Linear echo cancellation using optimized recursive prefiltering

In order to reduce the circuit complexity associated with the estimation of echos coming from systems with long impulse responses, an estimation is considered which is based on prefiltered input data. The design of a prefilter which is optimal for a given system environment is proposed. In doing so, the unknown discrete-time system is represented by a set of characteristic unit-sample responses which adequately describe the variation of the system. For such an environment, the optimal poles of a recursive prefilter are determined, and an orthogonal realization is suggested. These poles are assumed to be fixed during the on-line estimation process, which estimates the unknown system output by linearly weighting a set of optimally prefiltered input data. A 70-dB echo canceller for the North American Telephone subscriber loop environment is used as an example