TD-SCDMA

Time Division-Synchronous Code Division Multiple Access, or TD-SCDMA, is a 3G mobile telecommunications standard, being pursued in the People's Republic of China by the Chinese Academy of Telecommunications Technology (CATT), Datang and Siemens AG, in an attempt not to be "dependent on Western technology" This is likely primarily for practical reasons, other 3G formats require the payment of patent fees to a large number of western patent holders [ [http://www.3glicensing.com/articles/News%20LowCost.pdf "3G Licensing introduces the W-CDMA Patent Licensing Programme at the "Low Cost 3G Devices" conference"] , London, 13 March 2007] . TD-SCDMA is based on spread spectrum technology which makes it unlikely that it will be able to escape completely the payment of license fees to western patent holders. The launch of a national TD-SCDMA network was initially projected by 2005 [ [http://www.eetasia.com/ART_8800451183_499488_67aa06a5200701_no.HTM "3G in China still held up"] , EE Times Asia, Global Sources] but has still not been achieved; the latest stage of "commercial trials" across eight cities was launched on April 1, 2008 and will eventually include 60,000 users [ [http://www.cellular-news.com/story/30163.php "China Mobile to Test Td-scdma on 60,000 Phones from April 1"] , Cellular News] .

Deployment and Usage

On January 20, 2006, Ministry of Information Industry of the People's Republic of China formally announced that TD-SCDMA is the country's standard of 3G mobile telecommunication. On February 15, 2006, a timeline for deployment of the network in China was announced, stating pre-commercial trials would take place starting after completion of a number of test networks in select cities. These trials ran from March to October, 2006, but the results were apparently unsatisfactory. In early 2007, the Chinese government instructed the dominant cellular carrier, China Mobile, to build commercial trial networks in eight cities, and the two fixed-line carriers, China Telecom and China Netcom, to build one each in two other cities. Construction of these trial networks was scheduled to finish during the fourth quarter of 2007, but delays meant that construction was not complete until early 2008.

The standard has been adopted by 3GPP since Rel-4, known as "UTRA TDD 1.28Mcps Option". This, and TD-CDMA (an independently developed TDD CDMA system more closely related to W-CDMA), are offered as air interfaces for the UMTS-TDD system, a version of UMTS used largely to provide Internet access. The use of TDD is more efficient than FDD at dynamically providing asymmetric data rates, which are typical in ordinary Internet use.

On March 28, 2008, China Mobile Group announced TD-SCDMA will start operating "commercial trials" for 60,000 test users in eight cities from April 1. Networks using other 3G standards (WCDMA and CDMA2000 EV/DO) have still not been launched in China, as these will be delayed until TD-SCDMA is ready.

Technical highlights

TD-SCDMA uses TDD, in contrast to the FDD scheme used by W-CDMA. By dynamically adjusting the number of timeslots used for downlink and uplink, the system can more easily accommodate asymmetric traffic with different data rate requirements on downlink and uplink than FDD schemes. Since it does not require paired spectrum for downlink and uplink, spectrum allocation flexibility is also increased. Also, using the same carrier frequency for uplink and downlink means that the channel condition is the same on both directions, and the base station can deduce the downlink channel information from uplink channel estimates, which is helpful to the application of beamforming techniques.

TD-SCDMA also uses TDMA in addition to the CDMA used in WCDMA. This reduces the number of users in each timeslot, which reduces the implementation complexity of multiuser detection and beamforming schemes, but the non-continuous transmission also reduces coverage (because of the higher peak power needed), mobility (because of lower power control frequency) and complicates radio resource management algorithms.

The "S" in TD-SCDMA stands for "synchronous", which means that uplink signals are synchronized at the base station receiver, achieved by continuous timing adjustments. This reduces the interference between users of the same timeslot using different codes by improving the orthogonality between the codes, therefore increasing system capacity, at the cost of some hardware complexity in achieving uplink synchronization.

References

ee also

* Dynamic TDMA
* Telecommunications industry in China
* Communications in China

External links

* [http://www.tdscdma-forum.org/EN/index.asp TD-SCDMA Forum]
* [http://www.tdscdma-alliance.org/english/ TD-SCDMA Industry Alliance]
* [http://www.forbes.com/home/feeds/afx/2006/12/10/afx3243150.html China will not interfere in 3G standard selection]
* [http://www.china.org.cn/english/news/187783.htm China will provide 3G Service] in cities where Olympic Games 2008 are held