LTE (telecommunication)

LTE (Long Term Evolution) is the last step toward the 4th generation of radio technologies designed to increase the capacity and speed of mobile telephone networks. Where the current generation of mobile telecommunication networks are collectively known as 3G, LTE is marketed as and called 4G, although technically it is 3.9G. Most major mobile carriers in the United States and several worldwide carriers have announced plans to convert their networks to LTE beginning in 2009. LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) which will be introduced in 3rd Generation Partnership Project (3GPP) Release 8. Much of 3GPP Release 8 will focus on adopting 4G mobile communications technology, including an all-IP flat networking architecture.

Overview

LTE could allow data transfer rates to and from mobile devices between 15 and 100 times faster than 3G networks.

LTE provides 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 10 ms. LTE supports flexible carrier bandwidths, from 1.4 MHz up to 20 MHz as well as both FDD (Frequency Division Duplexing) and TDD (Time Division Duplex).

The goals for LTE include improving spectral efficiency, lowering costs, improving services, making use of new spectrum and reformed 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, FDD and TDD in the same platform, improved end-user experience and simple architecture resulting in low operating expenditures. LTE will also support seamless passing to cell towers with older network technology such as GSM, cdmaOne, W-CDMA (UMTS), and CDMA2000.

Current state

While 3GPP Release 8 is an unratified, formative standard, much of the Release addresses upgrading 3G UMTS to 4G mobile communications technology, which is essentially a mobile broadband system with enhanced multimedia services built on top.

The standard includes:

• Peak download rates of 326.4 Mbit/s for 4x4 antennas, 172.8 Mbit/s for 2x2 antennas for every 20 MHz of spectrum.
• Peak upload rates of 86.4 Mbit/s for every 20 MHz of spectrum.
• 5 different terminal classes have been defined from a voice centric class up to a high end terminal that supports the peak data rates. All terminals will be able to process 20 MHz bandwidth.
• At least 200 active users in every 5 MHz cell. (specifically, 200 active data clients)
• Sub-5ms latency for small IP packets
• Increased spectrum flexibility, with spectrum slices as small as 1.5 MHz (and as large as 20 MHz) supported (W-CDMA 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 W-CDMA-based UMTS or even 3GPP2 networks such as cdmaOne or CDMA2000)
• Support for MBSFN (Multicast Broadcast Single Frequency Network). This feature can deliver services such as Mobile TV using the LTE infrastructure, and is a competitor for DVB-H-based TV broadcast.
• PU²RC as a practical solution for MU-MIMO. The detailed procedure for the general MU-MIMO operation is handed to the next release, e.g., LTE-Advanced, where further discussions will be held.

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.

Timetable

In December 2008, Rel-8 specification was locked. In January 2009, the ASN.1 code was locked. 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. Motorola demonstrated a 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 Internet Protocol (IP). See, for example, the Next Generation Mobile Networks Alliance (NGMN).

In 2004, 3GPP proposed IP as the future for next generation networks and began feasibility studies into All IP Networks (AIPN). Proposals developed included recommendations for 3GPP Release 7(2005), 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.

The 3GPP is defining IP-based, flat network architecture as part of the System Architecture Evolution (SAE) effort. LTE–SAE architecture and concepts have been 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 and smooth, cost-efficient deployment.

E-UTRAN Air Interface

Release 8's air interface, E-UTRA (Evolved UTRAN, 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.

The proposed E-UTRAN system uses OFDMA for the downlink (tower to handset) and Single Carrier FDMA (SC-FDMA) for the uplink and employs 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.

The use of Orthogonal frequency-division multiplexing (OFDM), a system where the available spectrum is divided into many thin carriers, each on a different frequency, each carrying a part of the signal, enables E-UTRAN 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 W-CDMA, where W-CDMA'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. While FDD makes use of paired spectra for UL and DL transmission separated by a duplex frequency gap, TDD is alternating using the same spectral resources used for UL and DL, separated by guard time. 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 MWC 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/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.

In the downlink there are three different physical channels. The Physical Downlink Shared Channel (PDSCH) is used for all the data transmission, the Physical Multicast Channel (PMCH) is used for broadcast transmission using a Single Frequency Network and the Physical Broadcast Channel (PBCH) is used to send most important system information within the cell. Supported modulation formats on the PDSCH are QPSK, 16QAM and 64QAM.

For MIMO operation, a distinction is made between single user MIMO, for enhancing one user's 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 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.

In the uplink there are two physical channels. While the Physical Random Access Channel (PRACH) is only used for initial access and when the UE is not uplink synchronized, all the data is being send on the Physical Uplink Shared Channel (PUSCH). Supported modulation formats on the uplink data channel 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.

Frequency bands and channel bandwidths

From Tables 5.5-1 "E-UTRA Operating Bands" and 5.6.1-1 "E-UTRA Channel Bandwidth" of 3GPP TS 36.101 (Release 8.4.0), the following table lists the specified frequency bands of LTE and the channel bandwidths each listed band supports:

E-UTRA Operating Band	Uplink (UL) Operating Band BS Receive UE Transmit	Downlink (DL) Operating Band BS Transmit UE Receive	Duplex Mode	Channel Bandwidths (MHz)	Alias	Region(s)
001 I (1)	017 1920 MHz to 1980 MHz	017 2110 MHz to 2170 MHz	FDD	5, 10, 15, 20	UMTS IMT	Japan
002 II (2)	012 1850 MHz to 1910 MHz	012 1930 MHz to 1990 MHz	FDD	1.4, 3, 5, 10, 15, 20	PCS
003 III (3)	010 1710 MHz to 1785 MHz	010 1805 MHz to 1880 MHz	FDD	1.4, 3, 5, 10, 15, 20	DCS 1800	Finland, Hong Kong
004 IV (4)	009 1710 MHz to 1755 MHz	013 2110 MHz to 2155 MHz	FDD	1.4, 3, 5, 10, 15, 20	AWS	US
005 V (5)	005 824 MHz to 849 MHz	005 869 MHz to 894MHz	FDD	1.4, 3, 5, 10	Cellular 850	US, Australia
006 VI (6)	006 830 MHz to 840 MHz	006 875 MHz to 885 MHz	FDD	5, 10		Japan
007 VII (7)	021 2500 MHz to 2570 MHz	021 2620 MHz to 2690 MHz	FDD	5, 10, 15, 20	IMT-E	EU
008 VIII (8)	007880 MHz to 915 MHz	007925 MHz to 960 MHz	FDD	1.4, 3, 5, 10	GSM, UMTS900
009 IX (9)	012 1749.9 MHz to 1784.9 MHz	011 1844.9 MHz to 1879.9 MHz	FDD	5, 10, 15, 20		US, Japan
010 X (10)	011 1710 MHz to 1770 MHz	013 2110 MHz to 2170 MHz	FDD	5, 10, 15, 20	UMTS,IMT 2000	Brazil, Uruguay, Ecuador, Peru
011 XI (11)	008 1427.9 MHz to 1452.9 MHz	008 1475.9 MHz to 1500.9 MHz	FDD	5, 10, 15, 20	PDC	Japan (Softbank, KDDI, DoCoMo)
012 XII (12)	001 698 MHz to 716 MHz	001 728 MHz to 746 MHz	FDD	1.4, 3, 5, 10
013 XIII (13)	003 777 MHz to 787 MHz	003 746 MHz to 756 MHz	FDD	1.4, 3, 5, 10	Verizon's 700 MHz Block C
014 XIV (14)	004 788 MHz to 798 MHz	004 758 MHz to 768 MHz	FDD	1.4, 3, 5, 10
017 XVII (17)	002 704 MHz to 716 MHz	002 734 MHz to 746 MHz	FDD	1.4, 3, 5, 10	AT&T's 700 MHz Block B
033 XXXIII (33)	016 1900 MHz to 1920 MHz		TDD	5, 10, 15, 20
034 XXXIV (34)	020 2010 MHz to 2025 MHz		TDD	5, 10, 15
035 XXXV (35)	014 1850 MHz to 1910 MHz		TDD	1.4, 3, 5, 10, 15, 20
036 XXXVI (36)	019 1930 MHz to 1990 MHz		TDD	1.4, 3, 5, 10, 15, 20
037 XXXVII (37)	017 1910 MHz to 1930 MHz		TDD	5, 10, 15, 20
038 XXXVIII (38)	023 2570 MHz to 2620 MHz		TDD	5, 10		EU
039 XXXIX (39)	015 1880 MHz to 1920 MHz		TDD	5, 10, 15, 20
040 XL (40)	021 2300 MHz to 2400 MHz		TDD	10, 15, 20	IMT-2000	China

Technology Demos

• 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.
• 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 February 2007, Ericsson demonstrated for the first time in the world LTE with bit rates up to 144 Mbit/s
• In September 2007, NTT docomo demonstrated LTE data rates of 200 Mbit/s with power consumption below 100 mW during the test.
• At the February 2008 Mobile World Congress:
  • Huawei demonstrated Long Term Evolution ("LTE") applications by means of multiplex HDTV services and mutual gaming that has transmission speeds of 100 Mbps.
  • 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.
  • Ericsson demonstrated the world’s first end-to-end LTE call on handheld Ericsson demonstrated LTE FDD and TDD mode on the same base station platform.
  • Freescale Semiconductor demonstrated streaming HD video with peak data rates of 96 Mbit/s downlink and 86 Mbit/s uplink.
  • NXP Semiconductors demonstrated a multi-mode LTE modem as the basis for a software-defined radio system for use in cellphones.
  • picoChip and Mimoon demonstrated a base station reference design. This runs on a common hardware platform (multi-mode / software defined radio) with their WiMAX architecture.
• 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.
• In April 2008, LG Electronics and Nortel demonstrated LTE data rates of 50 Mbit/s while travelling at 110 km/h.
• In April 2008 Ericsson unveiled its M700 mobile platform, the world’s first commercially available LTE-capable platform, with peak data rates of up to 100 Mbit/s in the downlink and up to 50 Mbit/s in the uplink. The first products based on M700 will be data devices such as laptop modems, Expresscards and USB modems for notebooks, as well other small-form modems suitable for consumer electronic devices. Commercial release is set for 2009, with products based on the platform expected in 2010.
• Researchers at Nokia Siemens Networks and Heinrich Hertz Institut have demonstrated LTE with 100 Mbit/s Uplink transfer speeds.
• At the February 2009 Mobile World Congress:
  • Huawei demonstrated the world' s first unified frequency-division duplex and time-division duplex (FDD/TDD) long-term evolution (LTE) solution.
  • Aricent gave a demonstration of LTE eNodeB layer2 stacks.
  • Setcom Streaming a Video
  • Infineon demonstrated a single-chip 65nm CMOS RF transceiver providing 2G/3G/LTE functionality
• In May 2009 **Setcom** Streaming HD Video at GSMA MWC and LTE World Summit

Carrier adoption

Most carriers supporting GSM or HSUPA networks can be expected to upgrade their networks to LTE at some stage:

• Rogers Wireless has stated that they intend on initially launching their LTE network in Vancouver by February 2010, just in time for the Winter Olympics.
• AT&T Mobility has stated that they intend on upgrading to LTE as their 4G technology in 2011, but will introduce HSUPA and HSPA+ as bridge standards.
• TeliaSonera has started network built up in Stockholm and Oslo, and will follow up in Copenhagen when a license in Denmark has been bought/granted. The networks are still only for testing. There are no indication of a public live date.
• In January 2009 TeliaSonera signed a contract for an LTE network with Huawei covering Oslo, Norway. Under the agreement, Huawei will provide an end-to-end LTE solution including LTE base stations, core network and OSS (Operating Support System).
• In January 2009 Ericsson and TeliaSonera announced the signing of a commercial LTE network. The roll-out of the 4G mobile broadband network will offer the highest data rates ever realized, with the best interactivity and quality. This network will cover Sweden’s capital Stockholm and the contract is Ericsson’s first for commercial deployment of LTE.
• T-Mobile, Vodafone, France Télécom and Telecom Italia Mobile have also announced or talked publicly about their commitment to LTE.

Despite initial development of the rival UMB standard, which was designed as an upgrade path for CDMA networks, most operators of networks based upon the latter system have also announced their intent to migrate to LTE, resulting in discontinuation of UMB development.

• Verizon Wireless is presently testing its LTE network and selects Ericsson and Alcatel-Lucent as Primary Network Vendors for LTE Network.
• Bell Mobility plans to start LTE deployment in 2009-2010
• Telus Mobility has announced that it will adopt LTE as its 4G wireless standard.
• MetroPCS recently announced that it would be using LTE for its upcoming 4G network.
• The newly formed China Telecom/China Unicom and Japan's KDDI have announced they have chosen LTE as their 4G network technology.
• Cox Communications has its first tower for wireless LTE network build-out. Wireless services should launch late 2009.

See also

• E-UTRA
• System Architecture Evolution

Further reading

• Stefania Sesia, Issam Toufik, and Matthew Baker, "LTE - The UMTS Long Term Evolution - From Theory to Practice", John Wiley & Sons, 2009, ISBN 978-0470697160
• F. Khan, "LTE for 4G Mobile Broadband - Air Interface Technologies and Performance", Cambridge University Press, 2009
• Mustafa Ergen, "Mobile Broadband - Including WiMAX and LTE", Springer, NY, 2009
• 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
• 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
• 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

• 3GPP LTE homepage
• Public LTE Discussion Forum

3GPP Projects and Presentations

• 3GPP TS 36.300 Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description
• 3GPP AIPN Workitem
• "3GPP Evolution: LTE and SAE" by Francois Courau at Alcatel (Chairman of 3GPP TSG RAN)

Specifications

• 3rd Generation Partnership Project (3GPP); Requirements for Evolved UTRA (E-UTRA) and Evolved UTRAN (E-UTRAN)
• 3rd Generation Partnership Project (3GPP); Technical Specification Group Radio Access Network; Physical Layer Aspects for Evolved UTRA

Industry reaction

• "Mobile Broadband: The Global Evolution of UMTS/HSPA - 3GPP Release 7 and Beyond" by 3G Americas
• Experience LTE by Motorola
• Verizon Wireless Global LTE Deployment Plans

Whitepapers and other information

• EDGE, HSPA, LTE: Broadband Innovation (PDF)
• "LTE performance for initial deployments" by Nokia Siemens Networks
• Long Term Evolution (LTE): An Introduction – Ericsson White Paper "The Long Term Evolution of 3G" on Ericsson Review, no. 2, 2005
• "3G Long-Term Evolution" by Dr. Erik Dahlman at Ericsson Research
• "Long-Term 3G Evolution - Radio Access" by Dr. Stefan Parkvall at Ericsson Research
• "3GPP Long-Term Evolution / System Architecture Evolution: Overview" by Ulrich Barth at Alcatel
• Dahlman, Parkvall, Skold and Beming, 3G Evolution: HSPA and LTE for Mobile Broadband, Academic Press, Oxford, UK, 2007
• 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
• "3GPP LTE & 3GPP2 LTE Standardization" by Dr. Lee, HyeonWoo at Samsung Electronics
• Nomor Research Newsletter: Overview LTE Time Division Duplex
• "Trends in Mobile Network Architectures" by Dr. Michael Schopp at Siemens Networks
• "Overview of the 3GPP LTE Physical Layer" by James Zyren and Dr. Wes McCoy, Freescale Semiconductor
• “Growing momentum brings LTE closer to becoming a commercial reality”
• 3GPP LTE - series of pages looking at different aspects of 3G LTE
• LTE technology introduction