Matched spectral-null codes with soft-decision outputs

The concatenation of an inner matched-spectral-null (MSN) code with an outer error-correcting code is considered to achieve improved performance on a partial-response channel in the presence of additive white Gaussian noise. It is shown 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. An inner MSN and an outer convolutional code are simulated. An improvement of about 1.7 dB over the same code using hard-decision decoding of the inner code is observed