China unveils their own 3G standard, time-division synchronous code, division multiple access, or TD-SCDMA in time for the Summer Olympics. Trial network evaluations throughout 2007 have culminated in a Beijing-centric commercial rollout.

TD-SCDMA represents China's efforts to reduce dependence on Western technology for next-generation cellular communications, although in fact that effort can be claimed only partially successful in the Hisense T68 Mobile Phone deconstructed here. By developing TD-SCDMA, China hopes to bypass much of the royalty stream associated with wideband-CDMA, the more broadly deployed global 3G protocol. That said, the presence of the "CDMA" in the standard's protocol designation tips the use of spread-spectrum communications at some level, so perhaps the intellectual-property issues and costs will not fully be dodged.

TD-SCDMA implements a hybrid of time-division (the TD part) and frequency-division multiple access in an effort to get the benefits of dynamically allocated time slots for downlink and uplink, to support varying traffic asymmetry. Additionally, the downlink and uplink traffic can be multiplexed onto the same carrier frequency (vs. needing paired spectrum), resulting in more flexibility in channel allocation.

Within a time slot, communications use a synchronized CDMA technique. The scheme improves spectral efficiency, since multiple users can share the same channel as long as their chipping codes are suitably different to allow isolation of the distinct traffic within the common slice of spectrum.

The first examples of TD-SCDMA hardware also support legacy GSM communications as a link to the past, just as UMTS combines GSM and W-CDMA elsewhere to allow more-seamless use of old and new.

By: DocMemory
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