Digital echo suppressor for MODEM - generates number for each symbol applied to set of filters whose outputs minimise echo (BE 17.7.78)

摘要

The modem is for data transmission by modulation of a carrier with symbols derived from the binary data to be transmitted. Modem sender and receiver are connected to the transmission line through a hybrid circuit. The echo suppressor receives the binary data to be transmitted and delivers an echo copy signal which adaptively reduces an error signal, the difference between the received signal and the echo copy signal. The echo suppressor has circuitry to generate, in response to each symbol, at least one number, a function of the carrier amplitude at the instant of its appearance. This number is applied to a certain part of a system of digital adaptive filters whose output signals are combined to produce a digital form of the echo copy signal. Coefficients of these filters are adjusted by a set of circuits which receive the above error signal and minimise it.