A reduced-complexity sequence detector with soft outputs for partial-response channels

Data transmission in a partial-response channel in the presence of additive white Gaussian noise is often accomplished using a concatenated code consisting of an inner modulation code and an outer error-correcting code. We propose a decoder for such a code consisting of an inner reduced-complexity sequence decoder (RCSD) matched to the channel followed by an outer ECC decoder. The inner decoder we propose is essentially that of Simmons (1990), modified to provide not only the most likely data sequence but also an estimate of the reliability of each bit. These reliability values are then used by the outer decoder to achieve improved performance. We introduce a simplified method of computing the reliability values, and we demonstrate by simulation that our decoder often works as well as a more complicated procedure described previously