In telecommunications, Long-Term Evolution LTE is a standard for wireless broadband communication for mobile devices and data terminals, based on the GSM/EDGE and UMTS/HSPA technologies. It increases the capacity and speed using a different radio interface together with core network improvements. The standard is developed by the 3GPP 3rd Generation Partnership Project and is specified in its Release 8 document series, with minor enhancements described in Release 9. LTE is the upgrade path for carriers with both GSM/UMTS networks and CDMA2000 networks. The different LTE frequencies and bands used in different countries mean that only multi-band phones are able to use LTE in all countries where it is supported.
LTE has been marketed both as "4G LTE" and as "Advanced 4G", but it does not meet the technical criteria of a 4G wireless service, as specified in the 3GPP Release 8 and 9 document series for LTE Advanced. LTE is also commonly known as 3.95G. The requirements were originally set forth by the ITU-R organisation in the IMT Advanced specification. However, due to marketing pressures and the significant advancements that WiMAX, Evolved High Speed Packet Access, and LTE bring to the original 3G technologies, ITU later decided that LTE together with the aforementioned technologies can be called 4G technologies. The LTE Advanced standard formally satisfies the ITU-R requirements to be considered IMT-Advanced. To differentiate LTE Advanced and WiMAX-Advanced from current 4G technologies, ITU has defined them as "True 4G".
LTE stands for Long Term Evolution and is a registered trademark owned by ETSI European Telecommunications Standards Institute for the wireless data communications technology and a development of the GSM/UMTS standards. However, other nations and companies do play an active role in the LTE project. The goal of LTE was 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. A further goal was the redesign and simplification of the network architecture to an IP-based system with significantly reduced transfer latency compared with the 3G architecture. The LTE wireless interface is incompatible with 2G and 3G networks, so that it must be operated on a separate radio spectrum.
LTE was first proposed in 2004 by Japan's NTT Docomo, with studies on the standard officially commenced in 2005. In May 2007, the LTE/SAE Trial Initiative LSTI alliance was founded as a global collaboration between vendors and operators with the goal of verifying and promoting the new standard in order to ensure the global introduction of the technology as quickly as possible. The LTE standard was finalized in December 2008, and the first publicly available LTE service was launched by TeliaSonera in Oslo and Stockholm on December 14, 2009, as a data connection with a USB modem. The LTE services were launched by major North American carriers as well, with the Samsung SCH-r900 being the world's first LTE Mobile phone starting on September 21, 2010, and Samsung Galaxy Indulge being the world's first LTE smartphone starting on February 10, 2011, both offered by MetroPCS, and the HTC ThunderBolt offered by Verizon starting on March 17 being the second LTE smartphone to be sold commercially. In Canada, Rogers Wireless was the first to launch LTE network on July 7, 2011, offering the Sierra Wireless AirCard 313U USB mobile broadband modem, known as the "LTE Rocket stick" then followed closely by mobile devices from both HTC and Samsung. Initially, CDMA operators planned to upgrade to rival standards called UMB and WiMAX, but 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 instead they intend to migrate to LTE. The next version of LTE is LTE Advanced, which was standardized in March 2011. Services are expected to commence in 2013. Additional evolution known as LTE Advanced Pro have been approved in year 2015.
The LTE specification provides downlink peak rates of 300 Mbit/s, uplink peak rates of 75 Mbit/s and QoS provisions permitting a transfer latency of less than 5 ms in the radio access network. 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 IP-based network architecture, called the Evolved Packet Core EPC designed to replace the GPRS Core Network, supports 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-UTRA cell will support up to four times the data and voice capacity supported by HSPA.
Most carriers supporting GSM or HSUPA networks can be expected to upgrade their networks to LTE at some stage. A complete list of commercial contracts can be found at:
The following is a list of top 10 countries/territories by 4G LTE coverage as measured by OpenSignal.com in February/March 2019.
For the complete list of all the countries/territories, see list of countries by 4G LTE penetration.
Long-Term Evolution Time-Division Duplex LTE-TDD, also referred to as TDD LTE, is a 4G telecommunications technology and standard co-developed by an international coalition of companies, including China Mobile, Datang Telecom, Huawei, ZTE, Nokia Solutions and Networks, Qualcomm, Samsung, and ST-Ericsson. It is one of the two mobile data transmission technologies of the Long-Term Evolution LTE technology standard, the other being Long-Term Evolution Frequency-Division Duplex LTE-FDD. While some companies refer to LTE-TDD as "TD-LTE" for familiarity with TD-SCDMA, there is no reference to that acronym anywhere in the 3GPP specifications.
There are two major differences between LTE-TDD and LTE-FDD: how data is uploaded and downloaded, and what frequency spectra the networks are deployed in. While LTE-FDD uses paired frequencies to upload and download data, LTE-TDD uses a single frequency, alternating between uploading and downloading data through time. The ratio between uploads and downloads on a LTE-TDD network can be changed dynamically, depending on whether more data needs to be sent or received. LTE-TDD and LTE-FDD also operate on different frequency bands, with LTE-TDD working better at higher frequencies, and LTE-FDD working better at lower frequencies. Frequencies used for LTE-TDD range from 1850 MHz to 3800 MHz, with several different bands being used. The LTE-TDD spectrum is generally cheaper to access, and has less traffic. Further, the bands for LTE-TDD overlap with those used for WiMAX, which can easily be upgraded to support LTE-TDD.
Despite the differences in how the two types of LTE handle data transmission, LTE-TDD and LTE-FDD share 90 percent of their core technology, making it possible for the same chipsets and networks to use both versions of LTE. A number of companies produce dual-mode chips or mobile devices, including Samsung and Qualcomm, while operators CMHK and Hi3G Access have developed dual-mode networks in Hong Kong and Sweden, respectively.
The creation of LTE-TDD involved a coalition of international companies that worked to develop and test the technology. China Mobile was an early proponent of LTE-TDD, along with other companies like Datang Telecom and Huawei, which worked to deploy LTE-TDD networks, and later developed technology allowing LTE-TDD equipment to operate in white spaces—frequency spectra between broadcast TV stations. Intel also participated in the development, setting up a LTE-TDD interoperability lab with Huawei in China, as well as ST-Ericsson, Nokia, and Nokia Siemens now Nokia Solutions and Networks, which developed LTE-TDD base stations that increased capacity by 80 percent and coverage by 40 percent. Qualcomm also participated, developing the world's first multi-mode chip, combining both LTE-TDD and LTE-FDD, along with HSPA and EV-DO. Accelleran, a Belgian company, has also worked to build small cells for LTE-TDD networks.
Trials of LTE-TDD technology began as early as 2010, with Reliance Industries and Ericsson India conducting field tests of LTE-TDD in India, achieving 80 megabit-per second download speeds and 20 megabit-per-second upload speeds. By 2011, China Mobile began trials of the technology in six cities.
Although initially seen as a technology utilized by only a few countries, including China and India, by 2011 international interest in LTE-TDD had expanded, especially in Asia, in part due to LTE-TDD 's lower cost of deployment compared to LTE-FDD. By the middle of that year, 26 networks around the world were conducting trials of the technology. The Global LTE-TDD Initiative GTI was also started in 2011, with founding partners China Mobile, Bharti Airtel, SoftBank Mobile, Vodafone, Clearwire, Aero2 and E-Plus. In September 2011, Huawei announced it would partner with Polish mobile provider Aero2 to develop a combined LTE-TDD and LTE-FDD network in Poland, and by April 2012, ZTE Corporation had worked to deploy trial or commercial LTE-TDD networks for 33 operators in 19 countries. In late 2012, Qualcomm worked extensively to deploy a commercial LTE-TDD network in India, and partnered with Bharti Airtel and Huawei to develop the first multi-mode LTE-TDD smartphone for India.
In Japan, SoftBank Mobile launched LTE-TDD services in February 2012 under the name Advanced eXtended Global Platform AXGP, and marketed as SoftBank 4G ja. The AXGP band was previously used for Willcom's PHS service, and after PHS was discontinued in 2010 the PHS band was re-purposed for AXGP service.
In the U.S., Clearwire planned to implement LTE-TDD, with chip-maker Qualcomm agreeing to support Clearwire's frequencies on its multi-mode LTE chipsets. With Sprint's acquisition of Clearwire in 2013, the carrier began using these frequencies for LTE service on networks built by Samsung, Alcatel-Lucent, and Nokia.
As of March 2013, 156 commercial 4G LTE networks existed, including 142 LTE-FDD networks and 14 LTE-TDD networks. As of November 2013, the South Korean government planned to allow a fourth wireless carrier in 2014, which would provide LTE-TDD services, and in December 2013, LTE-TDD licenses were granted to China's three mobile operators, allowing commercial deployment of 4G LTE services.
In January 2014, Nokia Solutions and Networks indicated that it had completed a series of tests of voice over LTE VoLTE calls on China Mobile's TD-LTE network. The next month, Nokia Solutions and Networks and Sprint announced that they had demonstrated throughput speeds of 2.6 gigabits per second using a LTE-TDD network, surpassing the previous record of 1.6 gigabits per second.
Much of the LTE standard addresses the upgrading of 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 transitions 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 supports only 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:
One additional approach which is not initiated by operators is the usage of over-the-top content OTT services, using applications like Skype and Google Talk to provide LTE voice service.
Most major backers of LTE preferred and promoted VoLTE 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. VoLTE will also require Single Radio Voice Call Continuity SRVCC in order to be able to smoothly perform a handover to a 3G network in case of poor LTE signal quality.
While the industry has seemingly standardized on VoLTE for the future, the demand for voice calls today has led LTE carriers to introduce 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.
To ensure compatibility, 3GPP demands at least AMR-NB codec narrow band, but the recommended speech codec for VoLTE is Adaptive Multi-Rate Wideband, also known as HD Voice. This codec is mandated in 3GPP networks that support 16 kHz sampling.
Fraunhofer IIS has proposed and demonstrated "Full-HD Voice", an implementation of the AAC-ELD Advanced Audio Coding – Enhanced Low Delay codec for LTE handsets. Where previous cell phone voice codecs only supported frequencies up to 3.5 kHz and upcoming wideband audio services branded as HD Voice up to 7 kHz, Full-HD Voice supports the entire bandwidth range from 20 Hz to 20 kHz. For end-to-end Full-HD Voice calls to succeed, however, both the caller and recipient's handsets, as well as networks, have to support the feature.
The LTE standard covers a range of many different bands, each of which is designated by both a frequency and a band number:
As a result, phones from one country may not work in other countries. Users will need a multi-band capable phone for roaming internationally.
According to the European Telecommunications Standards Institute's ETSI intellectual property rights IPR database, about 50 companies have declared, as of March 2012, holding essential patents covering the LTE standard. The ETSI has made no investigation on the correctness of the declarations however, so that "any analysis of essential LTE patents should take into account more than ETSI declarations." Independent studies have found that about 3.3 to 5 percent of all revenues from handset manufacturers are spent on standard-essential patents. This is less than the combined published rates, due to reduced-rate licensing agreements, such as cross-licensing.