Single-chip link offers alternative

Electronics Times, May 8, 2000

Infineon Technologies has developed a single chip for the next generation of standard high-speed symmetrical telecoms link that it thinks could be an alternative to ADSL roll-outs.

The symmetric high bitrate digital subscriber loop (SHDSL) standard brings together proprietary HDSL and SDSL approaches in a single standard, approved by the International Telecommunications Union three weeks ago. The G.shdsl standard allows symmetrical data rates of up to 2.3Mbit/s over distances of 2.4 or 4.5km for 384Kbit/s over a single twisted pair.

This is significantly further than ADSL or HDSL systems today, and means SHDSL could be used for a business version of ADSL as it does not need a splitter in the central office or the home but does need a new network termination box. It may also be easier to manage as an individual line can be tested from the exchange, not possible with current ADSL systems.

The other claimed advantage of G.shdsl is that it uses a coding scheme to fit into the spectrum of the telecoms network, unlike other HDSL and SDSL solutions based on 2B1Q coding used for leased lines and ISDN. It includes 2B1Q capability for backwards compatibility.

The trellis-coded pulse amplitude modulation scheme provides a coding gain of around 5dB and uses a simpler Viterbi decoder to regain the original information. But the scheme is totally different to the DMT coding used for ADSL.

This, along with a relatively low 1W power consumption, will make it appeal to telecoms operators, says Christian Wolff, vice-president and general manager of Infineon's transceiver business unit.

The SDHSL one-chip rate adaptive transceiver with embedded start-up chip was developed with Adtran in the US. It includes the analogue front-end, line driver, DSP datapump and a rom-based 8032-type controller on a hybrid substrate.