Baseband trellis coded modulation with combined equalization/decoding for high bit rate digital subscriber loops

摘要

Presents a simulation-based study evaluating the performance of trellis-coded modulation with combined code/ISI (intersymbol interference) sequence estimation for high-bit-rate (800-kb/s) transmission on subscriber loops. The receiver contains the fractionally spaced forward filter of a decision feedback equalizer as a front end; this is shown to suppress phase-synchronized crosstalk very effectively. It is observed that trellis codes with large numbers of states are needed to obtain reasonable coding gain on a channel with severe ISI, such as a DSL (digital subscriber loop). Coded modulation along with a reduced-complexity sequence estimator (combined equalization and decoding with fewer states) can improve the transmission range of the high-bit-rate DSL system. The results indicate that achieving high-bit-rate transmission on the worst case CSA (carrier serving area) loops with 12-dB noise margin under stationary interference conditions is not possible, while loops longer than the CSA limit can be covered under cyclostationary interference.