Download - 02 Ra41202en20gla0 Lte Air Interface v03
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LTE RPESSLTE Air Interface
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Nokia Siemens Networks Academy
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Module Objectives
After completing this module, the participant should be able to:
Understand the basics of the OFDM transmission technology Explain how the OFDM technology avoids the Inter Symbol Interference Recognise the different between OFDM & OFDMA Identify the OFDM weaknesses Review the key OFDM parameters Analyze the reasons for SC-FDMA selection in UL Describe the LTE Air Interface Physical Layer Calculate the Physical Layer overhead Identify LTE Measurements List the frequency allocation alternatives for LTE Review the main LTE RRM features Identify the main voice solutions for LTE
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Module Contents
OFDM Basics OFDM & Multipath Propagation: The Cyclic Prefix OFDM versus OFDMA OFDM Weaknesses OFDM Key Parameters SC-FDMA LTE Air Interface Physical Layer Physical Layer Overhead LTE Measurements Frequency Variants RRM Overview VoIP in LTE
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Module Contents
OFDM Basics OFDM & Multipath Propagation: The Cyclic Prefix OFDM versus OFDMA OFDM Weaknesses OFDM Key Parameters SC-FDMA LTE Air Interface Physical Layer Physical Layer Overhead LTE Measurements Frequency Variants RRM Overview VoIP in LTE
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The Rectangular Pulse
Advantages:+ Simple to implement: there is no complex filter system required to detect such pulses and to generate them.+ The pulse has a clearly defined duration. This is a major advantage in case of multi-path propagation environments as it simplifies handling of inter-symbol interference.
Disadvantage: - it allocates a quite huge spectrum. However the spectral power density has null points exactly at multiples of the frequency fs = 1/Ts. This will be important in OFDM.
time
ampl
itude
Ts f s =1Ts
Time Domain
frequency f/fs
spec
tral
pow
er d
ensi
ty Frequency Domain
fs
FourierTransform
Inverse FourierTransform
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TDMA
f
t
f
Time Division
FDMA
f
f
t
Frequency Division
CDMA
f
tcode
s
f
Code Division
OFDMA
f
f
t
Frequency Division Orthogonal subcarriers
Multiple Access Methods User 1 User 2 User 3 User ..
OFDM is the state-of-the-art and most efficient and robust air interface
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OFDM Basics
Transmits hundreds or even thousands of separately modulated radio signals using orthogonal subcarriers spread across a wideband channel
Orthogonality:
The peak ( centre frequency) of one subcarrier
intercepts the nulls of the neighbouring subcarriers
15 kHz in LTE: fixed
Total transmission bandwidth
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OFDM Basics
Data is sent in parallel across the set of subcarriers, each subcarrier only transports a part of the whole transmission
The throughput is the sum of the data rates of each individual (or used) subcarriers while the power is distributed to all used subcarriers
FFT ( Fast Fourier Transform) is used to create the orthogonal subcarriers. The number of subcarriers is determined by the FFT size ( by the bandwidth)
Power
frequency
bandwidth
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Module Contents
OFDM Basics OFDM & Multipath Propagation: The Cyclic Prefix OFDM versus OFDMA OFDM Weaknesses OFDM Key Parameters SC-FDMA LTE Air Interface Physical Layer Physical Layer Overhead LTE Measurements Frequency Variants RRM Overview VoIP in LTE
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Tg: Guard period durationISI: Inter-Symbol Interference
Propagation delay exceeding the Guard Period
12
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time
TSYMBOLTime Domain
time
time
Tg
1
2
3
time
4
Delay spread > Tg ISI
The Guard Period should be designed such that it is always longer than the multipath delay spread, in order to avoid inter-symbol interference between successive OFDM symbols.Note that in the example of this slide, the Guard Period is too short, so there will be inter-symbol interference!
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The Cyclic Prefix OFDM symbol
OFDM symbol
OFDM symbol
OFDM symbol
Cyclic prefix
Part of symbol used for FFT processing in the receiver
In all major implementations of the OFDMA technology (LTE, WiMAX) the Guard Periodis equivalent to the Cyclic Prefix CP.
This technique consists in copying the last part of a symbol shape for a duration of guard-time and attaching it in front of the symbol (refer to picture sequence on the right).
CP needs to be longer than the channel multipath delay spread (refer to previous slide).
A receiver typically uses the high correlation between the CP and the last part of the following symbol to locate the start of the symbol and begin then with decoding.
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The OFDM Signal
The OFDM signal is made of multiple subcarriers.The distance between the center frequencies of the subcarriers is exactly the inverse of the Symbol period (Ts). Bigger Ts means subcarriers will allocated closer and more subcarriers could be allocated on a given spectrum bandwidth.An OFDM symbol is the combination of n subcarrier Symbol being produced in parallel at the same time.
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Module Contents
OFDM Basics OFDM & Multipath Propagation: The Cyclic Prefix OFDM versus OFDMA OFDM Weaknesses OFDM Key Parameters SC-FDMA LTE Air Interface Physical Layer Physical Layer Overhead LTE Measurements Frequency Variants RRM Overview VoIP in LTE
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OFDM
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Plain OFDM
time
subc
arrie
r
...
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...
...
...
...
...
...
1 2 3 common info(may be addressed viaHigher Layers)
UE 1 UE 2 UE 3
OFDM stands for Orthogonal Frequency Division Multicarrier
OFDM: Plain or Normal OFDM has no built-in multiple-access mechanism.
This is suitable for broadcast systems like DVB-T/H which transmit only broadcast and multicast signals and do not really need an uplink feedback channel (although such systems exist too).
Now we have to analyze how to handle access of multiple users simultaneously to the system, each one using OFDM.
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OFDMA
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1
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Orthogonal FrequencyMultiple Access
OFDMAtime
...
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...
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...
...
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11
1 1
222
2 2
3 33 3 3
1
subc
arrie
r
11 1 1
111
3 3 333 3 3 33
Resource Block (RB)
1 2 3 common info(may be addressed viaHigher Layers)
UE 1 UE 2 UE 3
OFDMA stands for Orthogonal Frequency Division Multiple Access
registered trademark by Runcom Ltd. The basic idea is to assign subcarriers to users based on their
bit rate services. With this approach it is quite easy to handlehigh and low bit rate users simultaneously in a single system.
But still it is difficult to run highly variable traffic efficiently. The solution to this problem is to assign to a single users so
called resource blocks or scheduling blocks. such block is simply a set of some subcarriers over some
time. A single user can then use 1 or more Resource Blocks.
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Module Contents
OFDM Basics OFDM & Multipath Propagation: The Cyclic Prefix OFDM versus OFDMA OFDM Weaknesses OFDM Key Parameters SC-FDMA LTE Air Interface Physical Layer Physical Layer Overhead LTE Measurements Frequency Variants RRM Overview VoIP in LTE
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Inter-Carrier Interference (ICI) in OFDM
The price for the optimum subcarrier spacing is the sensitivity of OFDM to frequency errors. If the receivers frequency slips some fractions from the subcarriers center frequencies,
then we encounter not only interference between adjacent carriers, but in principle between all carriers.
This is known as Inter-Carrier Interference (ICI) and sometimes also referred to as Leakage Effect in the theory of discrete Fourier transform.
One possible cause that introduces frequency errors is a fast moving Transmitter or Receiver (Doppler effect).
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f0 f1 f2 f3 f4
P
I3I1I4I0
ICI =
Inte
r-C
arrie
r Int
erfe
renc
e
Leakage effect due to Frequency Drift: ICI
Two effects begin to work:1. -Subcarrier 2 has no longer its
power density maximum here -so we loose some signal energy.
2.-The rest of subcarriers (0, 1, 3 and 4) have no longer a null point here. So we get some noise from the other subcarrier.
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Module Contents
OFDM Basics OFDM & Multipath Propagation: The Cyclic Prefix OFDM versus OFDMA OFDM Weaknesses OFDM Key Parameters SC-FDMA LTE Air Interface Physical Layer Physical Layer Overhead LTE Measurements Frequency Variants RRM Overview VoIP in LTE
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OFDMA Parameters in LTE
Channel bandwidth: DL bandwidths ranging from 1.4 MHz to 20 MHz Data subcarriers: the number of data subcarriers varies with the
bandwidth 72 for 1.4 MHz to 1200 for 20 MHz
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OFDMA Parameters in LTE Frame duration: 10ms created from slots and subframes. Subframe duration (TTI): 1 ms ( composed of two 0.5ms slots) Subcarrier spacing: Fixed to 15kHz ( 7.5 kHz defined for MBMS) Sampling Rate: Varies with the bandwidth but always factor or
multiple of 3.84 to ensure compatibility with WCDMA by using common clocking
Frame Duration
Subcarrier Spacing
Sampling Rate ( MHz)
Data Subcarriers
Symbols/slot
CP length
1.4MHz 3 MHz 5 MHz 10 MHz 15 MHz 20 MHz
10 ms
15 kHz
Normal CP=7, extended CP=6
Normal CP=4.69/5.12 s, extended CP= 16.67s.
1.92 3.84 7.68 15.36 23.04 30.72
72 180 300 600 900 1200
10ms
Fixed 15kHz: reduces the complexity of a system supporting multiple channel bandwidthsMBMS: Multimedia Broadcast Multicast system
To ensure that all signals are received correctly, the receiver sampling rate must be slightly higher than the bandwidth of the signal used to carry it (i.e. for a channel bandwidth of 1.75MHz the sampling rate should be 2 MHz)
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Module Contents
OFDM Basics OFDM & Multipath Propagation: The Cyclic Prefix OFDM versus OFDMA OFDM Weaknesses OFDM Key Parameters SC-FDMA LTE Air Interface Physical Layer Physical Layer Overhead LTE Measurements Frequency Variants RRM Overview VoIP in LTE
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Peak-to-Average Power Ratio in OFDMA
The transmitted power is the sum of the powers of all the subcarriers
Due to large number of subcarriers, the peak to average power ratio (PAPR) tends to have a large range
The higher the peaks, the greater the range of power levels over which the transmitter is required to work.
Not best suited for use with mobile (battery-powered) devices
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SC-FDMA in UL
Single Carrier Frequency Division Multiple Access: Transmission technique used for Uplink
Variant of OFDM that reduces the PAPR: Combines the PAR of single-carrier system with the
multipath resistance and flexible subcarrier frequency allocation offered by OFDM.
It can reduce the PAPR between 69dB compared to OFDMA
TS36.201 and TS36.211 provide the mathematical description of the time domain representation of an SC-FDMA symbol.
Reduced PAPR means lower RF hardware requirements (power amplifier)
SC-FD
MA
OFD
MA
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SC-FDMA and OFDMA Comparison (2/2)
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Module Contents
OFDM Basics OFDM & Multipath Propagation: The Cyclic Prefix OFDM versus OFDMA OFDM Weaknesses OFDM Key Parameters SC-FDMA LTE Air Interface Physical Layer Physical Layer Overhead LTE Measurements Frequency Variants RRM Overview VoIP in LTE
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LTE Physical Layer - Introduction
FDD..
..
..
..
Downlink Uplink
Frequency band 1
Frequency band 2
.. ..Single frequency bandTDD
It provides the basic bit transmission functionality over air LTE physical layer based on OFDMA DL & SC-FDMA in UL
This is the same for both FDD & TDD mode of operation There is no macro-diversity in use System is reuse 1, single frequency network operation is feasible
no frequency planning required There are no dedicated physical channels anymore, as all resource
mapping is dynamically driven by the scheduler
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LTE Physical Layer Structure Frame Structure (FDD)
10 ms frame
0.5 ms slot
s0 s1 s2 s3 s4 s5 s6 s7 s18 s19..
1 ms sub-frame
SF0 SF1 SF2 SF9..
sy4sy0 sy1 sy2 sy3 sy5 sy6
0.5 ms slot
SF3
SF: SubFrame
s: slot
Sy: symbol
FDD Frame structure ( also called Type 1 Frame) is common to both UL & DL Divided into 20 x 0.5ms slots
Structure has been designed to facilitate short round trip time
- Frame length = 10 ms- FDD: 10 sub-frames of 1 ms for UL & DL- 1 Frame = 20 slots of 0.5ms each- 1 slot = 7 (normal CP) or 6 OFDM
symbols (extended CP)
In FDD, there is a time offset between uplink and downlink transmission.
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LTE Physical Layer Structure Frame Structure (TDD)
SF#0SF#0
. . .f
time
UL/DL carrier
radio frame 10 ms
subframe
Dw
PTS
Dw
PTS
GPGP
UpP
TSU
pPTS SF
#2SF#2
SF#4SF#4
. . .
half frame
DwPTS: Downlink Pilot time Slot
UpPSS: Uplink Pilot Time Slot
GP: Guard Period to separate between UL/DL
Downlink Subframe
Uplink Subframe
Frame Type 2 (TS 36.211-900; 4.2) each radio frame consists of 2 half frames Half-frame = 5 ms = 5 Sub-frames of 1 ms UL-DL configurations with both 5 ms & 10 ms DL-to-UL switch-point periodicity are supported Special subframe with the 3 fields DwPTS, GP & UpPTS; length of DwPTS + UpPTS +GP = 1
subframe DL / UL ratio can vary from 1/3 to 8/1 according to service requirements of the carrier
SF#0SF#0 Dw
PTS
Dw
PTS
GPGP
UpP
TSU
pPTS SF
#2SF#2
SF#4SF#4
subframe
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Subframe structure & CP length
Short cyclic prefix:
Long cyclic prefix:
Copy= Cyclic prefix
= Data
5.21 s
16.67 s
Subframe length: 1 ms for all bandwidths Slot length is 0.5 ms
1 Subframe= 2 slots Slot carries 7 symbols with normal CP or 6 symbols with long CP
CP length depends on the symbol position within the slot: Normal CP: symbol 0 in each slot has CP = 160 x Ts = 5.21s;
remaining symbols CP= 144 x Ts = 4.7s Extended CP: CP length for all symbols in the slot is 512 x Ts = 16.67s
Ts: sampling time of the overall channel basic Time Unit = 32.5 nsec
Ts =1 sec
Subcarrier spacing X max FFT size
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Resource Block and Resource Element
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 60 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 60 1 2 3 4 5 6 0 1 2 3 4 5 6
0 1 2 3 4 5 6 0 1 2 3 4 5 6
Subcarrier 1
Subcarrier 12
180
KH
z
1 slot 1 slot
1 ms subframe
RB
Resource Element
Physical Resource Block PBR or Resource Block RB: 12 subcarriers in frequency domain x 1 slot period in time domain Capacity allocation based on Resource Blocks
Resource Element RE: 1 subcarrier x 1 symbol period theoretical min. capacity allocation unit 1 RE is the equivalent of 1 modulation
symbol on a subcarrier, i.e. 2 bits (QPSK), 4 bits (16QAM), 6 bits (64QAM).
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Physical Resource Blocks
....
12 subcarriers
Time
Frequency
0.5 ms slot
1 ms subframeor TTI
Resource block
During each TTI, resource blocks for different UEs are scheduled in the eNodeB
During each TTI, resource blocks for different UEs are scheduled in the eNodeB
In both the DL & UL direction, data is allocated to users in terms of resource blocks (RBs).
a RB consists of 12 consecutive subcarriers in the frequency domain, reserved for the duration of 0.5 ms slot.
The smallest resource unit a scheduler can assign to a user is a scheduling block which consists of two consecutive resource blocks
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LTE Channel Options
Bandwidth options: 1.4, 1.6, 3, 3.2, 5, 10, 15 and 20 MHzBandwidth options: 1.4, 1.6, 3, 3.2, 5, 10, 15 and 20 MHz
Subcarriers in frequency domain (15 kHz or 7.5 kHz subcarrier spacing)
Channel bandwidth (MHz)
Number of subcarriers
Number of resource blocks
1.4
72
6
3
180
15
5
300
25
10
600
50
15
900
75
20
1200
100
Each channel bandwidth offers a certain number of subcarriers, or - expressed in another way - a certain number of resource blocks. From the table you can easily see that a resource block always occupies 12 subcarriers.
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DL Physical Resource Block
....
12 subcarriers
Time
0.5 ms slot
1 ms subframe
or TTI
DL reference signal
Reference signals position in time domain is fixed (symbol 0 & 4 / slot for Type 1 Frame) whereas in frequency domain it depends on the Cell ID
Reference signals are modulated to identify the cell to which they belong.
This signal, consisting of a known pseudorandom sequence, is required for channel estimation in the UEs. (like CPICH in WCDMA).
Note that in the case of MIMO transmission, additional reference signals must be embedded into the resource blocks.
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DL Physical Channels
PDSCH: Physical Downlink Shared Channel carries user data, L3 Signalling, System Information Blocks & Paging
PBCH: Physical Broadcast Channel for Master Information Block only
PMCH: Physical Multicast Channel for multicast traffic as MBMS services
PCFICH: Physical Control Format Indicator Channel indicates number of OFDM symbols for Control Channels = 1..4
PDCCH: Physical Downlink Control Channel carries resource assignment messages for DL capacity allocations & scheduling
grants for UL allocations
PHICH: Physical Hybrid ARQ Indicator Channel carries ARQ Ack/Nack messages from eNB to UE in respond to UL transmission
There are no dedicated channels in LTE, neither UL nor DL.
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UL Physical Channels
PUSCH: Physical Uplink Shared Channel Transmission of user data, L3 & L1 signalling (L1 signalling: CQI, ACK/NACKs, etc.)
PUCCH: Physical Uplink Control Channel Carries L1 control information in case that no user data are scheduled in this subframe
(e.g. H-ARQ ACK/NACK indications, UL scheduling request, CQIs & MIMO feedback). These control data are multiplexed together with user data on PUSCH, if user data are
scheduled in the subframe
PRACH: Physical Random Access Channel For Random Access attempts; SIBs indicates the PRACH configuration (duration;
frequency; repetition; number of preambles - max. 64)
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UL Physical Resource Block: DRS & SRS
....
12 subcarriers
Time
0.5 ms slot
1 ms subframeor TTI
Frequency
Sounding Reference Signal on last OFDM symbol of 1 subframe;Periodic or aperiodic
transmission
Sounding Reference Signal on last OFDM symbol of 1 subframe;Periodic or aperiodic
transmission
Demodulation Reference Signal in subframes that carry
PUSCH
Demodulation Reference Signal in subframes that carry
PUSCH
Note: when the subframe contains the PUCCH, the Demodulation
Reference Signal is embedded in a different way
Note: when the subframe contains the PUCCH, the Demodulation
Reference Signal is embedded in a different way
The Demodulation Reference Signal is transmitted in the thirdSC-FDMA symbol (counting from zero) in all resource blocks allocated to the PUSCH carrying the user data.
This signal is needed for channel estimation, which in turn is essential for coherentdemodulation of the UL signalin the eNodeB.
The Sounding Reference Signal SRS provides UL channel quality information as a basis for scheduling decisions in the base station. This signal is distributed in the last SC-FDMA symbol of subframesthat carry neither PUSCH nor PUCCH data. [SRS is always disabled in FDD RL20 and before.]
PUCCH: Physical UL Control Channel
SRS can be used to implement beamforming in TDD.
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b0 b1
QPSK
Im
Re10
11
00
01
b0 b1b2b3
16QAM
Im
Re
0000
1111
Im
Re
64QAM
b0 b1b2b3 b4 b5
3GPP standard defines the following options: QPSK, 16QAM, 64QAM in both directions (UL & DL)
UL 64QAM not supported in RL10 Not every physical channel is allowed to use any
modulation scheme: Scheduler decides which form to use depending on carrier
quality feedback information from the UE
Modulation Schemes
QPSK: 2 bits/symbol
16QAM: 4 bits/symbol
64QAM: 6 bits/symbol
QPSKPDCCH, PCFICH
Physical channel
Modulation
PDSCH QPSK, 16QAM, 64QAM
PMCH QPSK, 16QAM, 64QAM
PBCH QPSK
PHICH BPSKPUSCH QPSK,
16QAM, 64QAM
PUCCH BPSK and/or QPSK
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Module Contents
OFDM Basics OFDM & Multipath Propagation: The Cyclic Prefix OFDM versus OFDMA OFDM Weaknesses OFDM Key Parameters SC-FDMA LTE Air Interface Physical Layer Physical Layer Overhead LTE Measurements Frequency Variants RRM Overview VoIP in LTE
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DL Reference Signal Overhead
Reference Signal (RS)- If 1 Tx antenna*: 4 RSs per PRB- If 2 Tx antenna*: there are 8 RSs per PRB- If 4 Tx antenna*: there are 12 RSs per PRB
Example below: Normal CP (84 RE) & 2 Tx antenna*, DL RS overhead = 8 / 84 = 9.52 %
* with 1/2/4 Antenna PortsPRB: Physical Resource Block
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Synchronization Signals Overhead
Primary Synchronization Signal (PSS) - occupies 144 Resource Elements per frame (20 timeslots); i.e. (62 subcarriers + 10
empty Resource Elements) x 2 times/frameExample: Normal CP, 10 MHz bandwidth; PSS overhead = 144 / (84 20 50) = 0.17 %
Secondary Synchronization Signal (SSS) Identical calculation to PSS; same overhead as for PSS
2 3 4 5 7 8 9 10
1 2 3 4 5 6 7
1 2 3 4 5 6
10ms Radio frame
1ms Subframe SSSPSS
0.5ms = 1 slot
Normal CP
Extended CP
PSS & SSS frame + slotstructure in time domain
(FDD case)
checking for SSSat 2 possible positions CP length
checking for SSSat 2 possible positions CP length
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The combination of PDCCH, PCFICH & PHICH occupies the first 1, 2 or 3 symbols per TTI*
Resource Elements reserved for
Reference Symbols(2 antenna port case)
Control ChannelRegion (1-3 OFDM symbols*)
12 s
ubca
rrie
rs
Freq
uenc
y
TimeData Region
One subframe (1ms)
PDCCH, PCFICH & PHICH overhead (1/2)
* up to 4 OFDM symbols in case of 1.4 MHz bandwidth
12 x7x2 = 12 x7 reflects the number of RE per RB and x2 reflects there are 2 RBsper TTI
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PDCCH, PCFICH & PHICH overhead (2/2)
The number of RE occupied per 1 ms TTI is given by (12 y x), where: y depends upon the number of OFDM symbols per TTI (1, 2 or 3*) occupied by
Control Channels x depends upon the number of RE already occupied by the Reference Signal
x = 2 for 1 Tx antenna (Antenna Port) x = 4 for 2 Tx antennas (Antenna Ports) x = 4 for 4 Tx antennas (Antenna Ports) when y = 1 x = 8 for 4 Tx antennas (Antenna Ports) when y = 2 or 3
Example: in the case of normal CP, 2 Antenna Ports & 3 OFDM symbols occupied by Control Channels:
Control Channel Overhead = (12 3 - 4) / (12 7 2) = 19.05%
* up to 4 OFDM symbols in case of 1.4 MHz bandwidth
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PBCH Overhead
Occupies (288* x) Resource Elements (REs) per 20 timeslots per transmit antennaThe value of x depends upon the number of REs already occupied by the Reference Signal:x = 12 for 1 Tx antenna, x = 24 for 2 Tx antennas & x = 48 for 4 Tx antenna- Example: normal CP, 2 Tx antennas, 10 MHz bandwidth;
PBCH Overhead = (288 24) / (84 20 50) = 0.31%
72 s
ubca
rrie
rs
Repetition Pattern of PBCH = 40 ms
one radio frame = 10 ms
PBCH* PBCH uses central 72 Subcarrier over 4 OFDM symbols in Slot 1
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UL Demodulation Reference Signal Overhead (1/2)
Demodulation Reference Signal (DRS)
The DRS is sent on the 4thOFDM symbol of each RB occupied by the PUSCH.
PUCCH
PUCCH
PUSCH
UL DRS occupies the whole allocated band except 2 RB bandwidth in the both end.Reference signal: 12 RE (per RB) x (50-2) RBs not dedicated to PUCCH /(84 x50) =13.14%
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Example:For 1.4 MHz Channel Bandwidth, the PUCCH occupies 1 RB per Slot.The number of RE per RB is 84 when using the normal CP. This means the DRS overhead* is: ((6-1) 12)/(6 84) = 11.9 %
Channel BW PUCCH RB/slot DRS Overhead*1.4 MHz 1 ((6-1) 12) / (6 84) = 11.9 %3 MHz 2 ((15-2) 12) / (15 84) = 12.38 %5 MHz 2 ((25-2) 12) / (25 84) = 13.14 %10 MHz 4 ((50-4) 12) / (50 84) = 13.14 %15 MHz 6 ((75-6) 12) / (75 84) = 13.14 %20 MHz 8 ((100-8) 12) / (100 84) = 13.14 %
UL DRS Overhead (2/2)
* for normal CP
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PRACH Overhead
PRACH PRACH uses 6 Resource Blocks in the frequency domain. The location of those resource blocks is dynamic. Two parameters from RRC layer define it:
PRACH Configuration Index: for Timing, selecting between 1 of 4 PRACH durations and defining if PRACH preambles can be send in any radio frame or only in even numbered ones
PRACH Frequency offset: Defines the location in frequency domain PRACH Overhead calculation: 6 RBs * RACH Density / (#RB per TTI) x 10 TTIs per frame
RACH density: how often are RACH resources reserved per 10 ms frame i.e. for RACH density: 1 (RACH resource reserved once per frame)
Channel BW PRACH Overhead1.4 MHz (6 1) / (6 10) = 10 %3 MHz (6 1) / (15 10) = 4 %5 MHz (6 1) / (25 10) = 2.40 %10 MHz (6 1) / (50 10) = 1.20 %15 MHz (6 1) / (75 10) = 0.8 %20 MHz (6 1) / (100 10) = 0.6 %
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PUCCH Overhead PUCCH Ratio between the number of RBs used for PUCCH and the total number of RBs in frequency
domain per TTIChannel BW PUCCH RB/slot PUCCH Overhead
1.4 MHz 1 1 / 6 = 16.67 %3 MHz 2 2 / 15 = 13.33 %5 MHz 2 2 / 25 = 8 %10 MHz 4 4 / 50 = 8 %15 MHz 6 6 / 75 = 8 %20 MHz 8 8 / 100 = 8%
Time
Tota
l UL
Ban
dwith
PUCCH
PUCCH
PUSCH
1 subframe = 1ms
Freq
uenc
y
12 s
ubca
rrie
rs
PUCCH carries UCI(Uplink Control Information), ie, Aperiodic CQI reports and ACK/NACK
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Physical Layer Overhead Example
Example of overhead: DL 2Tx 2RX UL 1TX - 2RX PRACH in every frame 3 OFDM symbols for PDCCH
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Module Contents
OFDM Basics OFDM & Multipath Propagation: The Cyclic Prefix OFDM versus OFDMA OFDM Weaknesses OFDM Key Parameters SC-FDMA LTE Air Interface Physical Layer Physical Layer Overhead LTE Measurements Frequency Variants RRM Overview VoIP in LTE
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LTE Measurements
Physical layer measurements have not been extensively discussed in the LTE standardization. They could change. Intra LTE measurements ( from LTE to LTE) UE measurements
CQI measurements Reference Signal Received Power (RSRP) Reference Signal Received Quality ( RSRQ)
eNB measurements Non standardized (vendor specific): TA, Average RSSI, Average SINR, UL CSI,
detected PRACH preambles, transport channel BLER Standardized: DL RS Tx Power, Received Interference Power, Thermal Noise Power
Measurements from LTE to other systems UE measurements are mainly intended for Handover.
UTRA FDD: CPICH RSCP, CPICH Ec/No and carrier RSSI GSM: GSM carrier RSSI UTRA TDD: carrier RSSI, RSCP, P-CCPCH CDMA2000: 1xRTT Pilot Strength, HRPD Pilot Strength
CSI: Channel State Information (received power per PRB)TA: Timing Advance
List of detected preambles: The eNB shall report a list of detected PRACH preambles to higher layers. Higher layer utilize this info for the RACH procedure Transport BLER: The ACK/ NACKs for each transmission of the HARQ process are reported to the MAC. Based on these ACK/NACKs the higher layers compute the BLER for RRM issues.TA: The eNB needs to measure the initial timing advance (TA) of the uplink channels based on the RACH preamble Average RSSI: Measured in UL by eNB. It can be used as a level indicator for the UL power control. The RSSI measurements are all UE related and shall be separately performed for ( TTI intervals) UL data allocation (PUSCH) UL control channel (PUCCH) Sounding reference signal (SRS)Average SINR: In UL the eNB measures SINR per UE. The average SINR can be used as a quality indicator for the UL power control UL CSI: channel state information per PRB for each UE. The CSI shall be the received signal power averaged per PRB.
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UE Measurements: RSRP & RSRQ
RSRP (Reference Signal Received Power) Average of power levels (in [W]) received across all Reference Signal symbols
within the considered measurement frequency bandwidth. UE only takes measurements from the cell-specific Reference Signal elements of
the serving cell If receiver diversity is in use by the UE, the reported value shall be equivalent to
the linear average of the power values of all diversity branches Reporting range -44-133 dBm
RSRQ ( Reference Signal Received Quality) Defined as the ratio NRSRP/(E-UTRA carrier RSSI), where N is the number of
RBs of the E-UTRA carrier RSSI measurement bandwidth. The measurements in the numerator and denominator shall be made over the same set of resource blocks
Reporting range -3-19.5dB
Seems that it has been removed: E-UTRA Carrier Received Signal Strength Indicator, comprises the total received wideband power observed by the UE from all RS symbols for antenna port 0, including co-channel serving and non-serving cells, adjacent channel interference, thermal noise etc.
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eNodeB Measurements
DL Reference Signal Transmitted Power Average of power levels (in [W]) transmitted across all Reference Signal symbols
within the considered measurement frequency bandwidth Reference point for the DL RS TX power measurement: TX antenna connector The DL RS TX power signaled to the UE is not measured, it is just an eNB internal
settingReceived Interference Power: Received interference power, including thermal noise, within one PRBs bandwidthThermal noise power: No x W Thermal noise power within the UL system bandwidth (consisting of variable # of
resource blocks) No: white noise power spectral density on the uplink carrier frequency and W: denotes
the UL system bandwidth. Optionally reported with the Received Interference Power Reference point: RX antenna connector In case of receiver diversity, the reported value is the average of the power in the
diversity branches
Thermal noise power and Received Interference Power are measured for the same period of time.
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Module Contents
OFDM Basics OFDM & Multipath Propagation: The Cyclic Prefix OFDM versus OFDMA OFDM Weaknesses OFDM Key Parameters SC-FDMA LTE Air Interface Physical Layer Physical Layer Overhead LTE Measurements Frequency Variants RRM Overview VoIP in LTE
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LTE Frequency Variants in 3GPP FDD
123
45
789
62x25
2x752x602x60
2x70
2x45
2x352x35
2x10824-849
1710-17851850-19101920-1980
2500-2570
1710-1755
880-9151749.9-1784.9
830-840
BW[MHz] Uplink [MHz]
869-894
1805-18801930-19902110-2170
2620-2690
2110-2155
925-9601844.9-1879.9
875-885
Downlink [MHz]
10 2x60 1710-1770 2110-217011 2x25 1427.9-1452.9 1475.9-1500.9
1800
2600
900
US AWS
UMTS coreUS PCS
US 850Japan 800
Japan 1700
Japan 1500Extended AWS
Europe Japan Americas
788-798 758-768777-787 746-756
Japan 800
US7002x102x1013
12 2x18 698-716 728-746
14 US700
US700
815 830 860 875 704 716 734 746
2x152x1217
18US700
Band
UHF (TV)832 862 791 821 830 845 875 890
2x302x1519
20Japan 800
1626.5 1660.5 1525 15592x34241447.9 1462.9 1495.9 1510.92x1521
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LTE Frequency Variants - TDD
333435
3637
3940
381x20
1x601x151x20
1x40
1x60
1x100
1x501910 - 1930
1850 - 19102010 - 20151900 - 1920
1880 - 1920
1930 - 1990
2300 - 2400
2570 - 2620
BW[MHz] Frequency[MHz]
UMTS TDD 1
UMTS TDD 2US PCS
US PCSUS PCS
Euro midle gap 2600China TDDChina TDD
Band
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Module Contents
OFDM Basics OFDM & Multipath Propagation: The Cyclic Prefix OFDM versus OFDMA OFDM Key Parameters OFDM Weaknesses SC-FDMA LTE Air Interface Physical Layer Physical Layer Overhead LTE Measurements Frequency Variants RRM Overview VoIP in LTE
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RRM building blocks & functionsOverview
Scope of RRM:Management & optimized utilization of the radio resources:
Increasing the overall radio network capacity & optimizing quality
Provision for each service/bearer/user an adequate QoS (if applicable)
RRM located in eNodeBMIMO Ctrl., LA & schedulers act on TTI basis.
NSN LTE RRM Framework consists of RRM building blocks, RRM functions and RRM algorithms.L3 RRM: ICIC: Selects certain parts of the Frequency Spectrum of the LTE Carrier. Exclusively for PDSCH and PUSCH on Cell Basis. Remaining channels not affected.DRX/DTX algorithm: To support provisioning of measurement gaps for Inter-RAT-HO and DRX/DTX mode in later product releases. Not supported in RL09.Differences with RRM WCDMA: Softer and Soft handovers are not supported by the LTE system LTE requirements on power control are much less stringent due to the different nature of LTE radio interface i.e. OFDMA (WCDMA requires fast power control to address the Near-Farproblem and intra-frequency interferences)On the other hand LTE system requires much more stringent timing synchronization for OFDMA signals.
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LTE RRM: Scheduling (1/4)
Motivation Bad channel condition avoidance
OFDMA
The part of total available channel experiencing bad channel condition (fading)
can be avoided during allocation procedure.
CDMA
Single Carrier transmission does not allow to allocate only particular frequency parts. Every fading gap
effects the data.
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Scheduler (UL/DL) (2/4)
Cell-based scheduling (separate UL/DL scheduler per cell) Scheduling air interface resource on a 1ms 12sub-carrier (PRB pair) basis Scheduler controls UEs & assigns appropriate grants per TTI Proportional Fair (PF) resource assignment among UEs Uplink:
Channel unaware UL scheduling based on random frequency allocation Descending resource handling priority in UL for
1. Hybrid ARQ retransmission2. Random access procedure3. Signaling radio bearer with or without data radio bearer4. Scheduling request5. Conversational voice data6. Data radio bearer
Downlink: Channel aware DL scheduling - Frequency Domain Packet Scheduling (FDPS) -
based on CQI with resources assigned in a fair manner
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Downlink Scheduler (3/4)Algorithm
Determine which PRBs are available (free) and can be allocated to UEs
Allocate PRBs needed for common channels like SIB, paging, and random access procedure (RAP)
Final allocation of UEs (bearers) onto PRB. Considering only the PRBs available after the previous steps
Pre-Scheduling: All UEs with data available for transmission based on the buffer fill levels
Time Domain Scheduling: Parameter MAX_#_UE_DL decides how many UEs are allocated in the TTI being scheduled
Frequency Domain Scheduling for Candidate Set 2 UEs: Resource allocation in Frequency Domain including number & location of allocated PRBs
Evaluation of available resources (PRBs/RBGs ) for dynamic allocation on PDSCH
Resource allocation and schedulingfor common channels
DL scheduling of UEs :Scheduling of UEs /bearers to PRBs /RBGs
Start
End
Pre -Scheduling :Select UEs eligible for scheduling
-> Determination of Candidate Set 1
Time domain schedulingof UEs according to simple criteria
-> Determination of Candidate Set 2
Start
End
Frequency domain schedulingof UEs /bearers
-> PRB /RBG allocation to UEs /bearers
SIB: System Information BroadcastMAX_#_UE_DL depends on the bandwidth: 7UEs (5 MHz), 10UEs (10MHz) and 20 UEs (20MHz)
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Uplink Scheduler (4/4)Algorithm
Evaluation of the #PRBs that will be assigned to UEs Available number of PRBs per user: resources are assigned via PRB groups (group of
consecutive PRBs)Time domain: Max_#_UE_UL which can be scheduled per TTI time frame is restricted by an O&M
parameter and depends on the bandwidth: 7 UEs (5 MHz), 10 UEs (10MHz) and 20 UEs(20MHz)
Frequency Domain: Uses a random function to assure equal distribution of PRBs over the available frequency
range (random frequency hopping)
a) b)
Feature ID(s): LTE45
Example of allocation in frequency domain:
Full Allocation: All available PRBs are assigned to the scheduled UEs per TTI
Fractional Allocation: Not all PRBs are assigned. Hopping function handles unassigned PRBs as if they were allocated to keep the equal distribution per TTI
PRBs allocated for PRACH, PUCCH are excluded for PUSCH scheduling
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LTE RRM: Link Adaptation by AMC (UL/DL) (1/6)
Motivation of link adaptation: Modify the signal transmitted to and by a particular user according to the signal quality variation to improve the system capacity & coverage reliability.
It modifies the MCS (Modulation & Coding Scheme) & the transport block size (DL) and ATB (UL)
If SINR is good then higher MCS can be used more payload per symbol more throughput.
If SINR is bad then lower MCS should be used (more robust) Flexi Multiradio BTS performs the link adaptation for DL on a TTI basis The selection of the modulation & the channel coding rate is based:
DL data channel: CQI report from UE UL: BLER measurements in Flexi LTE BTS
LTE31: Link Adaptation by AMC
Optimizing air interface efficiency
Adaptive Transmission Bandwidth (ATB): Calculates maximum number of PRBsthat UL SCH can assigned to a particular UE taking into account UE QoS profile and available UE power headroom
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Link Adaptation / AMC for PDSCH (2/6)
Procedure: Initial MCS is provided by O&M
(parameter INI_MCS_DL) & is set as default MCS
If DL AMC is not activated (O&M parameter ENABLE_AMC_DL) the algorithm always uses this default MCS
If DL AMC is activated HARQ retransmissions are handled differently from initial transmissions (For HARQ retransmission the same MCS has to be used as for the initial transmission)
A MCS based on CQI reportingfrom UE , shall be determined for the PRBs assigned to UE as indicated by the DL scheduler
yes
no
no
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Link Adaptation / AMC for PUSCH (3/6)
Functionality UL LA is active by default but can be deactivated by O&M parameters. If not active,
the initial MCS is used all the time UE scope Two parallel algorithms adjust the MCS to the radio channel conditions:
Inner Loop Link Adaptation (ILLA): Slow Periodic Link adaptation (20-500ms) based on BLER measurements
from eNodeB (based on SINR in future releases) Outer Loop Link Adaptation (OLLA): event based
In case of long Link Adaptation updates and to avoid low and high BLER situations, the link adaptation can act based on adjustable target BLER:
- Emergency Downgrade if BLER goes above a MAX BLER threshold (poor radio conditions)
- Fast Upgrade if BLER goes below of a MIN BLER threshold (excellent radio conditions)
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Downlink fast
1 TTI channel aware
CQI based MCS selection
1 out of 0-28 output
MCS TBS
up to 64QAM support
Uplink slow periodical
~30ms channel partly aware
average BLER based MCS adaptation
+/- 1 MCS correction output
MCS ATB
up to 16 QAM support
Comparison: DL & UL Link adaptation for PSCH (4/6)
MCS: Modulation & Coding SchemeTBS: Transport Block SizeATB: Automatic Transmission Bandwidth
Adaptive Transmission Bandwidth (ATB): Responsible for defining maximum number of PRBs that can be assigned to a particular UE by UL SCH
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Outer Link Quality Control (OLQC) (5/6)
Feature: CQI Adaptation (DL) CQI information is used by the scheduler & link adaptation in such a way that a certain
BLER of the 1st HARQ transmission is achieved CQI adaptation is the basic mean to control Link Adaptation behaviour and to remedy UE
measurement errors Only used in DL Used for CQI measurement error compensation
CQI estimation error of the UE CQI quantization error or CQI reporting error
It adds a CQI offset to the CQI reports provided by UE. The corrected CQI report is provided to the DL Link adaptation for further processing
CQI offset derived from ACK/NACK feedback
Optimize the DL performance
Feature ID(s): LTE30
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Support of aperiodic CQI reports (6/6)
Functionality Aperiodic CQI reports scheduled in addition to periodic reports
Periodic CQI reports on PUCCH Aperiodic CQI reports on PUSCH
Description Controlled by the UL scheduler
Triggered by UL grant indication (PDCCH) Basic feature
Feature ID(s): LTE767
Benefits Not so many periodic CQIs on PUCCH
needed Allow frequent submission of more detailed
reports (e.g. MIMO, frequency selective parts)
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LTE RRM: Power Control (1/4)
Downlink: There is no adaptive or dynamic power control in DL but semi-static power
setting
eNodeB gives flat power spectral density (dBm/PRB) for the scheduled resources:
The power for all the PRBs is the same If there are PRBs not scheduled that power is not used but the power of the
remaining scheduled PRBs doesnt change: Total Tx power is max. when all PRBs are scheduled. If only 1/2 of the PRBs are
scheduled the Tx power is 1/2 of the Tx power max ( i.e. Tx power max -3dB)
Semi-static: PDSCH power can be adjusted via O&M parameters Cell Power Reduction level CELL_PWR_RED [0...10] dB attenuation in 0.1 dB steps
Improve cell edge behaviour, reduce inter-cell interference & power consumption
Feature ID(s): LTE27
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Power Control (2/4)
Uplink: UL PC is a mix of Open Loop Power Control & Closed Loop Power Control:
Closed Loop PC component f(i): Makes use of feedback from the eNB. Feedback are TCP commands send via PDCCH to instruct the UE to increase or decrease its Tx power
Improve cell edge behaviour, reduce inter-cell interference and power consumption
Feature ID(s): LTE27<E28
])}[()()()())((log10,min{)( _010 dBmifiPLjjPiMPiP TFPUSCHPUSCHCMAXPUSCH ++++=
UL Power control is Slow power control: No need for fast power control as in 3G:
if UE Tx power was high it incremented the co-channel for other UEs.
In LTE all UEs resources are orthogonal in frequency & time
TPC: Transmit Power Control
WCDMA: If UE Tx power was high it increased the co-channel interference for other UEsOpen loop suffers from errors in UE path loss measurement and tx power setting whereas closed loop PC is less sensitive to errorsControl over power spectral density, not absolute power. The power is changed by the UL scheduler by varying the bandwidth granted. The power per Hz remains constant.
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Power Control (3/4)
Uplink (cont.): UL PC is a mix of Open Loop Power Control & Closed Loop Power Control:
PCMAX: max. UE Tx power according to UE power class; e.g. 23dBm for class 3 MPUSCH: # allocated PRBs. The UE Tx Power is increased proportionally to the # of allocated
RBs. Remaining terms of the formula are per RB
P0_PUSCH: eNB received power per RB when assuming path loss 0 dB. Depends on : Path loss compensation factor. Three values:
= 0, no compensation of path loss = 1, full compensation of path loss (conventional compensation) { 0 ,1 } , fractional compensation
PL: DL Path loss calculated by the UE Delta_TF: increases the UE Tx power to achieve the required SINR when transmitting a
large number of bits per RE. It links the UE Tx power to the MCS.
Feature ID(s): LTE27<E28
])}[()()()())((log10,min{)( _010 dBmifiPLjjPiMPiP TFPUSCHPUSCHCMAXPUSCH ++++=
PL calculated by UE using a combination of RSRP measurements and knowledge of the RS transmit power (broadcasted in SIB2)Power control does not control the absolute UE Tx. power but the Power Spectral Density (PSD), power per Hz, for a device The PSDs at the eNodeB from different users have to be close to each other so the receiver doesnt work over a large range of powers.Different data rates mean different tx bandwidths so the absolute Tx power of the UE will also change. PC makes that the PSD is constant independently of the txbandwidth
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Conventional & Fractional Power Control (4/4)
Conventional PC schemes: Attempt to maintain a constant SINR at the receiver UE increases the Tx power to fully compensate for increases in the path loss
Fractional PC schemes: Allow the received SINR to decrease as the path loss increases. UE Tx power increases at a reduced rate as the path loss increases. Increases in
path loss are only partially compensated. [+]: Improve air interface efficiency & increase average cell throughputs by reducing
Intercell interference 3GPP specifies fractional power control for the PUSCH with the option to disable it &
revert to conventional based on
Conventional Power Control: =1If Path Loss increases by 10 dB the UE Tx power increases by 10 dB
Fractional Power Control: { 0 ,1}If Path Loss increases by 10 dB the UE Txpower increases by < 10 dB
UE TxPower UE Tx
Power
UL SINR UL SINR
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LTE RRM: Radio Admission Control (RAC)
Objective: To admit or reject requests for establishment of Radio Bearers (RB) on a cell basis
Based on number of RRC connections and number of active users per cell Non QoS aware Both can be configured via parameters
RRC connection is established when the SRBs have been admitted & successfully configured
UE is considered as active when a Data Radio bearer (DRB) is established Upper bound for maximum number of supported connections depends on the
BB configuration of eNB : RL10: support for 200, 400 & 800 active users respectively in 5, 10 & 20 MHz RL20: up to 840 active users in 20MHz
Handover RAC cases have higher priority than normal access to the cell
At reception of the HO request message the RAC decides in an all-or-nothingmanner on the admission / rejection of the resources used by the UE in the source cell (prior to HO). 'All-or-nothing' manner means that either both SRB AND (logical) DRB are admitted or the UE is rejected. RL09 all SRB are admitted.SRB: between UE and eNB.This is introduced in RL10. In RL09, All RRC connection setup request are admitted by default to avoid RAC complexity
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LTE RRM: MIMO / Antenna Control (1/5)Transmit diversity for 2 antennas
Benefit: Diversity gain, enhanced cell coverage Each Tx antenna transmits the same stream of data with Receiver gets
replicas of the same signal which increases the SINR. Synchronization signals are transmitted only via the 1st antenna eNode B sends different cell-specific Reference Signals (RS) per antenna It can be enabled on cell basis by O&M configuration Processing is completed in 2 phases:
Layer Mapping: distributing a stream of data into two streams Pre-coding: generation of signals for each antenna port
Additional antenna specific coding is applied to the signals before transmission to increase the diversity effect. Transmit diversity is open loop (it doesnt take any advantage of any feedback from the UE as weights are fixed). It is simpler to implement and doesnt have the overhead generated by the feedback information. Tx diversity is the solution for open loop spatial multiplexing when transferring a single code word.
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S1
S2
Spatial multiplexing (MIMO) for 2 antennas (2/5)
Benefit: Doubles peak rate compared to 1Tx antenna
Spatial multiplexing with 2 code words Supported physical channel: PDSCH
Two code words (S1+S2) are
transmitted in parallel to 1 UE double peak rate
Layer Mapping
L1
L2
PrecodingMap onto Resource Elements
Map onto Resource Elements
OFDMA
OFDMA
Modulation
Modulation
Code word 1
Code word 2
Scale
W2
W1
2 code words transferred when channel conditions are good
Signal generation is similar to Transmit Diversity: i.e. Layer Mapping & Precoding
Can be open loop or closed loop depending if the UE provides feedback
RL20: LTE703: DL adaptive closed loop MIMO
The cyclic delay operation for the second antenna causes a linear phase shift along the frequency dimension. Thus, summing the cyclically delayed signal in the receiver and the un-delayed signal from the first antenna causes a frequency selective fading pattern UE provides feedback in terms of:
CQIRank Indication (RI) number of layers to usePrecoding Matrix Indicator (PMI) set of weights to apply during precoding
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Precoding (3/5)
Precoding generates the signals for each antenna port Precoding is done multiplying the signal with a precoding matrix selected from a
predefined codebook known at the eNB and at the UE side Closed loop: UE estimates the radio channel, selects the best precoding matrix
(the one that offers maximum capacity) & sends it to the eNB Open loop: no need for UEs feedback as it uses predefined settings for Spatial
Multiplexing & precoding
Pre-coding codebook for 2 Tx antenna case
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DL adaptive MIMO for 2 antennas (4/5)
Benefit: High peak rates (2 code words) & good cell edge performance (single code word)
2 TX antennas Dynamic selection between
Transmit diversity Spatial Multiplexing
Supported physical channel: PDSCH Dynamic switch considers the UE specific
link quality, UE capability, etc. Enabled/disabled on cell level (O&M)
If disabled case either static spatial multiplexing or static Tx diversity can be selected for the whole cell (all UEs)
2 code words (A+B) are transmitted in parallel to 1 UE which doubles the peak rate
1 code word A is transmitted via 2
antennas to 1 UE; improves the LiBu*
AB
A
(RL10) LTE70: DL Adaptive Open Loop MIMO
(RL20) LTE703: DL Adaptive Closed Loop MIMO, utilising PMI report for precoding
* LiBu: Link Budget
Note: CQI adaptation needs to be supported/enabled ;Tx diversity needs to be supported/enabled. MIMOThis feature was introduced in RL10. In LTE70, UE radio capabilities, andUECQI, andUE rank information, are considered.Performance counter for transmission mode usage is supported per cell
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MIMO, DL channels & RRM Functionality (5/5)
Available MIMO options vs. channel type Options for Transmit Diversity (2 Tx):
Control Channels PDSCH
Options for spatial Multiplexing: Only DL PDSCH
MIMO is SW feature
Channel can be configured to use MIMO modeChannel cannot be configured to use MIMO mode
In UL, Flexi eNodeB has 2Rx Div. : Maximum Ratio Combining
Benefit: increase coverage by increasing the received signal strength and quality
RRM MIMO Mode Control Functionality Refers to switch between: Tx Diversity (single stream) MIMO Spatial Multiplexing (single / dual stream) 1x1 SISO / 1x2 SIMO
Provided by eNB only for DL direction
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LTE RRM: Connection Mobility Control Handover Types
Intra-RAT handover Intra eNodeB (Intra or Inter Frequency / Band) Inter eNodeB (Intra or Inter Frequency / Band)
If X2 available Data forwarding High performance for 15120 km/h Optimized performance for 015 km/h
If no X2 HO via S1 interface (LTE54, RL20)
Inter-RAT Handover Support Plan PS domain only RL20: LTE CDMA2000 (Idle) RL30: LTE WCDMA (PS InterRAT HO & SRVCC) RL30: LTE GSM (SRVCC & NACC)
RU20: W(PS domain)InterRAT HOL is nominally supported, but NED has no relevant parameters.RU30 plan: WHOL.SRVCC(single radio voice call continuity): function that is responsible for the handover from a packet-switched access to a circuitswitched access
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Intra frequency handover via X2
Basic Mobility Feature Event triggered handover based
on DL measurements (ref. signals)
Network evaluated HO decision Operator configurable
thresholds for coverage based & best cell based handover
Data forwarding via X2 Radio Admission Control (RAC)
gives priority to HO related access over other scenarios S1
S1 X2
MMES-GWP-GW
Feature ID(s): LTE53
A reliable and lossless mobility
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Intra LTE Handover via S1
Extended mobility option to X2 handover
Handover in case of no X2 interface between eNodeBs, e.g. multi-vendor scenarios eNodeBs connected to different CN elements Operator configurable thresholds for coverage based (A5) and best cell based (A3) handover
DL Data forwarding via S1
Feature ID(s): LTE54
RL20
Admission Control gives priority to HO related access over other scenarios
Blacklists
this feature allows to hand over a UE in RRC_Connected mode between two LTE cells operating on different carriers (frequencies/bands).
the trigger for this procedure is: better neighbor cell (frequency) coverage;better neighbor cell (frequency) quality; limited serving
cell (frequency) and sufficient neighbor cell (frequency) coverageintra LTE inter-frequency handover is classified as a:
hard handover: connection to one cell only at the same time gap assisted measurements are usually requirednetwork controlled and UE assisted handover: network takes decision based on measurements delivered by UEbackward handover: The resources at target cell (frequency) are reserved in advance
handover performed via X2 or S1 interface: data forwarding between serving and target eNB may be applied
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Inter Frequency Handover
Multi-band mobility
Network controlled Event triggered based on DL
measurement RSRP and RSRQ Inter frequency measurements
triggered by events A1/A2 Operator configurable thresholds for
coverage based (A5),best cell based (A3) handover
Service continuity for LTE deployment in different frequency bands as well as for LTE deployments within one frequency band but with different center frequencies
Blacklists
Feature ID(s): LTE55
RL20
Requires feature Redirect LTE to other technologies (LTE _423) i.e. RRC Connection Release with Redirect (RL10 feature): message is triggered based on source cell downlink RSRP measurements (even A2)A1: start A2:stop inter frequency measurements
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Inter RAT Handover to WCDMA
Coverage based inter-RAT PS handover Only for multimode devices supporting
LTE and WCDMA Event triggered handover based on DL
measurement RSRP (reference signal received power)
Operator configurable RSRP threshold Network evaluated HO decision Target cells are operator configurable An ANR functionality may be applied
optionally
Feature ID(s): LTE56
Blacklisting eNB initiates handover via EPC
In RL30 Plan
source cell thresholds (RSRP), target cell thresholds (RSCP, EcN0), hysteresis, time to trigger and speed dependent scaling are operator configurable. Handover preparationThe Flexi Multiradio BTS initiates a handover after receiving a measurement report form the UE by sending a S1AP:HANDOVER REQUIRED message to the MME.The Flexi Multimode BTS takes the first target cell indicated by the UE measurements for the handover.The MME responds to this with a S1AP:HANDOVER COMMAND message indicating that the resources at the target have been reserved.Handover executionThe Flexi Multiradio BTS sends after this a RRC:MobilityfromEUTRAcommandmessage to the UE, which forces to the to a WCDMA cell.The Flexi Multimode BTS performs handover retries to other target cells provided by the UE measurements in case of unsuccessful handovers.
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eNACC to GSM Network Assisted Cell Change to GSM
Service continuity to GSM
Network change from LTE to GSM in RRC Connected Mode when LTE coverage (RSRP) is ending
Prior to actual reselection process the measurements of 2G network are triggered
Only applicable for NACC capable devices
Inter RAT measurements triggered by events A1/A2
Operator configurable handover threshold (event B2)
Target cells for IRAT measurements can be configured by the operator
Blacklisting of target cells is supportedFeature ID(s): LTE442
In RL30 Plan
A1: activate interRAT measurementsA2: deactivate inter RAT measurementsB2:Inter RAT measurementsData forwarding is not supported for NACCMeasurements are triggered early enough to take to take the necessary actions on the UE side (in contrast to triggering the RL10 redirection procedure performed in critical conditions related to LTE coverage end without prior measurements of 2G/3G)
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Module Contents
OFDM Basics OFDM & Multipath Propagation: The Cyclic Prefix OFDM versus OFDMA OFDM Key Parameters OFDM Weaknesses SC-FDMA LTE Air Interface Physical Layer Physical Layer Overhead LTE Measurements Frequency Variants RRM Overview VoIP in LTE
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VoIP in LTE
Voice is still important in LTE CS voice call will not be possible in LTE since there is no CS core interface Voice with LTE terminals has a few different solutions The first voice solution in LTE can rely on Call Setup FallBack redirection
where LTE terminal will be moved to 2G/3G to make CS call The ultimate LTE voice solution will be VoIP + IMS
RL20
(RL20) LTE10: EPS Bearers for Conversational Voice(RL20) LTE562: Call Setup FallBack (CSFB)
IP Multimedia Subsystem, a set of specifications from 3GPP for delivering IP multimedia to mobile users VoIP: supported in RL20
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Single Radio Voice Call Continuity (SR-VCC)
LTE VoIP
3G CS voice
LTE VoIP
3G CS voice 3G CS voice 3G CS voice
Single Radio Voice Call Continuity (SR-VCC)
Options for voice call continuity when running out of LTE coverage 1) Handover from LTE VoIP to 3G CS voice
Voice Handover from LTE VoIP to WCDMA CS voice is called SR-VCC No VoIP needed in 3G
2) Handover from LTE VoIP to 3G VoIP VoIP support implemented in 3G
In RL40 Plan
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LTE Voice Evolution
VoIPLTEHSPAI-HSPA2G/3G
EPC
MSS
LTE broadband for high speed data Fast-Track VoLTE
IMS for enriched IP multimedia services
LTEHSPAI-HSPA
Simple upgrade of MSS with NVS (VoIP) function
Fully IMS compatible reuse of CS infra-structure for LTE VoIP capable handsets
SRVCC (HO LTE VoIP to 3G CS)
IMS-centric service architecture
Rich Communication Services with full multimedia telephony
Support for any access SRVCC (HO LTE VoIP
to 3G VoIP)
NVS
LTEHSPAI-HSPA2G/3G
EPCMSS
EPC
VoIP
NVSIMS
Main focus on LTE data CS Fallback to 2G/3G
CS access for voice Re-use existing MSC
Server system for voice
Evolution to IMSVoIP solution
Introduce NVSVoIP solution
MSS: Mobile Softwitching solutionNVS: Nokia Siemens Networks Voice ServerIMS: IP Multimedia Subsystem
CSPs can use their existing mobile softswitching and Nokia Siemens NetworksMobile VoIP Server (NVS) infrastructure to manage voice traffic over the LTE network, a function that will eventually be handled by IP Multimedia Subsystem (IMS). This gives CSPs an important time-to-market advantage.Fast Track VoLTE provides a transitional step between traditional networks and the all-IP world of LTE. The solution allows CSPs to exploit their existing circuit-switched mobile core network investments, while providing next-generation service. Investments in Fast Track VoLTE are fully re-usable when upgrading network architecture to IMS, thus reducing capital expenditure (CAPEX) in the long term.NVS: if MSC, NVS is provided by a SW upgrade and a minor HW addition.