LTE (telecommunication)

3GPP Long Term Evolution, usually referred to as LTE, is a standard for wireless communication of high-speed data for mobile phones and data terminals. It is based on the GSM/EDGE and UMTS/HSPA network technologies, increasing the capacity and speed using new modulation techniques. The standard is developed by the 3GPP (3rd Generation Partnership Project).

The world's first publicly available LTE service was launched by TeliaSonera in the Scandinavian capitals Oslo and Stockholm on 14 December 2009. LTE is the natural upgrade path for carriers with GSM/UMTS networks, but even CDMA holdouts such as Verizon Wireless, who launched the first large-scale LTE network in North America in 2010, and au by KDDI in Japan have announced they will migrate to LTE. LTE is, therefore, anticipated to become the first truly global mobile phone standard.

Although commonly referred to as a type of 4G wireless service, LTE release 8 currently in use does not satisfy the requirements set forth by the ITU-R organization. Future releases of LTE (referred to as LTE Advanced) are expected to satisfy the requirements to be considered 4G.

Overview

See also: LTE timeline

Telia-branded Samsung LTE modem

File:HTC Thunderbolt.JPG

HTC ThunderBolt, the second commercially available LTE smartphone

LTE is a standard for wireless data communications technology and an evolution of the GSM/UMTS standards. The goal of LTE is to increase the capacity and speed of wireless data networks using new DSP (Digital Signal Processing) techniques and modulations that were developed around the turn of the millennium. Its wireless interface is incompatible with 2G and 3G networks, so that it must be operated on a separate wireless spectrum.

LTE was first proposed by NTT DoCoMo of Japan in 2004. The standard was finalized in December 2008, and the first publicly available LTE service was launched by TeliaSonera in the Scandinavian capitals Stockholm and Oslo on December 14, 2009 as a data connection with a USB modem. In 2011, LTE services were launched by major North American carriers as well, with the Samsung Galaxy Indulge offered by MetroPCS starting on February 10, 2011 being the first commercially available LTE smartphone and HTC ThunderBolt offered by Verizon starting on March 17 being the second LTE smartphone to be sold commercially. Initially, CDMA operators planned to upgrade to a rival standard called the UMB, but all the major CDMA operators (such as Verizon, Sprint and MetroPCS in the United States, Bell and Telus in Canada, au by KDDI in Japan, SK Telecom in South Korea and China Telecom/China Unicom in China) have announced that they intend to migrate to LTE after all. The evolution of LTE is LTE Advanced, which was standardized in March 2011. Services are expected to commence in 2013.

The LTE specification provides downlink peak rates of 300 Mbit/s, uplink peak rates of 75 Mbit/s and QoS provisions permitting round-trip times of less than 10 ms. LTE has the ability to manage fast-moving mobiles and supports multi-cast and broadcast streams. LTE supports scalable carrier bandwidths, from 1.4 MHz to 20 MHz and supports both frequency division duplexing (FDD) and time-division duplexing (TDD). The architecture of the network is simplified to a flat IP-based network architecture called the Evolved Packet Core (EPC), designed to replace the GPRS Core Network and support seamless handovers for both voice and data to cell towers with older network technology such as GSM, UMTS and CDMA2000. The simpler architecture results in lower operating costs (for example, each E-UTRAN cell will support up to four times the data and voice capacity supported by HSPA).

Features

See also: E-UTRA

Much of the standard addresses upgrading 3G UMTS to what will eventually be 4G mobile communications technology. 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. E-UTRA is the air interface of LTE. Its main features are:

• Peak download rates up to 3 Gbit/s and upload rates up to 1.5 Gbit/s depending on the user equipment category (with 8x8 antennas using 20 MHz of spectrum). Eight 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.
• Low data transfer latencies (sub-5 ms latency for small IP packets in optimal conditions), lower latencies for handover and connection setup time than with previous radio access technologies.
• Improved support for mobility, exemplified by support for terminals moving at up to 350 km/h or 500 km/h depending on the frequency band.
• OFDMA for the downlink, SC-FDMA for the uplink to conserve power
• Support for both FDD and TDD communication systems as well as half-duplex FDD with the same radio access technology
• Support for all frequency bands currently used by IMT systems by ITU-R.
• Increased spectrum flexibility: 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz wide cells are standardized. (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.)
• Support for cell sizes from tens of metres radius (femto and picocells) up to 100 km radius macrocells. In the lower frequency bands to be used in rural areas, 5 km is the optimal cell size, 30 km having reasonable performance, and up to 100 km cell sizes supported with acceptable performance. In city and urban areas, higher frequency bands (such as 2.6 GHz in EU) are used to support high speed mobile broadband. In this case, cell sizes may be 1 km or even less.
• Supports at least 200 active data clients in every 5 MHz cell.
• Simplified architecture: The network side of E-UTRAN is composed only of eNode Bs
• Support for inter-operation and co-existence with legacy standards (e.g. GSM/EDGE, UMTS and CDMA2000). Users can 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)
• Packet switched radio interface.
• 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.

Voice calls

LTE CSFB to GSM/UMTS network interconnects

The LTE standard only supports packet switching with its all-IP network. Voice calls in GSM, UMTS and CDMA2000 are circuit switched, so with the adoption of LTE, carriers will have to re-engineer their voice call network. Three different approaches sprang up. Most major backers of LTE preferred and promoted VoLTE (Voice over LTE, an implementation of IP Multimedia Subsystem or IMS) from the beginning. The lack of software support in initial LTE devices as well as core network devices however led to a number of carriers promoting VoLGA (Voice over LTE Generic Access) as an interim solution. The idea was to use the same principles as GAN (Generic Access Network, also known as UMA or Unlicensed Mobile Access), which defines the protocols through which a mobile handset can perform voice calls over a customer's private Internet connection, usually over wireless LAN. VoLGA however never gained much support, because VoLTE (IMS) promises much more flexible services, albeit at the cost of having to upgrade the entire voice call infrastructure. While the industry has seemingly standardized on VoLTE for the future, the demand for voice calls today has led LTE carriers to introduce CSFB (Circuit Switched Fallback) as a stopgap measure. When placing or receiving a voice call, LTE handsets will fall back to old 2G or 3G networks for the duration of the call.

Frequency bands

See also: E-UTRA § Frequency bands and channel bandwidths

The LTE standard can be used with many different frequency bands. In North America, 700 and 1700 MHz are planned to be used; 800, 1800, 2600 MHz in Europe; 1800 and 2600 MHz in Asia; and 1800 MHz in Australia. As a result, phones from one country may not work in other countries. Users will need a multi-band capable phone for roaming internationally.

Presence

Main article: List of LTE networks

Adoption of LTE technology as of January 5, 2012.

  Countries with commercial LTE service

  Countries with commercial LTE network deployment on-going or planned

  Countries with LTE trial systems (pre-commitment)

Countries with commercial LTE service (as of January 2012):

• Armenia
• Austria
• Australia
• Bahrain
• Belarus
• Brazil
• Bulgaria
• Canada
• Denmark
• Estonia
• Finland
• Germany
• Hong Kong
• Hungary
• Japan
• Korea, South
• Kuwait
• Latvia
• Lithuania
• Norway
• Poland
• Puerto Rico
• Russia (launched on January 15, 2012)
• Saudi Arabia
• Singapore
• Spain
• Sweden
• United Arab Emirates
• Uruguay
• United States
• Uzbekistan

See also

• Comparison of wireless data standards
• E-UTRA - the radio access network used in LTE
• Flat IP – flat IP architectures in mobile networks
• LTE Advanced - the successor to LTE
• LSTI - LTE SAE Trial Initiative
• System architecture evolution - the re-architecturing of core networks in LTE
• TD-LTE (LTE TDD) - an alternative LTE standard developed by China
• UMB - a proposed rival to LTE, never commercialized
• WiMAX - a competitor to LTE
• Zadoff–Chu sequence
• Next Generation Networking

Further reading

• Erik Dahlman, Stefan Parkvall, Johan Sköld "4G – LTE/LTE-Advanced for Mobile Broadband", Academic Press, 2011, ISBN 978-0-12-385489-6
• Stefania Sesia, Issam Toufik, and Matthew Baker, "LTE – The UMTS Long Term Evolution – From Theory to Practice", Second Edition including Release 10 for LTE-Advanced, John Wiley & Sons, 2011, ISBN 978-0-470-66025-6
• Chris Johnson, "LTE in BULLETS", CreateSpace, 2010, ISBN 978-1-4528-3464-1
• Erik Dahlman, Stefan Parkvall, Johan Sköld, Per Beming, "3G Evolution – HSPA and LTE for Mobile Broadband", 2nd edition, Academic Press, 2008, ISBN 978-0-12-374538-5
• Borko Furht, Syed A. Ahson, "Long Term Evolution: 3GPP LTE Radio And Cellular Technology", Crc Press, 2009, ISBN 978-1-4200-7210-5
• 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
• Agilent Technologies, "LTE and the Evolution to 4G Wireless: Design and Measurement Challenges", John Wiley & Sons, 2009 ISBN 978-0-470-68261-6
• Sajal Kumar Das, John Wiley & Sons (April 2010): "Mobile Handset Design", ISBN 978-0-470-82467-2 .
• Beaver, Paul, "What is TD-LTE?", RF&Microwave Designline, September 2011.

External links

• LTE homepage from the 3GPP website
• LTE A-Z Description 3GPP LTE Encyclopedia

White papers and other technical information

• LTE Technology Overview and Tutorial Series including Webinars and Video presentations
• "The Long Term Evolution of 3G" on Ericsson Review, no. 2, 2005
• LTE technology introduction
• "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
• The 3G Long-Term Evolution – Radio Interface Concepts and Performance Evaluation
• LTE and the Evolution to 4G Wireless Design and Measurement Challenges – "LTE Security"
• Role of Crypto in Mobile Communications "LTE Security"