Echo canceller design and implementation of a CCITT V32 modem: software solution

The authors describe a software solution for echo cancellation in a full-duplex two-wire high-speed modem. A PLL (phase-lock loop) structure consisting of a second-order low-pass filter implemented in multiprecision arithmetic for both half- and full-duplex operation is used. Combined with the far-end echo canceller, it produces a very reliable alternative capable of tracking up to 10-Hz frequency offset affecting the first remote echo. The digital signal processing was obtained by using the ADSP 2100. Some tests have been made with two V32-based modems between Belgium and the United Kingdom, between Belgium and Sweden, and within Belgium. Some results are shown on the echo cancellation performance as well as the type of transmission lines and impairments affecting them.<>