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Carrier AggregationCarrier Aggregation

Pr. Sami Pr. Sami TabbaneTabbane

ITU ASP COE Training on« Wireless Broadband Roadmap Development”

11-14 September – Bangkok (Thailand)

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SummarySummary

I. Introduction : Trends in broadband wirelesssystems and Spectrum pressures

II. Carrier aggregation in LTE-A and othersimilar systems using carrier aggregation (e.g.,CDMA2000). Integration of carrier aggregationin the standards

III.Carrier aggregation and performanceIV.Cognitive radio: generalization of carrier

aggregation conceptV. Conclusions

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I. IntroductionI. Introduction

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State State of art of existing WB Systemof art of existing WB System

� ITU-T : Definition of the characteristics of the generation (2, 3,4, …), validation of proposed standards and allocation ofspectrum,

� 3GPP: European standardization body (“GSM” family),

� 3GPP2: North-American standardization body (“CDMA”family),

� IEEE : data networks standards (“802.xx” family),

� …

Standardization bodies

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Typical userdata rates

3G basic

HSPA

LTE

LTE-Advanced

100 kbps 1 Mbps 10 Mbps 100 Mbps

150-350 kbit/s

1.0 – 5 Mbit/s

5 – 60 Mbit/s

30 – 300 Mbit/s

State State of art of existing WB of art of existing WB SystemSystem

3GPP systems, 3GPP systems, Building on ReleasesBuilding on Releases

Release 10 LTE-Advanced meeting the requirements set by ITU’s IMT-Advanced project.

Also includes quad-carrier operation for HSPA+.

Release 99: Enhancements to GSM data (EDGE). Majority of deployments today are based on Release 99. Provides support for GSM/EDGE/GPRS/WCDMA radio-access networks.

Release 4: Multimedia messaging support. First steps toward using IP transport in the core network.

Release 5: HSDPA. First phase of Internet Protocol Multimedia Subsystem (IMS). Full ability to use IP-based transport instead of just Asynchronous Transfer Mode (ATM) in the core network.

Release 6: HSUPA. Enhanced multimedia support through Multimedia Broadcast/Multicast Services (MBMS). Performance specifications for advanced receivers. Wireless Local Area Network (WLAN) integration option. IMS enhancements. Initial VoIP capability.

Release 7: Evolved EDGE. Specifies HSPA+, higher order modulation and MIMO. Performance enhancements, improved spectral efficiency, increased capacity, and better resistance to interference. Continuous Packet Connectivity (CPC) enables efficient “always-on” service and enhanced uplink UL VoIP capacity, as well as reductions in call set-up delay for Push-to-Talk Over Cellular (PoC). Radio enhancements to HSPA include 64 Quadrature Amplitude Modulation (QAM) in the downlink DL and 16 QAM in the uplink. Also includes optimization of MBMS capabilities through the multicast/broadcast, single-frequency network (MBSFN) function.

Release 8: HSPA Evolution, simultaneous use of MIMO and 64 QAM. Includes dual-carrier HSPA (DC-HSPA) wherein two WCDMA radio channels can be combined for a doubling of throughput performance. Specifies OFDMA-based 3GPP LTE.

Defines EPC.

Release 9: HSPA and LTE enhancements including HSPA dual-carrier operation in combination with MIMO, EPC enhancements, femtocell support, support for regulatory features such as emergency user-equipment positioning and Commercial Mobile Alert System (CMAS), and evolution of IMS architecture.

Text adapted from 3G Americas White Paper, September 2010

Release 11Interworking - 3GPP EPS and fixed BB accesses, M2M, Non voice emergency communications, 8 carrier HSDPA, Uplink MIMO study

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Releases Releases and bitrates and bitrates expectationsexpectations

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Peak data rates Peak data rates in LTE and LTEin LTE and LTE--AA

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TheoreticalTheoretical spectrum spectrum efficienciesefficiencies

LTE is the most spectral efficient wireless technology but it cannotbe expected that early LTE deployments achieve this theoreticalspectral efficiency.

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Main LTE data rates Main LTE data rates improvement techniques:improvement techniques:-- Link adaptationLink adaptation-- MIMO and MIMO and beamformingbeamforming-- Fast schedulingFast scheduling-- Hybrid ARQHybrid ARQ-- ……

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LTE physical layerLTE physical layer

� Flexible bandwidth (with resolution of 180 kHz)– Possibility to deploy in bandwidth of <5 MHz to

20 MHz

� UL: SC-FDMA with a dynamic bandwidth (pre-coded OFDM)– PAPR � Better spectrum efficiency– Reduced UL interference (allows intra-cell orthogonality)

� DL: adaptive OFDM

– Scheduling channel and link adaptation dependent in the time and frequency domain

� Multiple antennas, RBS and terminal– MIMO, antennas lobes, TX- and RX diversity, interference rejection – High bitrates and higher capacity

TXTX RXRX

frequency

frequency

� Harmonised FDD and TDD concept– FDD and TDD maximum spectrum sharing

� Maximum UE capacity: BW = 20 MHz

10 15 20 MHz< 5 5

fDL

fUL

FDDFDD--onlyonlyfDL

fUL

HalfHalf--duplex FDDduplex FDDfDL/UL

TDDTDD--onlyonly

∆f=15kHz

180 kHz

User #2 scheduledUser #1 scheduled

User #3 scheduled

Link Link adaptationadaptation

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Example of link adaptationExample of link adaptation

MIMO and MIMO and BeamformingBeamforming

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Fast schedulingFast scheduling

Scheduling depending on the channel

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Hybrid ARQHybrid ARQPrinciple: Reuse of the errored frames for the decoding of

the retransmissions.

Drawback: Requires a large buffer.Loss of the frame #2 => retransmission request

Link layer

Physicallayer

Time

2error

Storage in the HARQ buffer

+ Combines the errored frame with

the retransmitted one

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II. Carrier aggregation II. Carrier aggregation in LTEin LTE --A and other A and other

systemssystems

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LTELTE--A improvements (1)A improvements (1)

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LTELTE--A improvements A improvements (2)(2)

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Impacts of various techniques in Impacts of various techniques in improving the data ratesimproving the data rates

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Carrier Carrier aggregationaggregation in LTEin LTERelease-10 carrier aggregation supports the following features:

� Peak data rates of 1 Gbps on downlink and 500 Mbps on uplink.

� Up to five carriers can be aggregated, each carrier is called a “component carrier”.

� Each component carrier can have any of the bandwidths supported in LTE Rel-8 (1.4, 3, 5, 10, 15 and 20 MHz). As a result, LTE carrier aggregation can support operation on transmission bandwidths of up to 100 MHz by aggregating five 20 MHz carriers.

� Each component carrier is fully backward compatible to Release-8/9. This backward compatibility to Release 8/9 allows the technologies developed for LTE Release-8/9 to be fully reused in Release-10. It also allows the coexistence of Release 8 and 9 UEs together with Release-10

UEs, which is very important for seamless system transition from Release 8 and 9 to Release 10.

� A carrier aggregation capable UE can simultaneously receive and transmit in one or multiple component carriers.

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Carrier aggregation in LTECarrier aggregation in LTE

Carrier Aggregation (CA): multiple component

carriers are aggregated and jointly used for

transmission to/from a single terminal. There are up

to five component carriers, possibly each of

different bandwidth, which can be aggregated,

allowing for transmission bandwidth up to 100 MHz

backwards compatibility where, each component

carrier (CC) uses the release-8 structure.

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Key Features in LTE Release 10Key Features in LTE Release 10

Support of Wider Bandwidth (Carrier Aggregation)

Advanced MIMO techniques• Extension to up to 8-layer transmission in downlink• Introduction of single-user MIMO up to 4-layer transmission

in uplink

Heterogeneous network and eICIC (enhanced Inter-Cell Interference Coordination)

• Interference coordination for overlaid deployment of cells with different Tx power

� Improvement of cell-edge throughput and coverage

Relay

Coordinated Multi-Point transmission and reception (CoMP)

100 MHz

f

CC

LTELTE--A features for increased A features for increased bitratesbitrates

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Carrier aggregation benefitsCarrier aggregation benefits

� Maximize the total peak data rate and throughputperformance by combining peak capacities and throughput

performance available at different frequencies

� Provide a higher and more consistent quality ofserviceby load-balancing across frequencies and systems.

� Mitigate the relative inefficiencies that may be

inherent in wireless deployments in non-contiguous or

narrow (5 MHz or less) channel bandwidths, often spread

across different spectrum bands.25

Carrier aggregation in HSDPACarrier aggregation in HSDPA

8C-HSDPA is a further extension of the multicarrier operation witheight carriers. Similar to the 4 carrier feature, in 8C-HSDPA thetransmissions are independent. The carriers do not need to beadjacent. The activation/deactivation of the secondary carriers isdone by the serving NodeB through physical layer signaling. Theuplink signaling is carried over a single carrier. 26

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HSPA + LTE HSPA + LTE Carrier Carrier AggregationAggregationSame mechanisms as the intra-RAT carrier aggregation schemes. It bring similar

data rate gains:

� Data rates of carrier aggregation UEs boosted by utilizing unused resources from overlapping cell(s) operating on different carrier(s)

� Data rates of all UEs improved by fast (TTI level) load balancing

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III. Carrier aggregation III. Carrier aggregation performanceperformance

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Carrier aggregation impact on Carrier aggregation impact on throughputsthroughputs

Improves average cell throughput both in uplink and downlink due to more efficient utilization of radio resource by statistical multiplexing 29

InterInter--band Carrier Aggregation enables to benefit from different band Carrier Aggregation enables to benefit from different propagation characteristic of propagation characteristic of different frequencydifferent frequency bandsbands

Carriers at different frequency bands have different propagation losses and different interfering systems. Far-off UE are better served with a low frequency carrier and near cell center UE with a high frequency carrier.

Inter-band Carrier Aggregation provides more flexibility to utilize fragmented spectrum allocations.30

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Average downlink data rate before and after refarming of one HSPA carrier (assuming low-to-medium system loading, 10MHz

LTE and 2x5MHz HSPA before refarming)

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UE capabilities and carrier UE capabilities and carrier aggregationaggregation

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Different types of carrier Different types of carrier aggregation in LTE (1)aggregation in LTE (1)

ExampleExample of carrier aggregation of carrier aggregation in different frequency in different frequency bandsbands

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ComponantComponant carriers after carrier carriers after carrier aggregationaggregation

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Symmetric/Asymmetric carrier Symmetric/Asymmetric carrier aggregation in aggregation in LTELTE

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A. Intra-band aggregation with frequency-contiguous component carriers

Contiguous bandwidth wider than 20 MHz.

B. Intra-band aggregation with non-contiguous component carriers

Multiple CCs belonging to the same band. Countries where spectrum allocation is non-contiguous within a single band.

C. Inter-band aggregation with non-contiguous component carriers

Carriers in different operating bands are aggregated. Inter modulation and cross-modulation within the UE device when multiple transmitter and receiver chains are operated simultaneously.37

Intra/InterIntra/Inter--band carrier band carrier aggregation in aggregation in LTE (1)LTE (1)

Spectrum Aggregation Scenarios for Spectrum Aggregation Scenarios for FDDFDD

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Intra/InterIntra/Inter--band carrier band carrier aggregation in LTE (2)aggregation in LTE (2)

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IntraIntra--Band Carrier Aggregation RF Band Carrier Aggregation RF parameters with 2 aggregated parameters with 2 aggregated carrierscarriers

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Carrier AggregationBandwidth Class

Aggregated TransmissionBW Configuration

A ≤100

B ≤100

C 100 - 200

The 6 LTE carrier aggregation bandwidth The 6 LTE carrier aggregation bandwidth classesclasses

N.B.: classes D, E, & F are in the study phase.

Downlink Multiple Access Scheme with Downlink Multiple Access Scheme with CACA

• Downlink OFDMA with component carrier (CC) based structure• One transport block is mapped within one CC

• Parallel-type transmission for multi-CC transmission

– Cross-carrier scheduling is possible–DL control channels (such as PDCCH, PCFICH, and PHICH) are updated to support cross-carrier scheduling.

– Add a Carrier Indicator Field (CIF) to DCI.42

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Advantages of CAAdvantages of CA

�Lot of permutations and combinations, some of them are a bit more difficult to implement due to interference problems caused (intermodulation products of transmitted signals on differentfrequency bands).

�Only intraband carrier aggregation is supported in uplink in LTE Release 10 (higher range of band combinations will be supported in later releases).

�Carrier aggregation provides almost as high spectrum efficiency and peak rates as single wideband allocation.

�In heterogeneous deployment scenarios, the performance can be better since flexible frequency reuse can be arranged between local area nodes to provide better inter-cell interference coordination.

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CA between operatorsCA between operators

�The system bandwidth will increase substantially,

up to 80 MHz

�For two cooperating operators with 2*20 MHz

each. The average data rates can reach 80 or 160

Mbps, and the peak data rates can be up to 400 or

800 Mbps.

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Drawbacks of CA (1)Drawbacks of CA (1)Loss in throughput: by the vulnerability due to channel aggregation or bonding in LTE-A and HSPA+ networks.

Channel aggregation is susceptible to about 70% loss of throughput in LTE networks and about 11-15% in HSPA+ networks compared to systems with no aggregation or bonding.

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Drawbacks of CA (2)Drawbacks of CA (2)

• Interference coordination,

• UE compatibility (frequency bands, bandwidths, …),

• Radio planning constraints,

• …

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IV. Cognitive radio: IV. Cognitive radio: generalization of the generalization of the carrier aggregation carrier aggregation

conceptconcept

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The origin: Apparent The origin: Apparent Spectrum ScarcitySpectrum Scarcity

Spectrum measurement across the 900 kHz –1 GHz band (Lawrence, KS, USA)

Spectrum Holes

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RF Spectrum OccupancyRF Spectrum Occupancy

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Spectrum measurement across the 928 – 948 MHz band (Worcester, MA, USA)

The Idea: Dynamic The Idea: Dynamic Spectrum Spectrum AccessAccess

Fill with secondaryusers

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White Space ConceptWhite Space Concept

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Cognitive Radio: DefinitionCognitive Radio: Definition

“Cognitive radio is an intelligent wireless communication systemthat is aware of its surrounding environment (i.e., outside world),and uses the methodology of understanding-by-building to learnfrom the environment and adapt its internal states to statisticalvariations in the incoming RF stimuli by making correspondingchanges in certain operating parameters (e.g., transmit-power,carrier-frequency, and modulation strategy) in real-time, with twoprimary objectives in mind:

• highly reliable communications whenever and wherever needed;

• efficient utilization of the radio spectrum.”

S. Haykin, “Cognitive Radio: Brain-Empowered Wireless Communications”, IEEE J-SAC, Feb. 2005.

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Cognitive RadioCognitive Radio

Cognitive radio technology is expected to improve spectrum access through:

� Increased spectrum efficiency of licensed spectrum users

�Secondary markets by allowing licensees to lease their spectrum access e.g. by machine-controlled negotiation between systems

�Automated frequency coordination between licensees

�Opportunistic spectrum use by unlicensed devices while protecting incumbents from harmful interference

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TerminologyTerminology

• Primary User (PU):

– Licensed user

– Has exclusive rights for the spectrum

• Secondary User (SU):

– Unlicensed user

– Opportunistically utilizes the white spaces

– Has to vacate the spectrum band as soon as a PU appears

– Also called cognitive user

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Frequency

T

I

M

E

Spectral Adaptation Waveforms

Example of OFDM Example of OFDM Carriers Selected for Use That Fall Carriers Selected for Use That Fall into Available Spectruminto Available Spectrum

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ConclusionsConclusions

� To achieve up to 1 Gbps peak data rate in the downlink

and 500 Mbps in the uplink in future IMT-Advanced

mobile systems, Carrier Aggregation (CA) technology is

introduced by the 3GPP to support very-high-data rate

transmissions over wide frequency bandwidths (e.g., up

to 100 MHz) in its new LTE-Advanced standards.

� In CA, communication is achieved through the

simultaneous use of multiple LTE carriers called

Component Carriers (CCs) enabling broadband

transmission exceeding 20 MHz.