A practical approach toward maximum likelihood sequence estimation for band-limited nonlinear channels

A receiver structure referred to as a pseudo maximum likelihood sequence estimation (pseudo MLSE) that approximates MLSE with a simple hardware configuration is derived. By introducing a tentatively estimated sequence, the pseudo MLSE detects the received sequence symbol by symbol, thereby retaining the MLSE optimum decision property. The required number of arithmetic operations for one symbol duration is reduced from M to the (L + 1) power to (L + 1)M in an M-ary signaling case with a channel memory length L. An adaptation algorithm for the variation in the channel characteristic is also developed. A description is given of pseudo MLSE application to quadrature phase shift keying for a band-limited nonlinear channel. The most practical application of pseudo MSLE, referred to as the adaptive threshold detector with estimated sequence (ATDES), detects symbols with threshold detection and is suitable for high bit rate operation.