accordance with the measurement con-figuration as provided by the eNB. eNB provides the measurement configuration ap-plicable for a UE in RRC CONNECTED by means of dedicated signalling, i.e. usingthe RRCConnectionReconfiguration message, which is step 1 in Figure 8.4.

The UE can be requested to perform the following types of measurements (TS36.331):

• Intra frequency measurements: measurements at the downlink carrier fre-quency of the serving cell.

• Inter frequency measurements: measurements at frequencies that differ fromthe downlink carrier frequency of the serving cell.

• Inter RAT measurements of UTRAN frequencies.

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• Inter RAT measurements of GERAN frequencies.

• Inter RAT measurements of CDMA2000 High Rate Packet Data (HRPD) orCDMA2000 1x Radio Transmission Technology (1xRTT) frequencies.

The measurement configuration includes the following parameters (TS 36.331):

1. Measurement objects: The objects on which the UE shall perform themeasurements.

• For intra frequency and inter frequency measurements a measurementobject is a single E-UTRAN carrier frequency. Associated with this car-rier frequency, E-UTRAN can configure a list of cell specific offsets anda list of “blacklisted” cells. Blacklisted cells are not considered in eventevaluation or measurement reporting.

• For inter RAT UTRAN measurements a measurement object is a set ofcells on a single UTRAN carrier frequency.

• For inter RAT GERAN measurements a measurement object is a set ofGERAN carrier frequencies.

• For inter RAT CDMA2000 measurements a measurement object is a setof cells on a single (HRPD or 1xRTT) carrier frequency.

2. Reporting configurations: A list of reporting configurations where eachreporting configuration consists of the following:

• Reporting criterion: The criterion that triggers the UE to send a measure-ment report. This can either be periodical or a single event description.

• Reporting format: The quantities that the UE includes in the measure-ment report and associated information (e.g. number of cells to report).

3. Measurement identities: A list of measurement identities where each mea-surement identity links one measurement object with one reporting configura-tion. By configuring multiple measurement identities it is possible to link morethan one measurement object to the same reporting configuration, as well as tolink more than one reporting configuration to the same measurement object.The measurement identity is used as a reference number in the measurementreport.

4. Quantity configurations: One quantity configuration is configured per RATtype. The quantity configuration defines the measurement quantities and as-sociated filtering used for all event evaluation and related reporting of thatmeasurement type. One filter can be configured per measurement quantity.

5. Measurement gaps: Periods that the UE may use to perform measurements,i.e. no (UL, DL) transmissions are scheduled.

The reporting criterion, which is a part of reporting configuration, can either beperiodical or a single event. The following events are specified for reporting:

A1: Serving becomes better than threshold.

A2: Serving becomes worse than threshold.

A3: Neighbour becomes offset better than serving.

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A4: Neighbour becomes better than threshold.

A5: Serving becomes worse than threshold1 and neighbour becomes better thanthreshold2.

B1: Inter RAT neighbour becomes better than threshold.

B2: Serving becomes worse than threshold1 and inter RAT neighbour becomesbetter than threshold2.

An example of measurement configuration is presented in Figure 8.5.

Figure 8.5: Measurement configuration.

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8.2.3 A3 event

To illustrate the event triggered reporting, this section describes details of event A3.Conditions to enter the event, reporting parameters and condition to leave the eventare presented.

Event A3 is the normal event, which is used to trigger intra LTE frequency handoverand this is the reason it was selected as an example. When UE is configured to re-ports measurements upon event A3 takes place, then the UE will sent measurementsif it finds cells, which are several dB (so called offset) stronger than the serving cell.Figure 8.6 illustrates the event together with parameters controlling UE reportingwhen the condition to enter the event is met.

Figure 8.6: Event A3: Neighbour becomes offset better than serving. Frequencyspecific offsets (Ofn andOfs) as well as cell specific offsets (Ocn andOcs) are assumedto be set to zero in this figure.

Condition to enter event A3 (TS 36:331):

Mn+Ofn+Ocn− hysteresis > Ms+Ofs+Ocs+ a3-Offset (8.7)

Condition to leave event A3:

Mn+Ofn+Ocn+ hysteresis < Ms+Ofs+Ocs+ a3-Offset (8.8)

where

Mn – the measurement result of the neighbouring cell, not taking intoaccount any offsets. Expressed in dBm in case of RSRP, or in dBin case of RSRQ

Ofn – the frequency specific offset of the frequency of the neighbour cell(i.e. offsetFreq as defined within measObjectEUTRA correspond-ing to the frequency of the neighbour cell) [dB].

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Ocn – the cell specific offset of the neighbour cell (i.e. cellIndividualOff-set as defined within measObjectEUTRA corresponding to the fre-quency of the neighbour cell), and set to zero if not configured forthe neighbour cell [dB].

Ms – the measurement result of the serving cell, not taking into accountany offsets. Expressed in dBm in case of RSRP, or in dB in caseof RSRQ

Ofs – the frequency specific offset of the serving frequency (i.e. offsetFreqas defined within measObjectEUTRA corresponding to the servingfrequency) [dB].

Ocs – the cell specific offset of the serving cell (i.e. cellIndividualOffsetas defined within measObjectEUTRA corresponding to the servingfrequency), and is set to zero if not configured for the serving cell[dB].

hysteresis – the hysteresis parameter for this event as defined within report-ConfigEUTRA for this event [dB].

a3-Offset – the offset parameter for this event as defined within reportCon-figEUTRA for this event [dB].

s-Measure – defines when the UE is required to perform measurements onneighbouring cells.

riggerQuantity – the quantities used to evaluate the triggering condition for theevent (RSRP or RSRQ).

timeToTrigger – time during which specific criteria for the event needs to be metin order to trigger a measurement report.

ReportInterval – indicates the interval between periodical reports.

reportQuantity – the quantities to be included in the measurement report. Thevalue both means that both the RSRP and RSRQ quantities areto be included in the measurement report.

reportAmount – number of measurement reports sent.

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158

A System information

MIB

dl-Bandwidth, ENUMERATED {n6, n15, n25, n50, n75, n100}phich-Config

phich-Duration, ENUMERATED {normal, extended}phich-Resource, ENUMERATED {oneSixth, half, one, two}

systemFrameNumber, BIT STRING (SIZE (8))

spare, BIT STRING (SIZE (10))

Table A.1: Master Information Block (MIB).

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SIB1

cellAccessRelatedInfo

plmn-IdentityList, SEQUENCE (SIZE (1..6)) OF PLMN-IdentityInfo

PLMN-IdentityInfo

plmn-Identity

mcc, SEQUENCE (SIZE (3)) OF MCC-MNC-Digit

mnc, SEQUENCE (SIZE (2..3)) OF MCC-MNC-Digit

cellReservedForOperatorUse, ENUMERATED {reserved, notReserved}trackingAreaCode, BIT STRING (SIZE (16))

cellIdentity, BIT STRING (SIZE (28)

cellBarred, ENUMERATED barred, notBarred

intraFreqReselection, ENUMERATED allowed, notAllowed

csg-Indication, BOOLEAN

csg-Identity, BIT STRING (SIZE (27))

cellSelectionInfo

q-RxLevMin, INTEGER (-70..-22)

q-RxLevMinOffset, INTEGER (1..8)

p-Max, INTEGER (-30..33)

freqBandIndicator, INTEGER (1..64)

schedulingInfoList

si-Periodicity, ENUMERATED {rf8, rf16, rf32, rf64, rf128, rf256, rf512}sib-MappingInfo, SEQUENCE (SIZE (0..maxSIB-1)) OF SIB-Type

tdd-Config

subframeAssignment, ENUMERATED {sa0, sa1, sa2, sa3, sa4, sa5, sa6}specialSubframePatterns, ENUMERATED {ssp0, ssp1, ssp2, ssp3, ssp4, ssp5,

ssp6, ssp7, ssp8}si-WindowLength, ENUMERATED {ms1, ms2, ms5, ms10, ms15, ms20, ms40}systemInfoValueTag, INTEGER (0..31)

nonCriticalExtension spare bits set to zero

Table A.2: SIB1.

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SIB2

ac-BarringInfo

ac-BarringForEmergency, BOOLEAN

ac-BarringForMO-Signalling, AC-BarringConfig

ac-BarringForMO-Data, AC-BarringConfig

AC-BarringConfig

ac-BarringFactor, ENUMERATED {p00, p05, p10, p15, p20, p25, p30,p40, p50, p60, p70, p75, p80, p85, p90, p95}

ac-BarringTime, ENUMERATED {s4, s8, s16, s32, s64, s128, s256, s512}ac-BarringForSpecialAC, BIT STRING (SIZE(5))

radioResourceConfigCommon

rach-ConfigCommon

preambleInfo

numberOfRA-Preambles, ENUMERATED {n4, n8, n12, n16 ,n20, n24,

n28, n32, n36, n40, n44, n48, n52, n56, n60}preamblesGroupAConfig

powerRampingParameters

powerRampingStep, ENUMERATED {dB0, dB2,dB4, dB6}preambleInitialReceivedTargetPower, ENUMERATED {dBm-120,

dBm-118, dBm-116, dBm-114, dBm-112,dBm-110,

dBm-108, dBm-106, dBm-104, dBm-102, dBm-100,

dBm-98, dBm-96, dBm-94, dBm-92, dBm-90}ra-SupervisionInfo

preambleTransMax, ENUMERATED {n3, n4, n5, n6, n7, n8, n10, n20,n50, n100, n200}

ra-ResponseWindowSize, ENUMERATED {sf2, sf3, sf4, sf5, sf6, sf7,sf8, sf10}

mac-ContentionResolutionTimer, ENUMERATED {sf8, sf16, sf24,sf32, sf40, sf48, sf56, sf64}

maxHARQ-Msg3Tx, INTEGER (1..8)

bcch-Config

pcch-Config

prach-Config

pdsch-ConfigCommon

referenceSignalPower, INTEGER (-60..50)

p-b, INTEGER (0..3)

pusch-ConfigCommon

pusch-ConfigBasic

n-SB, INTEGER (1..4)

hoppingMode, ENUMERATED {interSubFrame,

intraAndInterSubFrame}pusch-HoppingOffset, INTEGER (0..98)

enable64QAM, BOOLEAN

161


ul-ReferenceSignalsPUSCH

pucch-ConfigCommon

soundingRS-UL-ConfigCommon

uplinkPowerControlCommon

p0-NominalPUSCH, INTEGER (-126..24)

alpha, ENUMERATED {al0, al04, al05, al06, al07, al08, al09, al1}p0-NominalPUCCH, INTEGER (-127..-96)

deltaFList-PUCCH

deltaPreambleMsg3, INTEGER (-1..6)

ul-CyclicPrefixLength, ENUMERATED {len1, len2}ue-TimersAndConstants

t300, ENUMERATED {ms100, ms200, ms300, ms400, ms600,

ms1000, ms1500, ms2000}t301, ENUMERATED {ms100, ms200, ms300, ms400, ms600,

ms1000, ms1500, ms2000}t310, ENUMERATED {ms0, ms50, ms100, ms200, ms500, ms1000, ms2000}n310, ENUMERATED {n1, n2, n3, n4, n6, n8, n10, n20}t311, ENUMERATED {ms1000, ms3000, ms5000, ms10000,

ms15000, ms20000, ms30000}n311, ENUMERATED {n1, n2, n3, n4, n5, n6, n8, n10}

freqInfo

ul-CarrierFreq, ARFCN-ValueEUTRA

ul-Bandwidth, ENUMERATED {n6, n15, n25, n50, n75, n100}additionalSpectrumEmission, INTEGER (1..32)

mbsfn-SubframeConfigList

timeAlignmentTimerCommon, ENUMERATED {sf500, sf750, sf1280, sf1920,sf2560, sf5120, sf10240, infinity}

Table A.3: SIB2.

162

SIB3

cellReselectionInfoCommon

q-Hyst, ENUMERATED {B0, dB1, dB2, dB3, dB4, dB5, dB6, dB8, dB10,dB12, dB14, dB16, dB18, dB20, dB22, dB24}

speedStateReselectionPars

mobilityStateParameters

t-Evaluation, ENUMERATED {s30, s60, s120, s180, s240,spare3, spare2, spare1}

t-HystNormal, ENUMERATED {s30, s60, s120, s180, s240,spare3, spare2, spare1}

n-CellChangeMedium, INTEGER (1..16)

n-CellChangeHigh, INTEGER (1..16)

q-HystSF

sf-Medium, ENUMERATED {dB-6, dB-4, dB-2, dB0}sf-High, ENUMERATED {dB-6, dB-4, dB-2, dB0}

cellReselectionServingFreqInfo

s-NonIntraSearch, INTEGER (0..31)

ThreshServingLow, INTEGER (0..31)

cellReselectionPriority, INTEGER (0..7)

intraFreqCellReselectionInfo



s-IntraSearch, INTEGER (0..31)

allowedMeasBandwidth, ENUMERATED {mbw6, mbw15, mbw25, mbw50,

mbw75, mbw100}presenceAntennaPort1, BOOLEAN

neighCellConfig, BIT STRING (SIZE (2))

t-ReselectionEUTRA, INTEGER (0..7)

t-ReselectionEUTRA-SF

sf-Medium, ENUMERATED {oDot25, oDot5, oDot75, lDot0}sf-High, ENUMERATED {oDot25, oDot5, oDot75, lDot0}

Table A.4: SIB3.

163


SIB4

intraFreqNeighCellList, SEQUENCE (SIZE (1..maxCellIntra)) OF

IntraFreqNeighCellInfo

intraFreqBlackCellList, SEQUENCE (SIZE (1..maxCellBlack)) OF

PhysCellIdRange

csg-PhysCellIdRange, PhysCellIdRange

IntraFreqNeighCellInfo

physCellId, INTEGER (0..503)

q-OffsetCell, ENUMERATED {dB-24, dB-22, dB-20, dB-18, dB-16, dB-14,dB-12, dB-10, dB-8, dB-6, dB-5, dB-4, dB-3, dB-2, dB-1,

dB0, dB1, dB2, dB3, dB4, dB5, dB6, dB8, dB10, dB12

dB14, dB16, dB18, dB20, dB22, dB24}PhysCellIdRange

start, INTEGER (0..503)

range, ENUMERATED {n4, n8, n12, n16, n24, n32, n48, n64, n84, n96,n128, n168, n252, n504, spare2, spare1}

Table A.5: SIB4.

164

SIB5

interFreqCarrierFreqList, SEQUENCE (SIZE (1..maxFreq)) OF

InterFreqCarrierFreqInfo

InterFreqCarrierFreqInfo

dl-CarrierFreq, INTEGER (0..maxEARFCN)



t-ReselectionEUTRA, INTEGER (0..7)

t-ReselectionEUTRA-SF

sf-Medium, ENUMERATED {oDot25, oDot5, oDot75, lDot0}sf-High, ENUMERATED {oDot25, oDot5, oDot75, lDot0}

threshX-High, INTEGER (0..31)

threshX-Low, INTEGER (0..31)

allowedMeasBandwidth, ENUMERATED {mbw6, mbw15, mbw25, mbw50,

mbw75, mbw100}presenceAntennaPort1, BOOLEAN

cellReselectionPriority, INTEGER (0..7)

neighCellConfig, BIT STRING (SIZE (2))

q-OffsetFreq, dB-24, dB-22, dB-20, dB-18, dB-16, dB-14, dB-12, dB-10,

dB-8, dB-6, dB-5, dB-4, dB-3, dB-2, dB-1, dB0, dB1, dB2, dB3, dB4,

dB5, dB6, dB8, dB10, dB12, dB14, dB16, dB18, dB20, dB22, dB24}interFreqNeighCellList, InterFreqNeighCellList

interFreqBlackCellList, SEQUENCE (SIZE (1..maxCellBlack)) OF

PhysCellIdRange

InterFreqNeighCellInfo

physCellId, INTEGER (0..503)

q-OffsetCell, dB-24, dB-22, dB-20, dB-18, dB-16, dB-14, dB-12, dB-10,

dB-8, dB-6, dB-5, dB-4, dB-3, dB-2, dB-1, dB0, dB1, dB2, dB3, dB4,

dB5, dB6, dB8, dB10, dB12, dB14, dB16, dB18, dB20, dB22, dB24}

Table A.6: SIB5.

165


166

List of Figures

1.1 Two way communication. . . . . . . . . . . . . . . . . . . . . . . . . 5

1.2 Frequency Division Duplex (FDD) and Time Division Duplex (TDD). 5

1.3 Multiple access. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.4 Cellular technologies evolution. . . . . . . . . . . . . . . . . . . . . . 7

1.5 Frequency Division Multiple Access (FDMA). . . . . . . . . . . . . 8

1.6 Time Division Multiple Access (TDMA). . . . . . . . . . . . . . . . 8

1.7 Code Division Multiple Access (CDMA). . . . . . . . . . . . . . . . 9

1.8 Orthogonal Frequency Division Multiple Access (OFDMA). . . . . . 10

1.9 OFDM subcarriers. . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1.10 Geometric representation of a complex number in the rectangularnotation in a complex Cartesian plane. . . . . . . . . . . . . . . . . 13

1.11 Conjugate z∗ of a complex number z. . . . . . . . . . . . . . . . . . 13

1.12 Geometric representation of a complex number in the polar notation. 14

1.13 Euler’s formula. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

1.14 Fourier Transform (FT) principles. . . . . . . . . . . . . . . . . . . . 16

1.15 Example of the Discrete Fourier Transform (DFT). . . . . . . . . . 17

1.16 The coefficient wn in the DFT for N = 8. . . . . . . . . . . . . . . . 18

1.17 The coefficient w−n in the IDFT for N = 8. When comparing withFigure 1.16 notice that w−n is a conjugate of wn. . . . . . . . . . . 20

1.18 Graphical presentation of the IDFT example. . . . . . . . . . . . . . 21

1.19 OFDM concept. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

1.20 OFDM transmitter. . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

1.21 OFDM receiver. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

1.22 LTE modulations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

2.1 EPS architecture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

2.2 EPS bearer concept. . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

2.3 E-UTRAN, UTRAN and GERAN architecture. GPRS one tunnelapproach. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

2.4 Typical implementation of LTE/SAE. Combined SGSN/MME onetunnel approach. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

2.5 Inter-pool mobility. . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

3.1 User plane for LTE. . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

3.2 Control plane for LTE. . . . . . . . . . . . . . . . . . . . . . . . . . 50

3.3 Relation between NAS and AS. . . . . . . . . . . . . . . . . . . . . 52

3.4 HARQ principle - four multiple HARQ processes. . . . . . . . . . . 54

3.5 LTE radio interface structure for DL. . . . . . . . . . . . . . . . . . 56

4.1 LTE channels mapping. . . . . . . . . . . . . . . . . . . . . . . . . . 60

4.2 LTE FDD time domain structure. . . . . . . . . . . . . . . . . . . . 62

167

LIST OF FIGURES

4.3 Cyclic prefix concept. . . . . . . . . . . . . . . . . . . . . . . . . . . 62

4.4 LTE TDD frame structure for UL-DL configuration 2. . . . . . . . 62

4.5 Special subframe configuration. . . . . . . . . . . . . . . . . . . . . . 64

4.6 LTE downlink physical resource. . . . . . . . . . . . . . . . . . . . 65

4.7 Definition of channel bandwidth and transmission bandwidth config-uration for one E-UTRAN carrier. . . . . . . . . . . . . . . . . . . . 66

4.8 An example of DL resource allocation. . . . . . . . . . . . . . . . . 66

4.9 Localized and distributed VRB. The picture illustrates Ngap,1 = 48for NRB

DL = 100. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

5.1 Primary/secondary synchronization signal and PBCH structure forFDD (normal cyclic prefix). . . . . . . . . . . . . . . . . . . . . . . . 71

5.2 Primary/secondary synchronization signal and PBCH structure forTDD (normal cyclic prefix). . . . . . . . . . . . . . . . . . . . . . . 72

5.3 Zadoff-Chu sequence transmitted on 31 lower frequency band sub-carriers for physicalLayerId = 0, which corresponds to root indexu = 25. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

5.4 Mapping of Physical Channels on DL for FDD mode. Time on hor-izontal axis and frequency on vertical axis. . . . . . . . . . . . . . . 74

5.5 Downlink reference signal structure in a cell supporting non-MBSFNtransmission with normal cyclic prefix and CellID = 0. . . . . . . . 76

5.6 Cell specific RS frequency shift. . . . . . . . . . . . . . . . . . . . . 77

5.7 System information. . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

5.8 Control Channel Element (CCE). . . . . . . . . . . . . . . . . . . . 82

5.9 Physical layer PDCCH processing. . . . . . . . . . . . . . . . . . . . 82

5.10 PDCH blind decoding example. . . . . . . . . . . . . . . . . . . . . 85

5.11 PDCH blind decoding. . . . . . . . . . . . . . . . . . . . . . . . . . 85

5.12 Transport channel processing for DL-SCH, PCH and MCH. . . . . . 86

5.13 Physical layer PDSCH processing. . . . . . . . . . . . . . . . . . . . 87

5.14 CRC concept. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

5.15 Rate 1/3 tail biting convolutional encoder. . . . . . . . . . . . . . . 89

5.16 Structure of rate 1/3 turbo encoder (dotted lines apply for trellistermination only). The initial value of the shift registers of the 8-state constituent encoders is all zeros when starting to encode theinput bits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

5.17 Interleaver. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

5.18 Operations of circular buffer rate matching for turbo code. . . . . . 91

5.19 Codeword-to-layer mapping for spatial multiplexing and transmitdiversity. The picture also presents the precoding for transmit di-versity. The size of the codeword(s) correspond to the maximumthroughput possible to achieve for particular layer mapping. It can beobserved that in spatial multiplexing maximum throughput increaseswith the the number of layers. In transmit diversity, regardless ofthe number of antennas, the maximum throughput is not increased. 93

5.20 Spatial multiplexing with one layer and two antenna ports. . . . . . 96

5.21 PHICH. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

6.1 SC-FDMA versus OFDMA spectral power distribution. . . . . . . 101

6.2 Block diagram of the UL DFT-s-OFDM transmitter. . . . . . . . . 102

6.3 UL resource allocation. . . . . . . . . . . . . . . . . . . . . . . . . . 103

168

LIST OF FIGURES

6.4 UL subframe structure for normal cyclic prefix. . . . . . . . . . . . . 1036.5 UL frequency hopping. . . . . . . . . . . . . . . . . . . . . . . . . . 1046.6 UL RS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1046.7 UL SRS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1066.8 PUCCH resources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1066.9 PUCCH format 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1076.10 PUCCH format 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1086.11 Preamble formats. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1106.12 Time-frequency structure of non-synchronised RA for FDD. Exam-

ple for prach-ConfigIndex = 6 and prach-FreqOffset = 1. . . . . . . . 111

7.1 Uplink-downlink timing relation from UE perspective for FDD. . . . 1147.2 Uplink-downlink time relation from UE perspective for TDD. . . . . 1147.3 Random access timing advance. . . . . . . . . . . . . . . . . . . . . 1157.4 Adjustment of timing advance by MAC control element. . . . . . . . 1167.5 UE time synchronisation. . . . . . . . . . . . . . . . . . . . . . . . . 1177.6 RA process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1187.7 DL resource allocation. . . . . . . . . . . . . . . . . . . . . . . . . . 1187.8 Multi antenna possibilities. . . . . . . . . . . . . . . . . . . . . . . 1217.9 SU-MIMO and MU-MIMO. . . . . . . . . . . . . . . . . . . . . . . . 1217.10 Spatial multiplexing principles. . . . . . . . . . . . . . . . . . . . . 1227.11 Transmit diversity . . . . . . . . . . . . . . . . . . . . . . . . . . . 1237.12 Transmission mode 3: spatial multiplexing with large delay CDD or

transmit diversity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1247.13 MIMO antenna solutions. . . . . . . . . . . . . . . . . . . . . . . . 1247.14 UE reporting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1267.15 Open loop power control. . . . . . . . . . . . . . . . . . . . . . . . . 1347.16 Closed loop power control. . . . . . . . . . . . . . . . . . . . . . . . 1347.17 Accumulated method of the closed loop power control adjustment. . 1377.18 Absolute method of the closed loop power control adjustment. . . . 1377.19 Transmitted power and signal at eNB as a function of the RSRP for

the following parameters setting: PCMAX = 23 dBm, MPUSCH = 1,P0 PUSCH = −109 dBm, α = 1, referenceSignalPower = 15 dBm. . 138

7.20 The target PSDRX and the TBS. . . . . . . . . . . . . . . . . . . . 139

8.1 Overall idle mode process. . . . . . . . . . . . . . . . . . . . . . . . 1428.2 Automatic PLMN selection process. . . . . . . . . . . . . . . . . . . 1458.3 Cell reselection criterion. . . . . . . . . . . . . . . . . . . . . . . . . 1488.4 X2 handover. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1498.5 Measurement configuration. . . . . . . . . . . . . . . . . . . . . . . . 1538.6 Event A3: Neighbour becomes offset better than serving. Frequency

specific offsets (Ofn and Ofs) as well as cell specific offsets (Ocn andOcs) are assumed to be set to zero in this figure. . . . . . . . . . . . 154

169

LIST OF FIGURES

170

List of Tables

2.1 QoS Class Identifier (QCI) defined for LTE/SAE. . . . . . . . . . . 35

2.2 Mapping between standardized QCIs and pre-Relese-8 QoS parame-ter values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

4.1 Cyclic prefix types. . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

4.2 Uplink-downlink configuration for LTE TDD. ↓ denotes a subframereserved for downlink transmission. ↑ denotes a subframe reservedfor uplink transmission. S denotes a special subframe. . . . . . . . . 63

4.3 Special subframe configuration. . . . . . . . . . . . . . . . . . . . . . 64

4.4 Number of RBs for different channel bandwidths in FDD and TDD. 65

4.5 RB gap values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

4.6 GSM, UMTS, WiMAX and LTE comparison. The table presentsgross bit rate, spectral efficiency and system spectral efficiency, whichinclude not only user date bit rate but also system signalling. Thetable does not consider MIMO which can further increase spectralefficiency. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

5.1 S-SS sequence generation. . . . . . . . . . . . . . . . . . . . . . . . . 73

5.2 Number of OFDM symbols used for PDCCH. The NDLRB is the down-

link bandwidth configuration, expressed in number of RB, see Table4.4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

5.3 Supported PDCCH formats. . . . . . . . . . . . . . . . . . . . . . . 81

5.4 Usage of channel coding scheme and coding rate for control information. 89

5.5 Codeword-to-layer mapping for spatial multiplexing. . . . . . . . . . 94

5.6 Codeword-to-layer mapping for transmit diversity.∗In case when M

(0)symb mod 4 ̸= 0 then two null symbols are appended

to d(0)(M(0)symb − 1). . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

5.7 Codebook for transmission on antenna ports {0, 1}. . . . . . . . . . 96

5.8 DL physical channels modulation. . . . . . . . . . . . . . . . . . . . 100

6.1 Random access preamble parameters. . . . . . . . . . . . . . . . . . 109

7.1 Type 0 resource allocation RBG size vs. downlink system bandwidth. 119

7.2 PDSCH transmission scheme. . . . . . . . . . . . . . . . . . . . . . . 125

7.3 Physical Channels for Aperiodic or Periodic CQI reporting. . . . . . 127

7.4 4-bit CQI Table. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

7.5 CQI and PMI Feedback Types for PUSCH reporting modes. . . . . 128

7.6 PUSCH reporting modes for different transmission modes. . . . . . 129

7.7 Subband size (k) vs. System Bandwidth. . . . . . . . . . . . . . . . 129

7.8 CQI and PMI Feedback Types for PUCCH reporting modes. . . . . 130

7.9 PUCCH reporting modes for different transmission modes. . . . . . 130

171

LIST OF TABLES

7.10 Modulation and TBS index table for PDSCH. . . . . . . . . . . . . 1327.11 Transport block size table. . . . . . . . . . . . . . . . . . . . . . . . 1337.12 Mapping of TPC Command Field in DCI format 0/3 to absolute and

accumulated δPUSCH values. . . . . . . . . . . . . . . . . . . . . . . 1367.13 Mapping of TPC Command Field in DCI format 3A to accumulated

δPUSCH values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1367.14 P0 PUSCH calculation. . . . . . . . . . . . . . . . . . . . . . . . . . . 1407.15 referenceSignalPower calculation. . . . . . . . . . . . . . . . . . . 140

A.1 Master Information Block (MIB). . . . . . . . . . . . . . . . . . . . 157A.2 SIB1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158A.3 SIB2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160A.4 SIB3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161A.5 SIB4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162A.6 SIB5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

172

Acronyms

1G 1st Generation

16QAM 16 Quadrature Amplitude Modulation

1xRTT 1x Radio Transmission Technology

2G 2nd Generation

3G 3rd Generation

3GPP 3rd Generation Partnership Project

3GPP TS 3GPP Technical Specification

4G 4th Generation

64QAM 64 Quadrature Amplitude Modulation

AAA Authentication, authorisation and accounting

ACK Acknowledge

A/D Analogue-to-Digital converter

AM Acknowledged Mode

AMPS Advanced Mobile Phone Systems

ARQ Automatic Repeat reQuest

AS Access Stratum

AS Application Server

BCCH Broadcast Control Channel

BCH Broadcast Channel

BLER Block Error Rate

BPSK Binary Phase Shift Keying

BS Base Station

BSS Base Station System

C Carrier

CAZAC Constant Amplitude Zero AutoCorrelation

CCCH Common Control Channel

173

ACRONYMS

CCE Control Channel Element

DCI Downlink Control Information

CDD Cyclic Delay Diversity

CDMA Code Division Multiple Access

CDMA2000 Code Division Multiple Access 2000

CM Connection Management

CN Core Network

CP Control Plane

CQI Channel Quality Indicator

CRC Cyclic Redundancy Check

C-RNTI Cell RNTI

CS Circuit Switched

D/A Digital-to-Analogue converter

DAB Digital Audio Broadcasting

D-AMPS Digital Advanced Mobile Phone Systems

DCCH Dedicated Control Channel

DFT Discrete Fourier Transform

DFT-s-OFDM Discrete Fourier Transform spread-OFDM

DL Downlink

DL-SCH Downlink Shared Channel

DRX Discontinuous Reception

DTCH Dedicated Traffic Channel

DwPTS Downlink Pilot Time Slot

DVB-T Digital Video Broadcasting – Terrestrial

ECM EPS Connection Management

EDGE Enhanced Data rates for GSM Evolution

EGPRS Enhanced GPRS

EHPLMN Equivalent HPLMN

EIR Equipment Identify Register

EMM EPS Mobility Management

eNB Evolved Node B

EPC Evolved Packet Core

EPS Evolved Packet System

174

E-RAB E-UTRAN Radio Access Bearer

ETWS Earthquake and Tsunami Warning System

E-UTRA Evolved Universal Terrestrial Radio Access

E-UTRAN Evolved UMTS Terrestrial Radio Access Network

FDD Frequency Division Duplex

FDMA Frequency Division Multiple Access

FFT Fast Fourier Transform

FT Fourier Transform

GBR Guaranteed Bit Rate

GERAN GSM EDGE Radio Access Network

GGSN Gateway GPRS Support Node

GP Guard Period

GPRS General Packet Radio Service

GMM GPRS Mobility Management

GSM Global System for Mobile communication

GTP GPRS Tunnelling Protocol

GTP-C GTP Control plane

GTP-U GTP User data tunnelling

HARQ Hybrid Automatic Repeat reQuest

HO Handover

HPLMN Home PLMN

HRPD High Rate Packet Data

HSDPA High Speed Downlink Packet Access

HSPA High Speed Packet Access

HSS Home Subscriber Server

I Interferer

ICI Inter Carrier Interference

IDFT Inverse Discrete Fourier Transform

IETF Internet Engineering Task Force

IFFT Inverse Fast Fourier Transform

IMS IP Multimedia Subsystem

IMSI International Mobile Subscriber Identity

IP Internet Protocol

175

ACRONYMS

Inter-RAT Inter Radio Access Technology

ISI Inter Symbol Interference

ITU International Telecommunication Union

IWLAN Interworking Wireless Local Area Network

L1 Layer 1

L2 Layer 2

LA Link Adaptation

LTE Long Term Evolution

LTE/SAE Long Term Evolution/System Architecture Evolution

MAC Medium Access Control

MBMS Multimedia Broadcast and Multicast Services

MBSFN Multicast Broadcast Single Frequency Network

MCCH Multicast Control Channel

MCH Multicast Channel

MCS Modulation and Coding Scheme

MIB Master Information Block

MIMO Multiple Input Multiple Output

MM Mobility Management

MME Mobility Management Entity

MMS Multimedia Messaging Services

MTCH Multicast Traffic Channel

MU-MIMO Multi User MIMO

N Noise

NACK Negative Acknowledge

NAS Non-Access Stratum

NMT Nordic Mobile Telephony

OFDM Orthogonal Frequency Division Multiplexing

OFDMA Orthogonal Frequency Division Multiple Access

PAPR Peak-to-Average Power Ratio

PBCH Physical Broadcast Channel

PCCH Paging Control Channel

PCEF Policy and Charging Enforcement Function

PCFICH Physical Control Format Indicator Channel

176

PCH Paging Channel

PCRF Policy and Charging Rules Function

PDCCH Physical Downlink Control Channel

PDCP Packet Data Convergence Protocol

PDP Packet Data Protocol

PDSCH Physical Downlink Shared Channel

PDU Packet Data Unit

P-GW Packet Data Network Gateway

PHICH Physical Hybrid ARQ Indicator Channel

PLMN Public Land Mobile Network

PMCH Physical Multicast Channel

PMI Precoding Matrix Indicator

PMIP Proxy Mobile IP

PoP Point of Presence

PRACH Physical Random Access Channel

PRB Physical Resource Block

PS Packet Switched

P/S-GW Packet Data Network/Serving Gateway

PSK Phase Shift Keying

P-SS Primary Synchronisation Signals

PUCCH Physical Uplink Control Channel

PUSCH Physical Uplink Shared Channel

QAM Quadrature Amplitude Modulation

QCI QoS Class Identifier

QoS Quality of Service

QPSK Quadrature Phase Shift Keying

RA Random Access

RACH Random Access Channel

RAN Radio Access Network

RANAP RAN Application Part

RA-RNTI Random Access Radio Network Temporary Identity

RAT Radio Access Technology

RB Resource Block

177

ACRONYMS

RE Resource Element

REG Resource Element Group

RF Radio Frequency

RI Rank Indicator

RLC Radio Link Control

RLF Radio Link Failure

RNC Radio Network Controller

RNL Radio Network Layer

RNTI Radio Network Temporary Identity

ROHC Robust Header Compression

RRC Radio Resource Control

RRM Radio Resource Management

RS Reference Signals

RSRP Reference Signal Received Power

RSRQ Reference Signal Received Quality

S1AP S1 Application Protocol

SAE System Architecture Evolution

SAE-GW System Architecture Evolution Gateway

SB Scheduling Block

SC-FDMA Single Carrier Frequency Division Multiple Access

SCTP Stream Control Transmission Protocol

SDF Service Data Flow

SDU Service Data Unit

SGSN Serving GPRS Support Node

S-GW Serving Gateway

SI System Information

SIB System Information Block

SINR Signal to Interference and Noise Ratio

SI-RNTI System Information RNTI

SM Session Management

SMS Short Message Service

SN Sequence Number

SRB Signalling Radio Bearer

178

SRS Sounding Reference Signal

S-SS Secondary Synchronisation Signals

SU-MIMO Single User MIMO

TA Tracking Area

TAU Tracking Area Update

TBS Transport Blok Size

TCP Transmission Control Protocol

TDD Time Division Duplex

TDMA Time Division Multiple Access

TFT Traffic Flow Template

TNL Transport Network Layer

TPC Transmit Power Control

TS Time Slot

TTI Transmission Time Interval

TX Transmit

UE User Equipment

UL Uplink

UM Unacknowledged Mode

UMTS Universal Mobile Telecommunications System

UP User Plane

UpPTS Uplink Pilot Time Slot

UL-SCH Uplink Shared Channel

USIM Universal Subscriber Identity Module

UTRAN Universal Terrestrial Radio Access Network

VoIP Voice over IP

VPLMN Visited PLMN

VRB Virtual Resource Block

WCDMA Wideband Code Division Multiple Access

WiMAX Worldwide Interoperability for Microwave Access

WLAN Wireless Local Area Network

X2AP X2 Application Protocol

179

ACRONYMS

180

elp 4003 lte air interface

Documents

lte requirements

lte downlink physical

g ofdma

enki adam girycki

lte general principles452

lte air interfaceesb

training document

pdcch processing