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Aalborg Universitet

Status på LTE-A

Sørensen, Troels Bundgaard

Publication date:2012

Document VersionAccepteret manuscript, peer-review version

Link to publication from Aalborg University

Citation for published version (APA):Sørensen, T. B. (2012). Status på LTE-A: Standardisering og teknologi. Poster session præsenteret ved Statusog perspektiv for næste generation Mobilt bredbånd i Danmark, København, Danmark.

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1 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012

Status på LTE-AStandardisering og teknologi

Præsenteret af Troels B. SørensenSektionen for Radio Access Teknologi (RATE), Aalborg UniversitetIDA-TTS Konference, 4. december, 2012

2 © Aalborg University/RATE IDA-TTS konference/ Troels B. Sørensen / 4. december 2012Matti Kiiski, 1 July 2011


Standardization

ITU-R – International Telecommunication Union - Radiocommunication (sector)IMT-A – International Mobile Telecommunications - AdvancedE-UTRAN – Evolved UMTS Terrestrial Radio Access NetworkUMTS – Universal Mobile Telecommunications System3GPP – 3rd Generation Partnership ProgramLTE – Long Term EvolutioneNB – evolved Node BUE – User Equipment


Requirements

• The 3GPP LTE evolution to meet/exceed the ITU-R IMT-Advanced capabilities of a 1Gbps (4G) system– Peak data rates of 100 Mbit/s for high and 1 Gbit/s for low mobility– Peak spectral efficiencies 15bps/Hz downlink (4×4 MIMO) and 7.5bps/Hz uplink

(2×4 MIMO)– Bandwidth scalability up to 40MHz, and preferably to 100MHz– User plane latency 10ms and 100ms for control (idle to active)

• 3GPP set its own requirements for LTE-Advanced as detailed in 3GPP TR 36.913, including– Increased spectral efficiencies (improved efficiency over LTE)

Average targets increased 30% for downlink and 40% for uplink Peak extended to 8×8 MIMO downlink and 4×4 MIMO uplink

– Meeting 3GPP operator requirements for the evolution of E-UTRASelf-Organizing Networks (SON)

– Backwards compatibility requirementsA Release 8 E-UTRA terminal can work in an Advanced E-UTRAN, An Advanced E-UTRA terminal can work in an Release 8 E-UTRAN


Technology Components

Carrier Aggregation

MIMO

Cooperative Systems

Relaying

8x 4x

Backward compatible

to LTE

Mobility

Heterogeneous Networks

1st LTE field trialBerlin, 11/2007

Smooth Migrationto LTE-A

Key ingredients

Carrier1 Carrier2 Carrier3 … Carrier5

up to 100 MHz

These fulfill the ITU requirements for 3-sector macro

LTE standardization is not driven only by

IMT-Advanced!


Standardization – 3GPP Releases

2008 2009 2010 2011

LTE-AStudy Items

Rel. 10

LTE-A

LTE-AWork Items

“The 18 months cycle” for releases -

and market (terminal) introduction

First LTE-A release …

PAST

2012 2013 2014 2015

Rel. 11

LTE-A

?Rel. 12… and the

next almost here

NOW


Standardisation - Specifications

• The core of the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) specifications relates to the 36 series of the 3GPP specifications– http://www.3gpp.org/specification-numbering (overview of the 3GPP

specification numbering)

Specifications and responsible Radio

Access Network (RAN) Working Group

After “LTE for UMTS”, Wiley 2011

LTE and LTE-A in Rel. 10 and beyond specifications

RF: 36.101 - 36.104, 36.133 (RAN4)

L2/L3: 36.321 – 36.323, 36.331, 36.304/306

(RAN2)

L1: 36.211 - 36.214(RAN1)

X2: 36.421 - 36.424(RAN3)

S1: 36.411 - 36.414(RAN3)

Packet coreAir interface

eNBS1

X2

UE


Technology ComponentsCA, MIMO, HetNet (eICIC), CoMP, Relays


Carrier Aggregation (CA)BW – BandwidthRRC – Radio Ressource Control (layer or signalling)PDCCH – Physical Downlink Control CHannelPUCCH – Physical Uplink Control CHannelCQI – Channel Quality IndicatorFDD – Frequency Division DuplexDL – DownlinkUL – UplinkCC – Component CarrierPCell/SCell – Primary and Secondary CellCRS – Common Reference SignalPSS/SSS – Primary and Secondary Synchronization SignalOFDM – Orthogonal Frequency Division Multiplexing

CCE – Common Control ElementBCCH – Broadcast Control CHannelRRC – Radio Ressource Control (signalling)CQI – Channel Quality IndicatorNACK/ACK – Negative AcknowledgeCSI – Channel State InformationPRB – Physical Resource Block


Carrier Aggregation (CA)

• High peak data rates achieved even with fragmented spectrum (important practical aspect)

• Backwards compatibility requirements with Release 8 LTE is achieved with carrier aggregation by combining up to N = 5 Release 8 component carriers to form N x LTE bandwidth, for example 5 x 20 MHz = 100 MHz

• LTE terminals receive/transmit on one component carrier, whereas LTE-Advanced terminals may receive/transmit on multiple component carriers simultaneously

Both contiguous and non-contiguous CA is supported offering improved spectrum flexibility (e.g. for

refarming).

Primary and Secondary Cells

(Component Carriers - CC)


CA Band Combinations

• Initial focus is on CA for two band combinations, specific to different regions of the world– Radio frequency aspects are being handled per case and in a release independent

manner

• Current RF specification work has beenprioritized to focus on downlink CA– CA for uplink is more complicated and

will be standardized based on the DL CA combinations

SpuriousHarmonicsBroadband noise

Band 20: 791 – 821 MHz (DL) | 832 – 862 MHz (UL) Band 7: 2500 – 2570 MHz (UL) | 2620 – 2690 MHz (DL)

Band 3 + 7(FDD)

Band 20 + 7(FDD)

Band 3: 1710 – 1785 MHz (UL) | 1805 – 1880 MHz (DL) Band 7: 2500 – 2570 MHz (UL) | 2620 – 2690 MHz (DL)

Need for (maximum) power reduction of

4-6dB


CA Gain Mechanisms

• Multi-carrier scheduling allows for: – more bandwidth per user (peak data rate) and better use of high frequency bands

(coverage)– load balancing/ressource sharing and frequency domain scheduling across carriers

Segm.ARQ etc

Multiplexing UE1

Segm.ARQ etc...

Scheduling / Priority Handling

Logical Channels

Transport Channels

MAC

RLC Segm.ARQ etc

Segm.ARQ etc

PDCPROHC ROHC ROHC ROHC

Radio Bearers

Security Security Security Security

...

HARQ HARQ...

Multiplexing UEn

HARQ HARQ...

CC1 CCx... CC1 CCy...

Independent HARQ per CC. Thus, HARQ retransmissions

shall be send on the same CC as the corresponding original

transmission

There is one PDCP and RLC per Radio Bearer. Not visible from

RLC on how many CCs the PHY layer transmission is conducted.

Separate transport channel per CC

Dynamic Layer-2 packet scheduling accross multiple CCs

supported


CA Signalling

• Each CC provides reference (CRS) and synchronisation signals (PSS/SSS), as well as system broadcast information (BCCH) specific to that carrier– only PCell however carries radio ressource control (RRC) signalling - for bearer setup, CA

configuration, mobility measurements, handover, …– individual SCells can be activated

/deactived with MAC controlelement to save terminal power – within 7ms

• Added capacity in control channels for multi-carrier to support more CQI requests, ACK/NACK and CSI reporting, power headroom signalling .. and somesimplifications to reduce terminal complexity at the same time– reduced need for DPCCH decoding on SCells (e.g. CCE blind decoding on PCell only),

control signalling in uplink PCell PUCCH only– Cross-carrier scheduling capability of special importance to heterogeneous network

operation

TTI with 2 slots of 0.5 ms (14 OFDM symbols)

Freq

uenc

y

Time

PRB

OFDM SymbolPDCCH


Multiple Input Multiple Output (MIMO)SISO – Single Input Single Output (antenna system) MU-MIMO – Multi-User MIMOSU-MIMO – SIngle User MIMOPMI – Precoding Matrix IndicatorDM-RS – Demodulation Reference SignalCSI-RS – Channel State Information – Reference SignalURS – UE specific Reference SignalOCC – Orthogonal Cover CodesSRS – Sounding Reference SignalCM – Cubic MetricSC – Single CarrierCQI – Channel Quality Indicator

Precoding – ”Antennevægtning af TX-antenner”


MIMO

• The targeted data rates of LTE-A can only be achieved by using advanced Multiple Input Multiple Output (MIMO) antenna techniques

• Primarily an evolution of LTE MIMO ...– Transmit Diversity/Beamforming (Open/Closed Loop)– Spatial Multiplexing (Open Loop)– Precoded Spatial Multiplexing (Closed Loop)

• .. except for – Increased MIMO constellations– Uplink Single-User MIMO (SU-MIMO)– Flexible Multi-User Scheduling in both downlink and uplink

SISO2x2 MIMO4x4 MIMO8x8 MIMO

SISO2x2 MIMO4x4 MIMO

Downlink Uplink

Tx

1

2

NT

1

2

NR

Rx

feedback

DiversitygainCoherent

gainMultiplexing

gain


Downlink MIMO

eNB

CQI, PMI

MIMO UE4

UE3

MIMO UE2

MIMO UE1

Data Stream 1

Data Stream 2

Data Stream 1

Data Stream 2

Data

MU-MIMOTransmit Diversity

/Beamforming

SU-MIMO

CQI, PMI, RIDynamic

switching based onoptimised feedback

CQI, PMI, RI ”Double codebook”for 8 TX antennas

”New” UE specific reference signal (URS) for demodulation:

Includes precoding information for flexibleMU-MIMO operation

(pairing per ressource)

New reference signals ”replacing”Common Reference Signal (CRS):

Sparse CSI-RS for feedback generation reduces overhead


Uplink MIMO

eNB

UE3

UE2

UE1

Data Stream 1

Data Stream 2

DataVirtual (MU)-MIMO Transmit diversity

MIMO UE4Data Stream 1

Data Stream 2

SU-MIMOWideband (Closed

Loop) Precoding whichis Cubic Metric (CM)

preserving

Aperiodic and dynamic SRS reference signal transmisson:

Enhances the use of SRS ressources

New Orthogonal Cover Code (OCC) on top of demodulation reference signal (DM-RS):Allows separation of partially overlapping

transmissions for flexible MU-MIMO operation


Reference signals (DL)

OFDM symbols

Sub

carri

ers

”The Devil is in the details!”

Sparse CSI-RS, sent only when in fact needed (overlapped with data transmissions) to reduce overhead

for large MIMO constellationsSupport for 2, 4 and 8 TX antennas

URS (DM-RS) sent withprecoding, hence no need to signal precoder separately

Allows decoupling in spatial and frequency

domain scheduling

In uplink, the same scheduling flexibility is introduced using OCC


Performance

QAM – Quadrature Amplitude ModulationUL/DL – Uplink and Downlink


UE Categories• In addition to the existing 5 categories in rel. 8 (LTE), three new

terminal categories added in rel. 10 specifications

• Peak data rates can be achieved in different combinations from CA and MIMO capabilities

Class 4 --- Class 6 Class 7 Class 8150/50 Mbps 300/50 Mbps 300/100 Mbps 3000/1500

MbpsPeak rate DL/UL

64QAMModulation DL 64QAM 64QAM 64QAM

16QAMModulation UL 64QAM 16QAM 16QAM

2x2MIMO DL 8x8 with CA2x2 with CA*4x4 without CA

2x2 with CA*4x4 without CA

NoMIMO UL 4x4 with CANo 2x2

Downlink 4x4 MIMO: 15bps/Hz

Uplink 2x2, MIMO (64QAM): 7.5bps/HzCell edge

efficiency is about 1% of

peak!

* Carrier aggregation of two 20MHz carriers


Cell Performance• From simulations, average LTE-A cell spectral efficiencies exceed ITU

requirements

• Much of the gain can be achieved already with LTE rel. 8 (e.g. Multi-User MIMO), but additional MIMO capability and flexibility in scheduling gives additional gain for LTE-A rel. 10

– Downlink: UE specific reference signals (URS, or DM-RS), dynamic switching SU/MU-MIMO and optimised double codebook feedback for 8 TX antennas

– Uplink: SU-MIMO operation, orthogonal cover codes on DM-RS, dynamic aperiodic SRS transmission

2.6bps/Hz

2x2 MIMO

3.4bps/Hz

4x2 MIMO

4.7bps/Hz

4x4 MIMO1.4

bps/Hz1x2 MIMO

2.3bps/Hz

2x4 MIMO

DownlinkUplink

“LTE-Advanced; 3GPP Solution for IMT-Advanced", John Wiley, 2012


LTE-A Capability

LTE 50MHz FDD6GB/sub/month

LTE-A 50MHz FDD10GB/sub/month

LTE-A 50MHz FDDHetNet

54GB/sub/month

Heterogeneous Networks with small and large cells are essential to cell-edge improvements! – secondarily CoMP

LTE-A 50MHz FDDNetwork upgrade15GB/sub/month

LTE-A 100MHz FDDHetNet

107GB/sub/month

?

“LTE-Advanced; 3GPP Solution for IMT-Advanced", John Wiley, 2012


Heterogeneous Networks (HetNet)

ABS – Almost Blank SubframeHeNB – Home eNBCSG = Closed Subscriber GroupEIRP = Equivalent Isotropic Radiated PowerHeNB = Home base stationRE = Range ExtensioneICIC = Enhanced ICICHII = High Interference IndicationICIC = Inter-Cell Interference CoordinationOI = Overload IndicationRNTP = Relative Narrow band Transmit PowerSON = Self Optimizing Network


The Combined Benefit of Wide & Local Area

Macro

Micro

Pico, Femto

Share will grow in future• 10 – 100 m, • < 500 mW

Share of sites growing• 100 – 300 m • 1 – 5 W

Majority of cell sites today• > 300 m • > 5 W output power

License exempt growing & Secondary services emerging• 10-100 m• < 100 mW Access

Points

Wide Area sites

Medium area sites

Local area

Local area

Local area

Local area

WLAN

WLANWLAN

Medium area sites

Local area

WLAN

WLAN

Benefits of Multi-Layer Deployment• Coverage improvement from local area cells

in edge or shadowed regions• Capacity increase from more transmission

points in a given area

Tradeoffs involved with Multi-Layer• Co-channel deployment needs no additional

spectrum but creates interference between the layers and within the same layer >> this interference needs to be controlled for QoS


HetNet Co-Channel Interference

Pico eNB:Tx power: 30 dBmAntenna gain: 5 dBiEIRP: 35 dBm

Macro eNB:Tx power: 46 dBmAntenna gain: 14 dBiEIRP: 60 dBm

Macro eNB

CSG HeNB:Tx power: 20 dBmAntenna gain: 0 dBiEIRP: 20 dBm

Dominancearea of HeNB

Coverage area of pico without RE

Extendedcoverage area of

pico with RE

Coverage area of macro


LTE Multi-Cell Coordination via X2Cell ACell B

µ-cell B

µ-cell A1

No X2 betweenmacro and

HeNBs(rel.10 includes

X2 betweenHeNBs for some

cases)• Each 3GPP releases has added few new features:

– Release 8Mobility Management (Handover)ICIC (RNTP, HII, OI)SON Management

– Release 9SON enhancementsLoad balancingEnergy Saving

– Release 10TDM eICIC


TDM eICIC PrincipleAlmost blanksub-frame (ABS)Sub-frame withnormal transmission

Macro-layer

Pico-layer

HeNB-layer

Pico-nodes can schedule UEs withlarger RE, if not interfered from non-

allowed CSG HeNB(s)

Macro-eNBs and Pico-eNBs can schedulealso users that are close to non-allowed CSG

HeNB(s), but not pico-UEs with larger RE.

Pico-UEswith

largerRE,

close to CSG

HeNB(s) are

schedulable (as well as

pico-UEswithout

RE).


HetNet is ”hot”

Considered Small Cell Scenarios & ObjectivesOngoing LTE Rel-12 Study Item3GPP TR 36.932

Ongoing LTE Rel-12 Study Item3GPP TR 36.932

Cases with dedicated carrier deployment

Cases with dedicated carrier deployment

Macro-assisted and standalone small cell

solutions

Macro-assisted and standalone small cell

solutions

Enhanced mobility for dense small cell

deployments

Enhanced mobility for dense small cell

deployments

Efficient small cell SON

Efficient small cell SON

Study of PHY and Architecture

enhancements

Study of PHY and Architecture

enhancements

Exploiting new carrier type (NCT)

Exploiting new carrier type (NCT)

Spectrum:e.g. 3.5 GHz for small cells

Spectrum:e.g. 3.5 GHz for small cells

Energy efficient solution

Energy efficient solution

Rel. 12 WI on HetNetMobility improvements

for LTE (rel. 11 SI)

Rel. 12 WI on NCT

Rel. 12 WI on CarrierBased HetNet ICIC for

LTE (rel. 11 WI)

Rel. 12 SI onSmall Cell

Enhancements


Coordinated Multipoint (CoMP) Transmission and Reception

JP – Joint Processing


Cell A

CoMP Principle

Cell A (Anchor Cell for the CoMP Cooperative Set)

Cell BCell C

• A 3-cell CoMP Cooperative/Transmission Set in downlink

Inter-cell CoMP signaling


CoMP Techniques

• Categories of CoMP

– Joint Processing (JP):Data is available at each cell in CoMP cooperating set (CSI and scheduling info, AND data shared among cooperating cells)

Joint Transmission: Transmission from multiple points (part of or entire CoMPcooperating set) at a time Dynamic cell selection: Transmission from one point at a time (within CoMPcooperating set)• A single point is the transmission point at every subframe; this transmission point can change

dynamically within the CoMP cooperating set

– Coordinated Scheduling/Beamforming (CS/CB):Data is only available at serving cell and transmitted from that point (CSI and scheduling info shared among cooperating cells)

The user scheduling/beamforming decisions are made with coordination among cells corresponding to the CoMP cooperating set

Alike ICIC but faster and including spatial

domain


Relays


Relays

• Relay nodes with LTE backhaul – inband or outband– for coverage extension/cell edge performance improvement– backwards compatible with rel. 8

Macro eNodeB

Relay Nodes

Micro BTS

Backhaul linkRelay looks like an additional sector of

the macro

Access linkRelay looks like an eNB

seen from the UE

Full eNB functionality


Summary


Summary• Bandwidth has been extended in rel. 10 (LTE-A) up to 100MHz by using backwards

compatible carrier aggregation– Two carrier downlink CA combinations have been specified and more will come,

including uplink CA combinations • Support for Multiple Input Multiple Output (MIMO) antennas has been extended in

rel. 10– Uplink SU-MIMO up to 4 × 4 for increasing uplink peak spectral efficiency (up to

15bps/Hz) and enhance average cell spectral efficiency– Support of up to 8x8 MIMO in downlink to increase peak spectral efficiency (up to

30bps/Hz) and average cell spectral efficiency– “The Devil is in the details” of the reference signals, which has allowed

improvements especially to Multi-User MIMO• Multi-layer interference management for Heterogeneous Networks using time-

domain enhanced ICIC (eICIC)• CoMP techniques are still under investigation but included in rel. 11 for downlink and

improved for uplink over what is already possible with LTE rel. 8• Transparent relay nodes with wireless LTE backhaul were introduced in rel. 10,

primarily for cell edge improvements• With these techniques, the target of reaching a peak data rates of more than 1Gbit/s

and significant improved average cell spectral efficiency in both UL and DL are achieved


Literature

“LTE-Advanced; 3GPP Solution for IMT-Advanced", John Wiley, 1st

edition, September 2012, Edited by Harri Holma and Antti Toskala

“LTE for UMTS; Evolution to LTE-Advanced", John Wiley, 2nd

edition, March 2011, Edited by Harri Holma and Antti Toskala

“4G: LTE/LTE-Advanced for Mobile Broadband”, Academic Press, 2011, Edited by Erik Dahlman, Stefan Parkvall and Johan Skjold

“LTE-advanced and 4G wireless communications”, IEEE Communications Magazine, vol. 50, no. 2, February 2012

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