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.[1][2] 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 Stockholm and Oslo on 14 December 2009. LTE is the natural upgrade path for carriers with GSM/UMTS networks, but even CDMA holdouts such as Verizon in North America and au by KDDI in Japan have announced that they will migrate to LTE in the future. 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.
Contents |
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 in the beginning of the new millennium. Its wireless interface is incompatible with 2G and 3G networks, and so 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 phone[3][4] and HTC ThunderBolt offered by Verizon starting on March 17 being the second LTE phone to be sold commercially[5][6]. 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.[7] Services are expected to commence in 2013.[8]
The LTE specification provides down-link 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 support for 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.[9] 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 when compared to HSPA[10]).
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:
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.[13] 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.
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.[14][15][16][17] As a result, phones from one country may not work in other countries. Users will need a multi-band capable phone for roaming internationally.
Countries with commercial LTE service (as of December 2011)[18]
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||