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TI Bets Chips on Advanced TDMA

Texas Instruments Inc. last week unveiled an advanced Time Division Multiple Access (TDMA) system based on silicon that the company claims can boost the cable upstream path by 50 percent.

By giving the upstream a more symmetrical relationship with the downstream, the technology could pave the way for such nascent cable-based services as videoconferencing and peer-to-peer networking.

While a typical downstream supports speeds of 30 to 40 megabits per second, today's much skinnier upstream pipe typically handles payloads of between five and 10 mbps, explained Eric Dewannian, general manager of TI's cable-broadband division. With the addition of advanced TDMA, he said, the return path could support 30 mbps, closely mirroring the 64 QAM (quadrature-amplitude modulation) operators typically harness in the downstream at present.

TI plans to add the TDMA feature to its customer-premise chip, the TNETC4042, which was introduced last November, as well as its new TNETC4522 dual-channel receiver, which is designed for use inside cable-operator headends.

Cable Television Laboratories Inc. has already certified a number of 4042-outfitted cable modems for Data Over Cable Service Interface Specification (DOCSIS) 1.0. TI declined to say which vendors are using the chip.

But both of those devices support Increased Capacity Ingress Cancellation (INCA), a proprietary noise-cleaning technology TI acquired in its 1999 acquisition of Libit Signal Processing Ltd.

INCA's true benefits are found in how it mitigates ingress, or the noise that coax picks up from electrical appliances and other devices, Dewannian said. Test results have shown INCA to reduce noise immunity by at least 30 percent even in the most hostile plant environments, Dewannian noted.

He added that both chips are available today in sample quantities. Full-scale production will ramp up sometime in the third quarter, he said.

Of course, TI isn't the only company spending time and money on advanced PHY, which is being touted as an enhancement to DOCSIS 1.1. Broadcom Corp. and Conexant Systems Inc. also are exploring advanced PHY based on TDMA. Additionally, Terayon Communications Systems Inc. is pushing S-CDMA (synchronous code division multiple access), a proprietary modulation scheme.

CableLabs, meanwhile, has revitalized its work on advanced physical-layer technology but has yet to bestow its full endorsement on any of those approaches.

In a briefing with reporters earlier this year, CableLabs said it plans to complete a specification for advanced PHY by the end of third-quarter 2001.