Matched spectral-null codes with soft-decision outputs

Considers the concatenation of an inner matched-spectral-null (MSN) code with an outer error-correcting code to achieve improved performance on a partial-response channel in the presence of additive white Gaussian noise. The authors show how to modify the reduced-complexity Viterbi algorithm of Karabed and Siegel [1991] to produce reliability values for each bit using the procedure proposed by Hagenauer and Hoeher [1989]. These reliability values are then used by the outer decoder to achieve improved performance. The authors simulated a number of codes and observed improvements due to soft-decision decoding of 1-2 db.<>