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42013 NTT DOCOMO, INC.Copies of articles may be reproduced only for per-sonal, noncommercial use, provided that the nameNTT DOCOMO Technical Journal, the name(s) ofthe author(s), the title and date of the article appearin the copies.

*1 HSPA: A specification for increasing packet-data rates in W-CDMA and a general termencompassing HSDPA (see *4), which increasesthe speed from the base station to the mobileterminal, and HSUPA (see *5), which increas-es the speed from the terminal to the base sta-tion.

Advanced Technologies in LTE/LTE-Advanced

Further Development of LTE/LTE-Advanced LTE Release 10/11 Standardization Trends

3GPP Release 11 LTE/LTE-Advanced IMT-Advanced

1. IntroductionThe 3rd Generation Partnership

Project (3GPP), which had previouslyformulated the specifications forWCDMA and High-Speed PacketAccess (HSPA)*1 as a third-generationmobile communications system, formu-lated a radio system called Long TermEvolution (LTE) in 2008 as 3GPPRelease 8 specifications (hereinafterreferred to as Rel. 8) in response togrowing market demands. It then wenton to formulate LTE-Advanced*2 as

3GPP Release 10 specifications (here-inafter referred to as Rel. 10) makingfurther enhancements to LTE. Never-theless, market demands for enhancedperformance continued to grow anddiversify, and in 2012, 3GPP formulat-ed Release 11 specifications (here-inafter referred to as Rel. 11) with theaim of extending the functions and rais-ing the performance of LTE-Advanced.In this article, we describe an overviewon how LTE specifications have pro-gressed over the years and summarizethe main function extensions in the

releases up to LTE Rel. 11.

2. Progression of3GPP Specifications

Since the formulation of W-CDMAspecifications as Release 99*3, manyfunctions have been added at 3GPP inthe form of new release specificationsin response to growing demands fromthe market. The progression of thesespecifications is shown in Figure 1.High-Speed Downlink Packet Access(HSDPA)*4 and High-Speed UplinkPacket Access (HSUPA)*5, which are


NTT DOCOMO Technical Journal Vol. 15 No. 2

Takehiro Nakamura0

Sadayuki Abeta0

Hideaki Takahashi0

Satoshi Nagata0

LTE was standardized at 3GPP, an international standardsorganization, as 3GPP Release 8 in 2008 with an eye toachieving dramatic improvements over the third-generationmobile communications system. This was followed by thestandardization of LTE-Advanced as Release 10 to achieveeven higher speeds and capacities in mobile communica-tions. At present, 3GPP is in the process of completingRelease 11 specifications and beginning the formulation ofRelease 12. This article describes an overview on the pro-gression of LTE and LTE-Advanced standardization andsummarizes the main function extensions in the abovereleases.

Radio Access Network Development Department

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LTE was standardized at 3GPP, an international standards organization, as 3GPP Release 8 in 2008 with an eye to achieving dramatic improvements over the third-generation mobile communications system. This was followed by the standardization of LTE-Advanced as Release 10 to achieve even higher speeds and capacities in mobile communications. At present, 3GPP is in the process of completing Release 11 specifications and beginning the formulation of Release 12. This article describes an overview on the progression of LTE and LTE-Advanced standardization and summarizes the main function extensions in the above releases.

5already in widespread use around theworld, are included in Release 5 andRelease 6, respectively. These 3GPPspecifications related to W-CDMA andHSDPA/HSUPA are contained in theInternational Mobile Telecommunica-tions-2000 (IMT-2000)*6 Recommenda-tion of the International Telecommuni-cation Union-Radiocommunication sec-tor (ITU-R)*7.

The LTE system was formulated at3GPP at the end of 2007 as Rel. 8 spec-ifications to provide a mobile commu-nications system that could perform at adramatically higher level thanHSDPA/HSUPA. The motivationbehind this development was to satisfy

growing demands from the market forenhanced specifications as well as toachieve a competitive mobile commu-nications system. At present, the com-mercial deployment of LTE is progress-ing well in Japan and elsewherethroughout the world and its high levelof performance is being recognized.Following Rel. 8, technologies forachieving a number of function exten-sions mainly in LTE upper layers weredeveloped and incorporated in Release9 specifications in 2009.

Next, as market demands continuedto intensify and as the need arose to sat-isfy the requirements of IMT-Advanced*8, which is a true fourth-gen-

eration mobile communications systemthen being standardized at ITU-R,3GPP set out in 2008 to formulate spec-ifications for LTE-Advanced with theaim of making further performanceimprovements and function extensionsto LTE. Those specifications were stan-dardized as Rel. 10 in 2011. LTE-Advanced was proposed as a candidatetechnology for ITU-R IMT-Advanced,and deliberations at ITU-R concludedthat LTE-Advanced did indeed satisfythe requirements of IMT-Advanced. InJanuary 2012, LTE-Advanced was for-mally approved as one radio interfaceof the IMT-Advanced system.

The formulation of Rel. 11 specifi-

*2 LTE-Advanced: Name of IMT-Advanced in3GPP. IMT-Advanced is the successor to theIMT-2000 third-generation mobile communi-cations system.

*3 Release 99: Indicates a version of 3GPPspecifications. Release 99 was formulated asthe initial 3GPP specification in 1999. TheHSDPA (see *4) function was added in 2005

as Release 5.*4 HSDPA: A high-speed downlink packet trans-

mission technology based on W-CDMA andstandardized by 3GPP. It optimizes the modu-lation method and coding rate according toreception conditions at the mobile terminal.

*5 HSUPA: A high-speed uplink packet transmis-sion technology based on W-CDMA and stan-

dardized by 3GPP. It optimizes the coding rate,spread factor, and transmission power accord-ing to reception conditions at the base station.

*6 IMT-2000: The 3G mobile communicationssystems for increasing the speed of communi-cation. These are summarized in ITU-R recom-mendations, and there are currently six varia-tions, including W-CDMA.


1999 2000

GSM/GPRS/EDGE enhancements

W-CDMA

1.28Mcps TDDRelease 4

ITU-R M.1457IMT-2000 Recommendation

ITU-R M.2012IMT-Advanced Recommendation

HSDPARelease 5

HSUPA, MBMSRelease 6

HSPA+ (MIMO, HOM etc.)Release 7

LTERelease 8

Release 9

LTE-AdvancedRelease 10Formally approved by ITU-R in January 2012

Release 11

Minor LTEenhancements

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

Release 99

Figure 1 Progression of 3GPP specifications

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6*7 ITU-R: A department of ITU, an organizationthat specializes in the field of telecommunica-tions. It manages and coordinates internationalmatters related to radio communication, suchas radio regulations and spectrum use in vari-ous countries.

*8 IMT-Advanced: A standard positioned as thesuccessor to IMT-2000 at ITU-R. It calls for

data rates of about 100 Mbit/s for high mobili-ty and 1 Gbit/s for low mobility.

*9 MIMO: A signal transmission technology thatimproves communications quality and spectralefficiency by using multiple transmitter andreceiver antennas for transmitting signals at thesame time and same frequency.

*10 FFR: A control method that allocates a differ-

ent frequency band to cell-edge UE.*11 Macrocell: Cellular communication area with

a radius of several hundred meters to severaltens of kilometers mainly covering outdoors.Usually, antennas are put up on towers or onroofs of buildings.


cations as function extensions of LTE-Advanced was energetically pursued at3GPP in 2012. Most of the specifica-tions were completed in 2012 and thefreezing of those specifications wasannounced in March 2013.

3. LTE Function Extensionsin Various Releases

At 3GPP, new functions have beenadded in various releases and exten-sions have been added to existing func-tions by applying enhanced technolo-gies. The correspondence between mainfunction extensions and recent releasesis shown in Figure 2. The followingdescribes the progression of extensionsmade for key LTE functions.

3.1 Bandwidth Widening

Technology

Widening the frequency bandwidthis an effective means of improving userthroughput. The bandwidth under W-

CDMA/HSDPA/HSUPA was 5 MHz,but LTE supported a maximum band-width of 20 MHz beginning with its ini-tial specifications in Rel. 8. Then, inLTE Rel. 10, carrier aggregation wasadopted with the aim of maintainingbackward compatibility while wideningbandwidth even further. This techniquemakes it possible to bundle multiplefrequency carriers of LTE Rel. 8 and tosupport a maximum bandwidth of 100MHz.

3.2 Multi-antenna Technology

In its initial Rel. 8 specifications,LTE adopted Multiple Input MultipleOutput (MIMO)*9 multi-antenna tech-nology in the downlink to increasetransmission speed and capacity. In Rel.8, the maximum number of layers(number of spatially multiplexed trans-mission signals) was four, but in Rel.10, the maximum number of layers inthe downlink was extended to eight and

support was initiated for a maximum offour MIMO layers in the uplink.

3.3 Inter-cell Coordination

Technology

As an effective measure for improv-ing cell-edge performance, inter-cellcoordination technology has beenactively studied for every release. First,in Rel. 8, Inter-Cell Interference Coor-dination (ICIC) technology was adopt-ed as an inter-base-station interface ontop of Fractional Frequency Reuse(FFR)*10, which applies frequency reusebetween cells only at the cell edge.Then, in Rel. 10, a Heterogeneous Net-work (HetNet) was adopted as a config-uration that could efficiently improvesystem capacity by overlaying largecells (macrocell*11) and small cells (pic-ocell*12/femtocell*13) having differenttransmission power levels. This releasealso initiated support of TransmissionPower Control (TPC)*14 for large cells


Variable bandwidthMax: 20 MHz

Carrier aggregation

Max: 100 MHz

Max. 8 layers in MIMO downlinkMax. 4 layers in MIMO uplink

Max. 4 layers in MIMO downlink

ICIC HetNet/eICIC

MTC:CNoverload

avoidance

eDDA, EPDCCHMTC:RANoverload

avoidance

FeICICCoMP

MMSE-IRCreceiver

Release 8

Bandwidth widening technology

Multi-antenna technology

Inter-cell coordination technology

Smartphone/machine communications technology

Interference rejection technology for UE

Release 9 Release 10 Release 11

Figure 2 Correspondence between main function extensions and releases

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7and enhanced ICIC (eICIC) for smallcells adopting current-cell identificationtechnology, both with the aim ofincreasing capacity and improving cell-edge performance in a HetNet configu-ration. Next, in Rel. 11, Furtherenhanced ICIC (FeICIC) was specifiedas a means of reducing interferencepower by canceling the reference signalemitted from a high transmission powercell at User Equipment (UE) connectedto a small cell.

In addition to the above, Coordinat-ed Multi-Point transmission/reception(CoMP) was specified for the first timein Rel. 11 to coordinate transmissionand reception signals among multiplebase stations. This technology adopts,for example, an intra-eNode B coordi-nation technique that enables UE toselect an optimal base station at highspeed and a technique that reducesinterference by halting transmissionfrom an adjacent base station whentransmitting to cell-edge UE.

3.4 Smartphone/Machine

Communications Technology

The demand for communicationservices between equipment withouthuman intervention is growing, andsuch services have become a topic ofstudy at 3GPP under the name ofMachine Type Communication (MTC).Support has been given, in particular, toa function called Core Network/RadioAccess Network (CN/RAN) overload

avoidance to prevent systemcongestion*15 when many devices suchas water-level sensors along rivers gen-erate transmissions in unison. In addi-tion, transmissions from an extremelylarge number of terminals can be envi-sioned due to the spread of MTC andsmartphone communications, and thereare concerns that the capacity of thePhysical Downlink Control CHannel(PDCCH)*16 will eventually fall short.A new downlink control channel calledEnhanced PDCCH (EPDCCH) wastherefore specified in Rel. 11 toincrease control channel capacity in thedownlink.

The ongoing expansion of smart-phone use is also creating a need forhandling various types of data traffic.Studies are therefore proceeding at3GPP on ways for the network to dealwith such traffic under the name ofDiverse Data Applications (DDA)*17. Inparticular, to optimize power consump-tion at UE, a function named enhancedDDA (eDDA) has been added in Rel.11 to enable UE to notify the networkthat it needs to reduce power consump-tion.

3.5 Interference Rejection

Technology for UE

To improve reception characteris-tics on the mobile-device side, recep-tion performance requirements havebeen specified in Rel. 11 under thename of Minimum Mean Squared

Error*18 - Interference Rejection Com-bining*19 (MMSE-IRC). A receiverequipped with MMSE-IRC generates areception weight*20 taking into accountan interference signal arriving fromanother cell thereby enabling that inter-ference to be effectively suppressed inaccordance with the receivers spatialdegrees of freedom*21.

3.6 Other Major Functions

Although details have been omittedin this article, extensions have also beenmade to the following functions in vari-ous LTE releases.(1) Home eNode B (HeNB): A low-

power LTE base station called afemtocell in the market. First speci-fied in Rel. 8, it is expected to beintroduced worldwide.

(2) Self-Organizing Network (SON): Afunction for automatically configur-ing or optimizing a system with theaim of reducing a telecommunica-tion carriers CAPital EXpenditure(CAPEX)*22 and OPerating EXpense(OPEX)*23. First specified in Rel. 8.

(3) Minimization of Drive Tests(MDT): A feature that aims toreduce an operators quality man-agement costs by equipping UEwith functions for measuring andrecording quality and notifying thenetwork of measurement results astraditionally done through drivetests conducted mainly by operatorsto manage service area quality. First

*12 Picocell: A cell having a radius up to severaltens of meters configured mainly for indooruse.

*13 Femtocell: A very small area with a radius ofseveral tens of meters covering homes and/orsmall shops.

*14 TPC: Function for controlling transmissionpower to maintain constant signal quality by

using the TPC information bit to inform thetransmitter of channel quality, packet errorrate, etc. as measured at the receiver.

*15 Congestion: A state where communicationrequests are concentrated inside a short timeperiod and exceed the processing capabilitiesof the network, thereby obstructing communi-cations.

*16 PDCCH: Control channel for the physicallayer in the downlink.

*17 DDA: A control method for dealing with vari-ous types of data traffic on the network.

*18 MMSE: A method for suppressing interfer-ence from other signals by multiplying thereceived signal with calculated weights.


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8*19 IRC: A method for rejecting an interferencesignal by creating an antenna-gain drop pointwith respect to the arrival direction of that sig-nal.

*20 Reception weight: Amount of fluctuation inamplitude and phase needed to synthesize andseparate signals received at multiple receiveantennas.

*21 Spatial degrees of freedom: Signal pro-cessing/separation performance obtained byincreasing the number of antennas.

*22 CAPEX: Amount of money expended forinvesting in facilities.

*23 OPEX: Amount of money expended for man-aging operations.

*24 Repeater: Relay equipment on the physical

layer to amplify a downlink receive signalfrom a base station and transmit it to a mobilestation.


specified in Rel. 10.(4) enhanced Multimedia Broadcast

Multicast Service (eMBMS): Afunction for orienting MBMS speci-fied for 3G systems to LTE. Firstspecified in Release 9.

(5) Relay Node: A node that aims toeffectively extend coverage. In con-trast to existing repeater*24 equip-ment, this is a regenerative relaynode that terminates not only in thephysical layer but in upper layerstoo. First specified in Rel. 10.

4. ConclusionThis article provided an overview

on the progression of LTE/LTE-Advanced standardization at 3GPP and

on main function extensions in variousLTE releases. Main features in Rel. 11,the latest set of 3GPP specifications,include HetNet-related technology,smartphone/machine-related technolo-gy, mobile-device interference-rejectiontechnology, M2M congestion counter-measure technology, and VoLTE roam-ing technology. The reader is asked tosee other articles in this issue for moredetails on these features [1]-[5].

References[1] Y. Kishiyama et al.: Heterogeneous Net-

work Capacity Expansion Technology for

Higher Speeds in LTE/LTE-Advanced,

NTT DOCOMO Technical Journal, Vol.

15, No. 2, pp. 9-17, Oct. 2013.

[2] Wuri A. Hapsari et al.: Radio System

Optimization toward Smartphone/machine

Communications for Higher Speeds in

LTE/LTE-Advanced, NTT DOCOMO

Technical Journal, Vol. 15, No. 2, pp.

18-26, Oct. 2013.

[3] Sagae et al.: Improved Interference Can-

celling and Suppression Technology in

LTE Release 11 Specifications, NTT

DOCOMO Technical Journal, Vol. 15, No.

2, pp. 27-30, Oct. 2013.

[4] Sasada et al.: Core Network Infrastructure

and Congestion Control Technology for

M2M Communications, NTT DOCOMO

Technical Journal, Vol. 15, No. 2, pp. 31-

36, Oct. 2013.

[5] Tanaka et al.: VoLTE Roaming and Inter-

connection Standard Technology, NTT

DOCOMO Technical Journal, Vol. 15, No.

2, pp. 37-41, Oct. 2013.


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