3GPP Long Term Evolution

LTE (Long Term Evolution) is the next major step in mobile radio communications, and will be introduced in 3rd Generation Partnership Project (3GPP) Release 8.

The aim of this 3GPP project is to improve the Universal Mobile Telecommunications System (UMTS) mobile phone standard and provide an enhanced user experience and simplified technology for next generation mobile broadband. Researchers and development engineers worldwide – representing more than 60 operators, vendors and research institutes – are participating in the joint LTE radio access standardization effort.

3GPP Release 8 is planned to be ratified as a standard in December 2008.

Overview

LTE meets key requirements of next generation networks including downlink peak rates of at least 100Mbit/s, 50 Mbit/s in the uplink and RAN (Radio Access Network) round-trip times of less than 10ms. LTE supports flexible carrier bandwidths, from 1.4MHz up to 20MHz as well as both FDD (Frequency Division Duplex) and TDD (Time Division Duplex).

The goals for LTE include improving spectral efficiency, lowering costs, improving services, making use of new spectrum and refarmed spectrum opportunities, and better integration with other open standards. The architecture that will result from this work is called EPS (Evolved Packet System) and comprises E-UTRAN (Evolved UTRAN) on the access side and EPC (Evolved Packet Core) on the core side. EPC is also known as SAE (System Architecture Evolution) and E-UTRAN is also known as LTE.

The main advantages with LTE are high throughput, low latency, plug and play from day one, FDD and TDD in the same platform, superior end-user experience and simple architecture resulting in low Operating Expenditures (OPEX). LTE will also support seamless connection to existing networks, such as GSM, CDMA and HSPA.

The standard includes the following technical characteristics:
* Peak download rates of 326.4 Mbit/s for 4x4 antennas, 172.8 Mbit/s for 2x2 antennas for every 20 MHz of spectrum.http://cp.literature.agilent.com/litweb/pdf/5989-7898EN.pdf]
* Peak upload rates of 86.4 Mbit/s for every 20 MHz of spectrum.
* At least 200 active users in every 5 MHz cell. (i.e., 200 active data clients)
* Sub-5ms latency for small IP packets
* Increased spectrum flexibility, with spectrum slices as small as 1.4 MHz (and as large as 20 MHz) supported (WCDMA requires 5 MHz slices, leading to some problems with roll-outs of the technology in countries where 5 MHz is a commonly allocated amount of spectrum, and is frequently already in use with legacy standards such as 2G GSM and cdmaOne.) Limiting sizes to 5 MHz also limited the amount of bandwidth per handset
* Optimal cell size of 5 km, 30 km sizes with reasonable performance, and up to 100 km cell sizes supported with acceptable performance
* Co-existence with legacy standards (users can transparently start a call or transfer of data in an area using an LTE standard, and, should coverage be unavailable, continue the operation without any action on their part using GSM/GPRS or WCDMA-based UMTS or even 3GPP2 networks such as CDMA or EV-DO)

Current State

While 3GPP Release 8 has yet to be ratified as a standard, much of the standard will be oriented around upgrading UMTS to a fourth generation mobile communications technology, which is essentially a mobile broadband system with enhanced multimedia services built on top.

A large amount of the work is aimed at simplifying the architecture of the system, as it transits from the existing UMTS circuit + packet switching combined network, to an all-IP flat architecture system.

Target requirements for LTE-Advanced have been set, expected to be part of 3GPP Release 10. LTE-Advanced will be a software upgrade for LTE networks and enable peak download rates over 1Gbit/s. It also targets higher spectral efficiency, faster switching between power states and improved performance at the cell edge.http://en.wikipedia.org/wiki/3GPP_Long_Term_Evolution#cite_note-2#cite_note-2]

Timetable

The LTE standard reached the functional freeze milestone in March 2008. Stage 2 Freeze is scheduled preliminary for June 2008 and official ratification in December 2008. The standard has been complete enough that hardware designers have been designing chipsets, test equipment and base stations for some time. LTE test equipment has been shipping from several vendors since early 2008 and at the Mobile World Congress 2008 in Barcelona Ericsson demonstrated the world’s first end-to-end mobile call enabled by LTE on a small handheld device [http://www.ericsson.com/ericsson/press/releases/20080210-1190029.shtml ] & Motorola demonstrated an LTE RAN standard compliant eNodeB and LTE chipset at the same event.

An "All IP Network" (AIPN)

A characteristic of next generation networks are that they are based upon the core internet protocol Transmission Control Protocol/Internet Protocol (TCP/IP). This provides users with richer communications experience including enhanced voice, video, and messaging services and advanced multimedia solutions.

In 2004, 3GPP proposed TCP/IP as the future for next generation networks and began feasibility studies into the so-called All IP Networks (AIPN.) Proposals developed included recommendations in 2005 for 3GPP Release 7 [ [http://www.3gpp.org/ftp/Specs/html-info/22978.htm 3GPP TR 22.978 All-IP network (AIPN) feasibility study] ] , which are the foundation of higher level protocols such as LTE. These recommendations are part of the 3GPP System Architecture Evolution (SAE). Some aspects of All-IP networks, however, were already defined as early as release 4 [ [http://www.3gpp.org/specs/WorkItem-info/WI--31067.htm 3GPP Work Item 31067] ] ).

From an architectural point-of-view the SAE/EPC architecture is defining an access independent, IP-based, flat network architecture with optimized interworking between legacy 3GPP and 3GPP2 networks. This means that both CDMA service providers and GSM/WCDMA service providers will be able to evolve their networks to LTE–SAE. A LTE–SAE network is designed for efficient support of mass-market usage of any IP-based service. The architecture is based on an evolution of the existing GSM/WCDMA core network, with simplified operations for a smooth and cost-efficient deployment.

The UMTS back-end becomes accessible through a variety of means, such as GSM's/UMTS's own radio network (GERAN, UTRAN, and E-UTRAN), WiFi, Ultra Mobile Broadband (UMB) and Worldwide Interoperability for Microwave Access (WiMAX). Users of non-UMTS radio networks would be provided with an entry-point into the IP network, with different levels of security depending on the trustworthiness of the network being used to make the connection. Users of GSM/UMTS networks would use an integrated system where all authentication at every level of the system is covered by a single system, while users accessing the UMTS network via WiMAX and other similar technologies would handle the WiMAX connection one way (for example, authenticating themselves via a MAC or ESN address) and the UMTS link-up another way.

E-UTRA Air Interface

Release 8's air interface, E-UTRA (Evolved UTRA, the E- prefix being common to the evolved equivalents of older UMTS components) would be used by UMTS operators deploying their own wireless networks. It's important to note that Release 8 is intended for use over any IP network, including WiMAX and WiFi, and even wired networks. [ [http://www.3gpp.org/Highlights/LTE/LTE.htm 3GPP LTE - See System Architecture Evolution] ]

The proposed E-UTRA system uses Orthogonal Frequency Division Multiple Access (OFDMA) for the downlink (tower to handset) and Single Carrier FDMA (SC-FDMA) for the uplink and employs multiple-input and multiple-output (MIMO) with up to four antennas per station. The channel coding scheme for transport blocks is turbo coding and a contention-free quadratic permutation polynomial (QPP) turbo code internal interleaver. [ [http://www.3gpp.org/ftp/Information/presentations/Presentations_3GPP-LTEv2.ppt 3GPP LTE presentation Kyoto May 22rd 2007] ]

The use of Orthogonal Frequency Division Multiplexing (OFDM), a system where the available spectrum is divided into thousands of very thin carriers, each on a different frequency, each carrying a part of the signal, enables E-UTRA to be much more flexible in its use of spectrum than the older CDMA based systems that dominated 3G. CDMA networks require large blocks of spectrum to be allocated to each carrier, to maintain high chip rates, and thus maximize efficiency. Building radios capable of coping with different chip rates (and spectrum bandwidths) is more complex than creating radios that only send and receive one size of carrier, so generally CDMA based systems standardize both. Standardizing on a fixed spectrum slice has consequences for the operators deploying the system: too narrow a spectrum slice would mean the efficiency and maximum bandwidth per handset suffers; too wide a spectrum slice, and there are deployment issues for operators short on spectrum. This became a major issue with the US roll-out of UMTS over WCDMA, where WCDMA's 5 MHz requirement often left no room in some markets for operators to co-deploy it with existing GSM standards.

LTE supports both FDD and TDD mode. Each mode has its own frame structure within LTE and these are aligned with each other meaning that similar hardware can be used in the base stations and terminals to allow for economy of scale. The TDD mode in LTE is aligned with TD-SCDMA as well allowing for coexistence. Ericsson demonstrated at the Mobile World Congress 2008 in Barcelona for the first time in the world both LTE FDD and TDD mode on the same base station platform.

Downlink

LTE uses OFDM for the downlink – that is, from the base station to the terminal. OFDM meets the LTE requirement for spectrum flexibility and enables cost-efficient solutions for very wide carriers with high peak rates. It is a well-established technology, for example in standards such as IEEE 802.11a/b/g, 802.16, HIPERLAN-2, DVB and DAB.

In the time domain you have a radio frame that is 10 ms long and consists of 10 sub frames of 1 ms each. Every sub frame consists of 2 slots where each slot is 0.5 ms. The subcarrier spacing in the frequency domain is 15 kHz. Twelve of these subcarriers together (per slot) is called a resource block so one resource block is 180 kHz. 6 Resource blocks fit in a carrier of 1.4 MHz and 100 resource blocks fit in a carrier of 20 MHz.

Supported modulation formats on the downlink data channels are QPSK, 16QAM and 64QAM.

For MIMO operation, a distinction is made between single user MIMO, for enhancing one users data throughput, and multi user MIMO for enhancing the cell throughput.

Uplink

In the uplink, LTE uses a pre-coded version of OFDM called Single Carrier Frequency Division Multiple Access (SC-FDMA). This is to compensate for a drawback with normal OFDM, which has a very high Peak to Average Power Ratio (PAPR). High PAPR requires expensive and inefficient power amplifiers with high requirements on linearity, which increases the cost of the terminal and drains the battery faster. SC-FDMA solves this problem by grouping together the resource blocks in such a way that reduces the need for linearity, and so power consumption, in the power amplifier. A low PAPR also improves coverage and the cell-edge performance.

Supported modulation formats on the uplink data channels are QPSK, 16QAM and 64QAM.

If virtual MIMO / Spatial division multiple access (SDMA) is introduced the data rate in the uplink direction can be increased depending on the number of antennas at the base station. With this technology more than one mobile can reuse the same resources. [http://www.presseecho.de/informationstechnologie/PR277867.htm Researchers demo 100 Mbit/s MIMO with SDMA / virtual MIMO technology] ]

Technology Demos

* In February 2007, Ericsson demonstrated for the first time in the world LTE with bit rates up to 144 Mbit/s [ [http://www.ericsson.com/ericsson/press/releases/20070209-1103814.shtml Ericsson demonstrates live LTE at 144mbps] ]

* In September 2006, Siemens Networks (today Nokia Siemens Networks) showed in collaboration with Nomor Research the first live emulation of a LTE network to the media and investors. As live applications two users streaming an HD-TV video in the downlink and playing an interactive game in the uplink have been demonstrated. [ [http://www.nomor.de/home/company/lte-demo-details Nomor Research: World's first LTE demonstration] ]

* The first presentation of an LTE demonstrator with HDTV streaming (>30 Mbit/s), video supervision and Mobile IP-based handover between the LTE radio demonstrator and the commercially available HSDPA radio system was shown during the ITU trade fair in Hong Kong in December 2006 by Siemens Communication Department.

* In September 2007, NTT DoCoMo demonstrated LTE data rates of 200 Mbit/s with power consumption below 100mW during the test. [ [http://www.electronicsweekly.com/Articles/2007/09/14/42179/ntt-docomo-develops-low-power-chip-for-3g-lte-handsets.htm NTT DoCoMo develops low power chip for 3G LTE handsets ] ]

* At the February 2008 Mobile World Congress::Motorola demonstrated how LTE can accelerate the delivery of personal media experience with HD video demo streaming, HD video blogging, Online gaming and VoIP over LTE running a RAN standard compliant LTE network & LTE chipset. [http://www.motorola.com/mediacenter/news/detailpf.jsp?globalObjectId=9249_9178_23] :Ericsson demonstrated the world’s first end-to-end LTE call on handheld and LTE FDD and TDD mode on the same base station platform. [ [http://www.teltarif.de/arch/2008/kw09/s29082.html Petzke, Kai "LTE: Der UMTS-Nachfolger steht in den Startlöchern", "teltarif.de", March 1 2008.] ] :Freescale Semiconductor demonstrated streaming HD video with peak data rates of 96 Mbit/s downlink and 86 Mbit/s uplink . [ [http://www.informationweek.com/hardware/showArticle.jhtml?articleID=206106780 Gardner, W. David. "Freescale Semiconductor To Demo LTE In Mobile Handsets", "Information Week", February 8 2008.] ] :NXP Semiconductors demonstrated a multi-mode LTE modem as the basis for a software-defined radio system for use in cellphones. [ [http://www.eetimes.com/conf/3gsm/showArticle.jhtml?articleID=206100262&kc=6437 Walko, John "NXP powers ahead with programmable LTE modem", "EETimes", January 30 2008.] ] :picoChip and mimoOn demonstrated an LTE base station reference design. This runs on a common hardware platform (multi-mode / software defined radio) together with their WiMAX architecture. [ [http://eetimes.eu/showArticle.jhtml?articleID=206103517 Walko, John "PicoChip, mimoOn team for LTE ref design", "EETimes", February 4 2008.] ]

* In March 2008, NTT DoCoMo demonstrated LTE data rates of 250 Mbit/s in an outdoor test. [ [http://www.nttdocomo.com/pr/2008/001390.html NTT DoCoMo Achieves 250Mbps Downlink in Super 3G Field Experiment] ]

* In April 2008, Motorola demonstrated the first EV-DO to LTE hand-off - handing over a streaming video from LTE to a commercial EV-DO network and back to LTE. [http://www.motorola.com/mediacenter/news/detailpf.jsp?globalObjectId=9422_9351_23]
* In April 2008, LG and Nortel demonstrated LTE data rates of 50 Mbit/s while travelling at 110 km/h. [ [http://wireless-watch.com/2008/04/06/nortel-and-lg-electronics-demo-lte-at-ctia-and-with-high-vehicle-speeds/ Nortel and LG Electronics Demo LTE at CTIA and with High Vehicle Speeds :: Wireless-Watch Community ] ]

* Researchers at Nokia Siemens Networks and Heinrich Hertz Institut have demonstrated LTE with 100 Mbit/s Uplink transfer speeds.

* On September 18, 2008, Mobile operator T-Mobile and Nortel Networks achieved data rates of up to 170 Mbit/s for downloads and up to 50 Mbit/s for uploads. T-Mobile, the wireless business of Deutsche Telekom acheived these speeds in a car in range of three cell sites on a highway in Bonn, Germany at an average speed of 67 kph.

Carrier adoption

*Most carriers supporting GSM or HSPA networks can be expected to upgrade their networks to LTE at some stage:
** AT&T Mobility has stated that they intend on upgrading to LTE as their 4G technology, but will introduce HSUPA and HSPA+ as bridge standards. [cite news|url=http://www.telecoms.com/itmgcontent/tcoms/news/articles/20017502859.html|title=AT&T develops wireless broadband plans|accessdate=2008-08-25]
** T-Mobile, Vodafone, France Télécom, Telia Sonera and Telecom Italia Mobile have also announced or talked publicly about their commitment to LTE.
*However, several networks that don't use these standards are also upgrading to LTE:
** Alltel, Verizon Wireless, the newly formed China Telecom/Unicom and Japan's KDDI have announced they have chosen LTE as their 4G network technology. This is significant, because these are CDMA carriers and are switching networking technologies to match what will likely be the 4G standard worldwide. [cite news|url=http://www.phonescoop.com/news/item.php?n=3026|title=Alltel Jumps on LTE Bandwagon|accessdate=2008-08-25] They have chosen to take the natural GSM evolution path as opposed to the 3GPP2 CDMA2000 evolution path Ultra Mobile Broadband (UMB). Verizon Wireless plans to begin LTE trials in 2008.cite news | first=Chris | last=Nuttall | coauthors= | title=Verizon set to begin trials of 4G network | date=2007-11-29 | publisher=The Financial Times | url =http://www.ft.com/cms/s/0/20cdb8b6-9ead-11dc-b4e4-0000779fd2ac.html | work =The Financial Times | pages = | accessdate = 2007-12-01 | language = ]
** Telus Mobility and Bell Mobility have announced that they will adopt LTE as its 4G wireless standard. [ [http://www.reportonbusiness.com/servlet/story/RTGAM.20080808.wtelus0808/BNStory/Business/home reportonbusiness.com: Wireless sales propel Telus results ] ]

Conformance testing

It has been suggested that TTCN-3 test specification language will be used for the purposes of LTE conformance testing. As of March 2008, TTCN-3 test suite development has been underway at ETSI. [ [http://portal.etsi.org/STFs%5CToR%5CToR160_2008_RP070835.doc Call for Experts for STF] ]

See also

* E-UTRA
* System Architecture Evolution
* HSPA

References

* H. Ekström, A. Furuskär, J. Karlsson, M. Meyer, S. Parkvall, J. Torsner, and M. Wahlqvist, "Technical Solutions for the 3G Long-Term Evolution," "IEEE Commun. Mag.", vol. 44, no. 3, March 2006, pp. 38–45
* 3rd Generation Partnership Project (3GPP); [http://www.3gpp.org/ftp/Specs/html-info/25913.htm Requirements for Evolved UTRA (E-UTRA) and Evolved UTRAN (E-UTRAN)]
* 3rd Generation Partnership Project (3GPP); Technical Specification Group Radio Access Network; [http://www.3gpp.org/ftp/Specs/html-info/25814.htm Physical Layer Aspects for Evolved UTRA]
* E. Dahlman, H. Ekström, A. Furuskär, Y. Jading, J. Karlsson, M. Lundevall, and S. Parkvall, "The 3G Long-Term Evolution - Radio Interface Concepts and Performance Evaluation," "IEEE Vehicular Technology Conference (VTC) 2006 Spring", Melbourne, Australia, May 2006
* C. Mathas, "LTE: From Zero to 32 Million in Three Years, says ABI Research," Mobile Handset Design Line, June 12, 2008. [http://www.mobilehandsetdesignline.com/news/208403661;jsessionid=TDYU4PMRQOOF0QSNDLPSKHSCJUNN2JVN]
* K. Fazel and S. Kaiser, "Multi-Carrier and Spread Spectrum Systems: From OFDM and MC-CDMA to LTE and WiMAX", 2nd Edition, John Wiley & Sons, 2008, ISBN 978-0-470-99821-2

External links for more information

* [http://www.3gpp.org/Highlights/LTE/LTE.htm 3GPP LTE page]
* [http://www.3gpp.org/ftp/Specs/archive/36_series/36.300/ 3GPP TS 36.300 Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description]
* [http://www.3gpp.org/specs/WorkItem-info/WI--31067.htm 3GPP AIPN Workitem]
* [http://www.nomor.de/home/technology/white-papers/progress-on-lte-advanced---the-future-4g-standard Nomor Research: White Paper on LTE Advance]
* [http://www.rohde-schwarz.com/www/dev_center.nsf/frameset?OpenAgent&website=com&navig=/www/dev_center.nsf/html/nav,10,11&content=/appnote/1MA111.html UMTS Long Term Evolution (LTE) Technology Introduction by Rohde & Schwarz]
* [http://www.ericsson.com/technology/research_papers/wireless_access/doc/the_3g_long_term_evolution_radio_interface.pdf "The Long Term Evolution of 3G" on Ericsson Review, no. 2, 2005]
* [http://www.signal.uu.se/Research/PCCWIP/Tunisia/WIP05_EAB.pdf "3G Long-Term Evolution" by Dr. Erik Dahlman at Ericsson Research]
* [http://www.calit2.net/events/pdfs/S3G_Stefan_Parkvall.pdf "Long-Term 3G Evolution - Radio Access" by Dr. Stefan Parkvall at Ericsson Research]
* [http://www.3gpp.org/ftp/PCG/PCG_16/PCG%20Beijing%20Workshop%20Presentations/3GPP%20Beijing%20workshop%20Courau%20TSG%20RAN%20Chairman.ppt "3GPP Evolution: LTE and SAE" by Francois Courau at Alcatel (Chairman of 3GPP TSG RAN)]
* [http://www.ikr.uni-stuttgart.de/Content/itg/fg524/Meetings/2006-09-29-Ulm/01-3GPP_LTE-SAE_Overview_Sep06.pdf "3GPP Long-Term Evolution / System Architecture Evolution: Overview" by Ulrich Barth at Alcatel]
* [http://www.elsevier.com/wps/find/bookdescription.cws_home/710717/description#description Dahlman, Parkvall, Skold and Beming, 3G Evolution: HSPA and LTE for Mobile Broadband, Academic Press, Oxford, UK, 2007]
* [http://www.krnet.or.kr/board/include/download.asp?no=30&db=program&fileno=2 "3GPP LTE & 3GPP2 LTE Standardization" by Dr. Lee, HyeonWoo at Samsung Electronics]
* [http://www.3gamericas.org/English/pdfs/wp_UMTS_Rel7_Beyond_FINAL.pdf "Mobile Broadband: The Global Evolution of UMTS/HSPA - 3GPP Release 7 and Beyond" by 3G Americas]
* [http://www.comnets.uni-bremen.de/typo3site/uploads/media/ITG-FA52-Schopp-Bremen-Nov-2006.pdf "Trends in Mobile Network Architectures" by Dr. Michael Schopp at Siemens Networks]
* [http://www.hhi.fraunhofer.de/ Fraunhofer Heinrich-Hertz-Institut]
* [http://www.freescale.com/files/wireless_comm/doc/white_paper/3GPPEVOLUTIONWP.pdf "Overview of the 3GPP LTE Physical Layer" by James Zyren and Dr. Wes McCoy, Freescale Semiconductor]
* [http://www.ericsson.com/technology/whitepapers/lte_overview.pdf Long Term Evolution (LTE): An Introduction – Ericsson White Paper]