Just in time for the world stage of the 2008 Beijing Summer Olympics, China's own 3G standard--time-division synchronous code-division multiple access, or TD-SCDMA--is at the starting gate. 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 (the CDMA part) 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.

One such dual-mode GSM-TD-SCDMA handset is the Hisense T68. The phone is a bar-style handset, keeping assembly complexity fairly low. An internal frame supports the circuit boards, display and battery, while a single front shell and two-piece back shell supply decorative fascia. Most of the electronics reside on a single circuit board that runs the length of the phone. But a separate keypad board is used, in part because the electronics leave limited room for an in-built keyboard array once "dead space" for the display clearance is allocated. The display itself is a TFT LCD from Lead Communications (Shenzhen, China) measuring 2.4 inches on the diagonal, overlaid here with a resistive touchscreen.

Looking at the primary circuit board, the name Analog Devices hits like a ton of bricks. Despite the China-driven origin of TD-SCDMA, it seems the Norwood, Mass., company is the semiconductor force in rendering the standard to silicon here--or was. In late 2007, Analog Devices sold its cellular chip set to Taiwan's Mediatek for $350 million, so these are legacy components, albeit a recent legacy. In fact, date codes suggest a late September or early October manufacture, timed about even with the Mediatek acquisition. So we'll refer to the devices as Mediatek's, despite the outward branding.

Source:EE Times