DIGITAL DUPLEX COMMUNICATION SYSTEM

摘要

A digital duplex communication system for data signals having a power-versus-frequency spectrum having two side bands located one each side of a symbol frequency, the system comprising a transmitter/receiver which includes an echo canceller. The received signal is sampled at a multiple of the bit rate and has in each symbol period a first time during which data is valid (true eye) and a second time during which data is invalid (false eye). The receiver includes circuitry to decode the data from the sampled signal during the true eye. The echo canceller is designed to be operative only during the sampling instant in the true eye and at one of the zero crossing instants in each bit period. Thus the echo canceller is operative at the instants t1 and t2 but not at the instants t3 and t4 when no information is being extracted from the received signal. This enables the storage capacity of a look-up table type echo canceller to be reduced and the processing speed of a transversal filter type echo canceller to be reduced.