LTE-Advanced Part 1: Carrier aggregation

Jyri Hmlinen, 2015 Department of Communications and Networking

Contents

Part 1: LTE-Advanced Carrier Aggregation (Rel.10/11) 1.1 Principles of Carrier Aggregation 1.2 Practical configurations and deployment issues 1.3 Primary and secondary Component Carriers 1.4 Radio Resource Management principles for Carrier Aggregation 1.5 Carrier Aggregation RLB example

1.1 Principles of Carrier Aggregation

Principle The target peak data rate of 1 Gbps in downlink and 500 Mbps

in uplink can be achieved with bandwidth extension from 20 MHz up to 100 MHz.

In LTE-Advanced this extension is achieved through carrier aggregation

By combining N Release 8 Component Carriers (CC), together to form N x LTE bandwidth, up to 5 x 20 MHz = 100 MHz operation bandwith could be obtained

Frequency

LTE-Advanced maximum configuration

RF band

R8 20 MHz

R8 20 MHz

R8 20 MHz

R8 20 MHz

R8 20 MHz

Component carrier (CC)

Backward compatibility with Rel.8/9

LTE Rel.8/9 terminals can receive/transmit only one component carrier

LTE-Advanced terminals may receive/transmit on multiple component carriers simultaneously to reach higher data rates.

5

Frequency R8/9 UE R8/9 UE R8/9 UE

LTE-A UE

1.4MHz 20MHz

R8/9 UE

Carrier Aggregation types

6

Frequency

Inter-band, non-contiguous CA

Band 1 Band 2

Frequency

Intra-band, non-contiguous CA

Band 1 Band 2

Frequency

Intra-band, contiguous CA

Band 1 Band 2

Contiguous vs non-contiguous CA

Rel-8/9 backward compatible carriers are the basic building blocks For an LTE Rel.8 terminal, each component carrier will appear as

an LTE carrier, while an LTE-Advanced terminal can use the total aggregated bandwidth

Regarding UE complexity, cost, capability, and power consumption, it is easier to implement contiguous CA with minimal changes to the physical layer structure of Rel.8-9 LTE.

In non-contiguous CA advanced RF components are needed in receiver in order to receive non-adjacent carriers.

Compared to non-contiguous CA, it is easier to implement resource allocation and management algorithms for contiguous CA.

Contiguous vs non-contiguous CA

Asymmetric number of component carriers in DL and UL is possible (later we define options)

Component carriers can apply any of the bandwidths supported in Rel.8 LTE

It is possible to use a single fast Fourier transform (FFT) module and a single radio frequency (RF) component to achieve contiguous CA for an LTE-Advanced UE unit, while providing backward compatibility to the LTE systems.

Contiguous vs non-contiguous CA

In practice it seems that in the low frequency band (< 4 GHz) it will be difficult to allocate continuous 100 MHz bandwidth for a mobile network.

The non-contiguous CA technique provides a practical approach to enable mobile network operators to fully utilize their current spectrum resources Thus, to use also currently unused scattered frequency bands and those

already allocated for some legacy systems, such as GSM and 3G systems.

It seems that for high capability LTE-Advanced terminals the deployment of advanced RF receiving units and multiple FFTs is unavoidable due to non-contiguous CA.

1.2 Practical configurations and deployment issues

Practical CA combinations

Due to practical (implementation) reasons CA was first defined only for some combinations of operating bands and component carriers.

The following terms and definitions for CA combinations are applied: Aggregated Transmission Bandwidth Configuration (ATBC): This

refers to the number of aggregated PRBs. CA bandwidth class (A, B and C): Refer to the combination of ATBC

and number of CCs. In Rel.10 and Rel.11 classes are: Class A: ATBC 100, maximum number of CC = 1 Class B: ATBC 100, maximum number of CC = 2 Class C: 100 < ATBC 200, maximum number of CC = 2

CA configuration: This defines the combination of operating bands and CA bandwidth class, for examples of Rel.10 and Rel.11 configurations, see the next slide

CA configuration examples (FDD)

Type of CA CA configuration

Max bandwidth Max number of CCs

Intra-band, contiguous (*)

CA_1C 40MHz 2

Intra-band, contiguous (**)

CA_7C 40MHz 2

Inter-band (*) CA_1A_5A 20MHz 1+1 Inter-band (**) CA_3A_5A 30MHz 1+1 Intra-band, non- contiguous (**)

CA_25A_25A 20MHz 1+1

(*) Rel.10; (**) Rel.11

Practical limits, and uplink and downlink configurations (Rel. 10-11)

The maximum aggregated bandwidth in Rel.11 is still only 40 MHz and the maximum number of CC is 2 There are more configurations in Rel.11 than we have given in the

previous slide. Yet, at maximum 40MHz and up to 2 CCs are allowed More configurations will be introduced in later LTE releases.

For both Rel.10 and Rel.11 an uplink CC should have the same bandwidth as the corresponding downlink CC.

For inter-band CA only one uplink CC is supported. That is, uplink CA is not defined for inter-band CA.

Recall: some E-UTRA frequency bands

Band Uplink (MHz) Downlink (MHz) Region

1 1920 - 1980 2110 - 2170 Europe, Asia

3 1710 - 1785 1805 - 1880 Europe, Asia, Americas

5 824 - 849 869 - 894 Americas, Korea,

7 2500 - 2570 2620 - 2690 Europe, Asia, Canada, Korea

8 880 - 915 925 - 960 Europe, Japan, Latin America

13 777 - 787 746 - 756 Americas, Verizon

http://www.etsi.org/deliver/etsi_ts/136100_136199/136104/11.02.00_60/ts_136104v110200p.pdf

For more, see:

CA deployment options

The coverage areas of component carriers can be different due to Large frequency separation between CCs Transmission power is not the same for all CCs Antenna directions are not the same for all CCs

2/19/2010 Word template user guide

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eNodeB eNodeB eNodeB RRH

Here Remote Radio Head (RRH) is connected to eNodeB

CA deployment options

Interesting CA scenario occurs when operator uses e.g. 2GHz and 800MHz bands for LTE Example: configuration CA_1A_5A

On the other hand, 3.5GHz will become available for mobile systems and can be used in hot spots.

Load balancing between CCs will not be trivial due to traffic variations within coverage areas of different CCs

Local RRH extensions are also becoming increasingly important. CA is then well possible if the same eNodeB is controlling main antenna unit and RRH

1.3 Primary and secondary Component Carriers

Primary and secondary CC

When UE first establishes RRC connection with eNodeB, only one CC is attached for downlink and uplink directions. Corresponding CCs are called as primary CCs (PCCs) for both downlink and uplink, and the related cell is the primary serving cell (PCell).

Based on the traffic load and QoS requirements, UE can be attached with additional one (or more) CC, called as secondary CC (SCC) which correspond to the secondary serving cell (SCell).

The use of downlink/uplink SCC is decided by the eNodeB. The PCC/SCC configuration is UE-specific and can be different for different UEs served by the same eNodeB.

Primary and secondary CC

Frequency

Band 1 Band 2

PCC PCC

SCC

SCC

CC1 CC2 CC3

PCC

Primary and secondary CC

The PCC serves as an anchor CC for the user and it is used for basic connectivity functionalities

The SCCs carry only dedicated signaling information PDSCH (physical DL shared channel), PUSCH (physical UL shared

channel), and PDCCH (physical DL control channel) Since user connection greatly depends on PCC, it should be robust

in both downlink and uplink PCC should be selected such that it provides ubiquitous coverage and/or

best overall signal quality When UE is moving within the eNodeB service area the PCC may

be changed CC with best signal quality Load balancing carried out between CCs

1.4 Radio Resource Management principles for Carrier Aggregation

Radio Resource Management in CA

Admission control is performed as in LTE by the eNodeB before establishing new radio bearer(s)

Based on user QoS requirements and traffic load, the eNodeB assign a set of CCs for user and physical layer scheduling is carried out over multiple users on each CC. Cross-carrier scheduling is also possible

To keep CA compatible with Rel.8/9 independent layer 1 transmissions are executed in CCs

Link adaptation and HARQ are carried out per CC

Radio Resource Management in CA Admission control L3 operations Cross-carrier

scheduling

Packet scheduling

LA, HARQ

L1 (PHY)

CC2

Packet scheduling

LA, HARQ

L1 (PHY)

CC1

Radio Resource Management in CA

Each component carrier has its own transmission parameters (e.g., TX power, modulation and coding schemes, and MIMO configuration) in the physical layer

Each component carrier has an independent hybrid automatic repeat request (HARQ) entity in the MAC layer.

In cross-carrier scheduling PDCCH is transmitted from a particular CC and may contain the scheduling information on other CCs as well as its own CC.

Thus, downlink of PCC can be used to schedule downlink and uplink resources on the SCCs. This method can be useful in interference and load management of HetNet

The downlink SCCs can be dynamically activated and deactivated => power consumption optimization in UE

1.5 Carrier Aggregation RLB example

RLB example on different component carrier coverage areas Assume the link budget parameters below, 10MHz band, 800MHz/2GHz

component carriers, 35 meter base station antenna height and 1.5 meter UE height. Compute the coverage in case of large city for 2Mbps service when eNodeB

allocates 4 PRBs for the user (12 users/cell served simultaneously).

eNodeB

Coverage area for 800MHz carrier

Coverage area for 2GHz carrier

Radio Communication Systems II, Exercise 3, 2014 Problem 1. LTE downlink RLB (excel in Noppa): Assume the following link budget parameters 2.1GHz carrier, 25 meter base station antenna height and 1.5 meter UE height:

Parameter Value BS TX power 40W BS antenna gain 18dBi BS cable loss 2dB UE noise figure 7dB Interference margin 4dB RX antenna gain 0dBi RX body loss 0dB Control channel overhead 1dB Indoor penetration loss 20dB Shadow fading margin 7dB BS antenna configuration 2x2/4x4 MIMO

(a) Compute the coverage (large city, rural area) for 5Mbps service when BS allocates 10 PRBs for the user. What happens to the service coverage if BS can allocate all available 48 PRBs for this user (target rate being the same 5 Mbps)?

(b) Increase the user rate 10Mbps and compute solve a) (large city, rural area)? (c) In remote rural area LTE is used on 800MHz to provide mobile broadband for single

houses (e.g. farms). If user is applying simple directive antenna with 5dBi gain on house rooftop (5 meters height) and LTE receiver is connected to WiFi (through cable) that provides indoor connectivity, what is then maximum cell range for 5Mbps service if user can apply 10 PRBs? What happens if rate requirement is increased to 10Mbps?

Assess in all cases a)- c) the impact of MIMO. Does 4x4 MIMO provide significant gain over 2x2 MIMO? Problem 2. LTE downlink RLB. In problem 1 a): write down all computations that excel does when computing allowed propagation loss. Make sure that you understand all phases in link budget calculations of problem 1. Problem 3. In Figure 1 the LTE link spectral efficiency is given as a function of Signal to Interference and Noise ratio. The curve with crosses (x) is related to 2x2 MIMO transmission while curve marked by circles (o) is related to 4x4 MIMO transmission. The LTE bandwidths and number of resource blocks for different band options are given in Table below.

(a) Using Figure 1 define what is the maximum data rate (in bits/s) for 2x2 and 4x4 MIMO in 3MHz and 10MHz deployments.

(b) User with 5 RBs and 4x4 MIMO is served. What is the minimum required SINR when user data rate should be at least 10Mbit/s?

(c) Scheduler allocates for the user 3 RBs. What is the data rate of the user with 4x4 MIMO if SINR=12.5dB. How much rate is decreased if 2x2 MIMO is used instead of 4x4 MIMO?

RLB example on different component carrier coverage areas 2GHz component carrier:

Indoor user maximum distance from eNodeB = 300 meters Outdoor user maximum distance from eNodeB = 1130 meters

800MHz component carrier: Indoor user maximum distance from eNodeB = 730 meters

Remarks: If network coverage planning has been done assuming 800MHz carrier and

indoor users, then 2GHz CC outdoor coverage is even larger than 800MHz CC coverage.

Thus, indoor users close to eNodeB and outdoor users in the whole cell can be scheduled to 2GHz CC

RLB example on different component carrier coverage areas

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Indoor coverage area for 800MHz carrier

Indoor coverage area for 2GHz carrier

Overlapping 800MHz indoor coverage and 2GHz outdoor coverage