Long-Term Evolution Time-Division Duplex
Long-Term Evolution Time-Division Duplex (LTE-TDD), also referred to as Time-division Long-Term Evolution (TD-LTE), is a 4G telecommunications technology and standard co-developed by an international coalition of companies, including China Mobile, Datang Telecom, Huawei, Nokia Solutions and Networks, Qualcomm, Samsung, and ST-Ericsson. It is one of two variants of the Long Term Evolution (LTE) technology standard, the other being Frequency-Division Long-Term Evolution (LTE-FDD).
Overview of technology
Time-Division Duplex LTE, abbreviated as TD-LTE, TDD LTE, or LTE-TDD is one of the two mobile data transmission technologies that fall under the international standard of LTE, the other being Frequency-Division Duplex (LTE-FDD). LTE-TDD was developed specifically with idea of migration to 4G from the third generation 3G TD-SCDMA networks in mind.
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 China Mobile Hong Kong Company Limited and Hi3G Access have developed dual-mode networks in China 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 megabyte-per second download speeds and 20 megabyte-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 FDD network in Poland, and by April of 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 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 of 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 throughput using a LTE-TDD network, surpassing the previous record of 1.6 gigbits per second.
Deployment, commercial networks and devices
As of January 2014[update], there were 28 commercial LTE-TDD networks operating in 21 countries worldwide, with an additional 45 networks planned or in deployment. LTE-TDD deployments are especially popular in Asia and the Pacific, with 47 percent of LTE-TDD contracts awarded to vendors from this region. In second place is the Middle East, with 18 percent of contracts. According to a report conducted by research firm Ovum Ltd. in June of 2012, LTE-TDD connections are expected to make up 25 percent of all LTE connections worldwide by 2016, with operators in Japan, Australia, Saudi Arabia, Sweden, and Denmark having implemented the technology, or planning to in the future.
In 2013, a total of 705 new LTE devices were launched worldwide, of which 304 supported LTE-TDD, up from 180 devices in 2012. By the end of the year, LG, Samsung, and Nokia had all demonstrated devices which support LTE-TDD, or indicated that they plan to launch devices that support the technology in the future. Apple also introduced iPhone 5S and 5C models that support both LTE-TDD and LTE-FDD.Beginning January 6th 2015, Apple also began selling a SIM-free iPhone 6 / 6 plus that supported 4 LTE-TDD bands (38, 39, 40, 41), corresponding to TD2600, TD1900, TD2300, and TD2500.
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