An Echo-Cancellation-Based 4800 Bit/s Full-Duplex DDD Modem

In this paper we describe an experimental 4800 bit/s fullduplex DDD modem which has been constructed at Bell Laboratories and AT&T Information Systems. The modem achieves full-duplex operation by using echo cancellation techniques. The main features of the modem´s architecture and start-up procedure are discussed in the paper. We also study in detail the characteristics of an echo canceller structure which was found to be particularly attractive for this application. Finally, we present experimental performance results obtained over simulated channels in the laboratory and over telephone loopback facilities.