Advanced Technologies in LTE/LTE-Advanced

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

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

†0 LTE was standardized at 3GPP, an international standards Radio Access Network Development Department Takehiro Nakamura organization, as 3GPP Release 8 in 2008 with an eye to Sadayuki Abeta†0 achieving dramatic improvements over the third-generation Hideaki Takahashi†0 mobile communications system. This was followed by the Satoshi Nagata†0

Journal 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. Technical

3GPP Release 10 specifications (here- releases up to LTE Rel. 11. 1. Introduction inafter referred to as “Rel. 10”) making The 3rd Generation Partnership further enhancements to LTE. Never- 2. Progression of Project (3GPP), which had previously theless, market demands for enhanced 3GPP Specifications formulated the specifications for performance continued to grow and Since the formulation of W-CDMA WCDMA and High-Speed Packet diversify, and in 2012, 3GPP formulat- specifications as Release 99*3, many *1 DOCOMO Access (HSPA) as a third-generation ed Release 11 specifications (here- functions have been added at 3GPP in mobile communications system, formu- inafter referred to as “Rel. 11”) with the the form of new release specifications lated a radio system called Long Term aim of extending the functions and rais- in response to growing demands from Evolution (LTE) in 2008 as 3GPP ing the performance of LTE-Advanced. the market. The progression of these NTT Release 8 specifications (hereinafter In this article, we describe an overview specifications is shown in Figure 1. referred to as “Rel. 8”) in response to on how LTE specifications have pro- High-Speed Downlink Packet Access growing market demands. It then went gressed over the years and summarize (HSDPA)*4 and High-Speed Uplink on to formulate LTE-Advanced*2 as the main function extensions in the Packet Access (HSUPA)*5, which are

©2013 NTT DOCOMO, INC. *1 HSPA: A specification for increasing packet- Copies of articles may be reproduced only for per- data rates in W-CDMA and a general term sonal, noncommercial use, provided that the name encompassing HSDPA (see *4), which increases NTT DOCOMO Technical Journal, the name(s) of the speed from the base station to the mobile the author(s), the title and date of the article appear terminal, and HSUPA (see *5), which increas- in the copies. es the speed from the terminal to the base station.

4 NTT DOCOMO Technical Journal Vol. 15 No. 2 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

GSM/GPRS/EDGE enhancements

Release 99 W-CDMA

Release 4 1.28Mcps TDD

Release 5 HSDPA

Release 6 HSUPA, MBMS

Release 7 HSPA+ (MIMO, HOM etc.)

ITU-R M.1457 Release 8 LTE IMT-2000 Recommendation Minor LTE Release 9 enhancements

Journal Formally approved by ITU-R Release 10 LTE-Advanced in January 2012 ITU-R M.2012 IMT-Advanced Recommendation Release 11

Figure 1 Progression of 3GPP specifications

already in widespread use around the growing demands from the market for eration mobile communications system

Technical world, are included in Release 5 and enhanced specifications as well as to then being standardized at ITU-R, Release 6, respectively. These 3GPP achieve a competitive mobile commu- 3GPP set out in 2008 to formulate spec- specifications related to W-CDMA and nications system. At present, the com- ifications for LTE-Advanced with the HSDPA/HSUPA are contained in the mercial deployment of LTE is progress- aim of making further performance International Mobile Telecommunica- ing well in Japan and elsewhere improvements and function extensions tions-2000 (IMT-2000)*6 Recommenda- throughout the world and its high level to LTE. Those specifications were stan- tion of the International Telecommuni- of performance is being recognized. dardized as Rel. 10 in 2011. LTE- cation Union-Radiocommunication sec- Following Rel. 8, technologies for Advanced was proposed as a candidate *7 DOCOMO tor (ITU-R) . achieving a number of function exten- technology for ITU-R IMT-Advanced, The LTE system was formulated at sions mainly in LTE upper layers were and deliberations at ITU-R concluded 3GPP at the end of 2007 as Rel. 8 spec- developed and incorporated in Release that LTE-Advanced did indeed satisfy ifications to provide a mobile commu- 9 specifications in 2009. the requirements of IMT-Advanced. In NTT nications system that could perform at a Next, as market demands continued January 2012, LTE-Advanced was for- dramatically higher level than to intensify and as the need arose to sat- mally approved as one radio interface HSDPA/HSUPA. The motivation isfy the requirements of IMT- of the IMT-Advanced system. behind this development was to satisfy Advanced*8, which is a true fourth-gen- The formulation of Rel. 11 specifi-

*2 LTE-Advanced: Name of IMT-Advanced in as Release 5. dardized by 3GPP. It optimizes the coding rate, 3GPP. IMT-Advanced is the successor to the *4 HSDPA: A high-speed downlink packet trans- spread factor, and transmission power accord- IMT-2000 third-generation mobile communi- mission technology based on W-CDMA and ing to reception conditions at the base station. cations system. standardized by 3GPP. It optimizes the modu- *6 IMT-2000: The 3G mobile communications *3 Release 99: Indicates a version of 3GPP lation method and coding rate according to systems for increasing the speed of communi- specifications. Release 99 was formulated as reception conditions at the mobile terminal. cation. These are summarized in ITU-R recom- the initial 3GPP specification in 1999. The *5 HSUPA: A high-speed uplink packet transmis- mendations, and there are currently six varia- HSDPA (see *4) function was added in 2005 sion technology based on W-CDMA and stan- tions, including W-CDMA.

NTT DOCOMO Technical Journal Vol. 15 No. 2 5 Advanced Technologies in LTE/LTE-Advanced

cations as function extensions of LTE- CDMA/HSDPA/HSUPA was 5 MHz, support was initiated for a maximum of Advanced was energetically pursued at but LTE supported a maximum band- four MIMO layers in the uplink. 3GPP in 2012. Most of the specifica- width of 20 MHz beginning with its ini- tions were completed in 2012 and the tial specifications in Rel. 8. Then, in 3.3 Inter-cell Coordination freezing of those specifications was LTE Rel. 10, carrier aggregation was Technology announced in March 2013. adopted with the aim of maintaining As an effective measure for improv- backward compatibility while widening ing cell-edge performance, inter-cell 3. LTE Function Extensions bandwidth even further. This technique coordination technology has been in Various Releases makes it possible to bundle multiple actively studied for every release. First, At 3GPP, new functions have been frequency carriers of LTE Rel. 8 and to in Rel. 8, Inter-Cell Interference Coor- added in various releases and exten- support a maximum bandwidth of 100 dination (ICIC) technology was adopt- sions have been added to existing func- MHz. ed as an inter-base-station interface on tions by applying enhanced technolo- top of Fractional Frequency Reuse gies. The correspondence between main 3.2 Multi-antenna Technology (FFR)*10, which applies frequency reuse Journal function extensions and recent releases In its initial Rel. 8 specifications, between cells only at the cell edge. is shown in Figure 2. The following LTE adopted Multiple Input Multiple Then, in Rel. 10, a Heterogeneous Net- describes the progression of extensions Output (MIMO)*9 multi-antenna tech- work (HetNet) was adopted as a config- made for key LTE functions. nology in the downlink to increase uration that could efficiently improve transmission speed and capacity. In Rel. system capacity by overlaying large 3.1 Bandwidth Widening 8, the maximum number of layers cells (macrocell*11) and small cells (pic- Technology (number of spatially multiplexed trans- ocell*12/femtocell*13) having different

Technical Widening the frequency bandwidth mission signals) was four, but in Rel. transmission power levels. This release is an effective means of improving user 10, the maximum number of layers in also initiated support of Transmission throughput. The bandwidth under W- the downlink was extended to eight and Power Control (TPC)*14 for large cells

Release 8 Release 9 Release 10 Release 11

Carrier Variable bandwidth aggregation Bandwidth widening Max: 20 MHz technology Max: 100 MHz Max. 4 layers in MIMO Max. 8 layers in MIMO downlink Multi-antenna downlink Max. 4 layers in MIMO uplink

DOCOMO technology FeICIC Inter-cell coordination ICIC HetNet/eICIC CoMP technology eDDA, EPDCCH Smartphone/machine MTC:CN overload MTC:RAN communications technology avoidance overload avoidance

NTT MMSE-IRC Interference rejection technology for UE receiver

Figure 2 Correspondence between main function extensions and releases

*7 ITU-R: A department of ITU, an organization data rates of about 100 Mbit/s for high mobili- ent frequency band to cell-edge UE. that specializes in the field of telecommunica- ty and 1 Gbit/s for low mobility. *11 Macrocell: Cellular communication area with tions. It manages and coordinates international *9 MIMO: A signal transmission technology that a radius of several hundred meters to several matters related to radio communication, such improves communications quality and spectral tens of kilometers mainly covering outdoors. as radio regulations and spectrum use in vari- efficiency by using multiple transmitter and Usually, antennas are put up on towers or on ous countries. receiver antennas for transmitting signals at the roofs of buildings. *8 IMT-Advanced: A standard positioned as the same time and same frequency. successor to IMT-2000 at ITU-R. It calls for *10 FFR: A control method that allocates a differ-

6 NTT DOCOMO Technical Journal Vol. 15 No. 2 and enhanced ICIC (eICIC) for small avoidance to prevent system Error*18 - Interference Rejection Com- cells adopting current-cell identification congestion*15 when many devices such bining*19 (MMSE-IRC). A receiver technology, both with the aim of as water-level sensors along rivers gen- equipped with MMSE-IRC generates a increasing capacity and improving cell- erate transmissions in unison. In addi- reception weight*20 taking into account edge performance in a HetNet configu- tion, transmissions from an extremely an interference signal arriving from ration. Next, in Rel. 11, Further large number of terminals can be envi- another cell thereby enabling that inter- enhanced ICIC (FeICIC) was specified sioned due to the spread of MTC and ference to be effectively suppressed in as a means of reducing interference smartphone communications, and there accordance with the receiver’s spatial power by canceling the reference signal are concerns that the capacity of the degrees of freedom*21. emitted from a high transmission power Physical Downlink Control CHannel cell at User Equipment (UE) connected (PDCCH)*16 will eventually fall short. 3.6 Other Major Functions to a small cell. A new downlink control channel called Although details have been omitted In addition to the above, Coordinat- Enhanced PDCCH (EPDCCH) was in this article, extensions have also been ed Multi-Point transmission/reception therefore specified in Rel. 11 to made to the following functions in vari- Journal (CoMP) was specified for the first time increase control channel capacity in the ous LTE releases. in Rel. 11 to coordinate transmission downlink. (1) Home eNode B (HeNB): A low- and reception signals among multiple The ongoing expansion of smart- power LTE base station called a base stations. This technology adopts, phone use is also creating a need for femtocell in the market. First speci- for example, an intra-eNode B coordi- handling various types of data traffic. fied in Rel. 8, it is expected to be nation technique that enables UE to Studies are therefore proceeding at introduced worldwide. select an optimal base station at high 3GPP on ways for the network to deal (2) Self-Organizing Network (SON): A

Technical speed and a technique that reduces with such traffic under the name of function for automatically configur- interference by halting transmission Diverse Data Applications (DDA)*17. In ing or optimizing a system with the from an adjacent base station when particular, to optimize power consump- aim of reducing a telecommunica- transmitting to cell-edge UE. tion at UE, a function named enhanced tion carrier’s CAPital EXpenditure DDA (eDDA) has been added in Rel. (CAPEX)*22 and OPerating EXpense 3.4 Smartphone/Machine 11 to enable UE to notify the network (OPEX)*23. First specified in Rel. 8. Communications Technology that it needs to reduce power consump- (3) Minimization of Drive Tests The demand for communication tion. (MDT): A feature that aims to

DOCOMO services between equipment without reduce an operator’s quality man- human intervention is growing, and 3.5 Interference Rejection agement costs by equipping UE such services have become a topic of Technology for UE with functions for measuring and study at 3GPP under the name of To improve reception characteris- recording quality and notifying the NTT Machine Type Communication (MTC). tics on the mobile-device side, recep- network of measurement results as Support has been given, in particular, to tion performance requirements have traditionally done through drive a function called Core Network/Radio been specified in Rel. 11 under the tests conducted mainly by operators Access Network (CN/RAN) overload name of Minimum Mean Squared to manage service area quality. First

*12 Picocell: A cell having a radius up to several using the TPC information bit to inform the *16 PDCCH: Control channel for the physical tens of meters configured mainly for indoor transmitter of channel quality, packet error layer in the downlink. use. rate, etc. as measured at the receiver. *17 DDA: A control method for dealing with vari- *13 Femtocell: A very small area with a radius of *15 Congestion: A state where communication ous types of data traffic on the network. several tens of meters covering homes and/or requests are concentrated inside a short time *18 MMSE: A method for suppressing interfer- small shops. period and exceed the processing capabilities ence from other signals by multiplying the *14 TPC: Function for controlling transmission of the network, thereby obstructing communi- received signal with calculated weights. power to maintain constant signal quality by cations.

NTT DOCOMO Technical Journal Vol. 15 No. 2 7 Advanced Technologies in LTE/LTE-Advanced

specified in Rel. 10. on main function extensions in various Optimization toward Smartphone/machine (4) enhanced Multimedia Broadcast LTE releases. Main features in Rel. 11, Communications for Higher Speeds in LTE/LTE-Advanced,” NTT DOCOMO Multicast Service (eMBMS): A the latest set of 3GPP specifications, Technical Journal, Vol. 15, No. 2, pp. function for orienting MBMS speci- include HetNet-related technology, 18-26, Oct. 2013. fied for 3G systems to LTE. First smartphone/machine-related technolo- [3] Sagae et al.: “Improved Interference Can- specified in Release 9. gy, mobile-device interference-rejection celling and Suppression Technology in LTE Release 11 Specifications,” NTT (5) Relay Node: A node that aims to technology, M2M congestion counter- DOCOMO Technical Journal, Vol. 15, No. effectively extend coverage. In con- measure technology, and VoLTE roam- 2, pp. 27-30, Oct. 2013. *24 trast to existing repeater equip- ing technology. The reader is asked to [4] Sasada et al.: “Core Network Infrastructure ment, this is a regenerative relay see other articles in this issue for more and Congestion Control Technology for M2M Communications,” NTT DOCOMO node that terminates not only in the details on these features [1]-[5]. Technical Journal, Vol. 15, No. 2, pp. 31- physical layer but in upper layers 36, Oct. 2013. too. First specified in Rel. 10. References [5] Tanaka et al.: “VoLTE Roaming and Inter- [1] Y. Kishiyama et al.: “Heterogeneous Net- connection Standard Technology,” NTT Journal 4. Conclusion work Capacity Expansion Technology for DOCOMO Technical Journal, Vol. 15, No. Higher Speeds in LTE/LTE-Advanced,” 2, pp. 37-41, Oct. 2013. This article provided an overview NTT DOCOMO Technical Journal, Vol. on the progression of LTE/LTE- 15, No. 2, pp. 9-17, Oct. 2013. Advanced standardization at 3GPP and [2] Wuri A. Hapsari et al.: “Radio System Technical DOCOMO NTT

*19 IRC: A method for rejecting an interference *21 Spatial degrees of freedom: Signal pro- layer to amplify a downlink receive signal signal by creating an antenna-gain drop point cessing/separation performance obtained by from a base station and transmit it to a mobile with respect to the arrival direction of that sig- increasing the number of antennas. station. nal. *22 CAPEX: Amount of money expended for *20 Reception weight: Amount of fluctuation in investing in facilities. amplitude and phase needed to synthesize and *23 OPEX: Amount of money expended for man- separate signals received at multiple receive aging operations. antennas. *24 Repeater: Relay equipment on the physical

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