Linear echo cancellation using optimized orthogonal recursive filters

In order to reduce the circuit complexity associated with the estimation of echoes coming from systems with long impulse responses, estimation based on orthogonal prefiltered input data, is considered. A design of this prefilter that is optimal for a given system environment is proposed. The unknown discrete-time system is represented by a set of characteristic unit-sample responses, which adequately describe the variation of the system. A flexible orthogonal filter based on the inverse lattice filter is introduced, and how to optimize its poles is discussed. The obtained poles are fixed during the online estimation process, which estimates the unknown system output by linearly weighting a set of optimally prefiltered input data. A 70-dB echo canceler for the North American telephone subscriber loop environment is used as an example