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Time Division Synchronous Code Division Multiple Access (TD-SCDMA) or UTRA TDD 1.28 mcps low chip rate (UTRA-TDD LCR) is an air interface〔 found in UMTS mobile telecommunications networks in China as an alternative to W-CDMA. The term "TD-SCDMA" is misleading. While it suggests covering only a channel access method, it is actually the common name for the whole air interface specification.〔 Together with TD-CDMA, it is one of the two time-division duplex (TDD) UMTS air interfaces (UTRAs), known commonly as UMTS-TDD or more formally as IMT-2000 CDMA-TDD or IMT 2000 Time-Division (IMT-TD).〔 Both air interfaces use a combination of two channel access methods, code division multiple access (CDMA) and time division multiple access (TDMA): the frequency band is divided into time slots (TDMA), which are further divided into channels using CDMA spreading codes. These air interfaces are classified as TDD, because time slots can be allocated to either uplink or downlink traffic. TD-SCDMA / UMTS-TDD (LCR) networks are incompatible with W-CDMA / UMTS-FDD and TD-CDMA / UMTS-TDD (HCR) networks. == Objectives == TD-SCDMA was developed in the People's Republic of China by the Chinese Academy of Telecommunications Technology (CATT), Datang Telecom, and Siemens AG in an attempt to avoid dependence on Western technology. This is likely primarily for practical reasons, since other 3G formats require the payment of patent fees to a large number of Western patent holders.〔(''3G Licensing introduces the W-CDMA Patent Licensing Programme at the "Low Cost 3G Devices" conference'' ), London, March 13, 2007〕 TD-SCDMA proponents also claim it is better suited for densely populated areas.〔 Further, it is supposed to cover all usage scenarios, whereas W-CDMA is optimised for symmetric traffic and macro cells, while TD-CDMA is best used in low mobility scenarios within micro or pico cells.〔 TD-SCDMA is based on spread spectrum technology which makes it unlikely that it will be able to completely escape the payment of license fees to western patent holders. The launch of a national TD-SCDMA network was initially projected by 2005〔(''3G in China still held up'' ), EE Times Asia, Global Sources〕 but only reached large scale commercial trials with 60,000 users across eight cities in 2008.〔(''China Mobile to Test Td-scdma on 60,000 Phones from April 1,'' ), Cellular News〕 On January 7, 2009, China granted a TD-SCDMA 3G licence to China Mobile.〔(''China issues 3G licences to main carriers'' ) The Reuters UK〕 On September 21, 2009, China Mobile officially announced that it had 1,327,000 TD-SCDMA subscribers as of the end of August, 2009.〔()〕 While TD is primarily a China-only system, it may well be exported to developing countries. It is likely to be replaced with a newer TD-LTE system over the next 5 years. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「TD-SCDMA」の詳細全文を読む スポンサード リンク
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