Performance comparison of combined ECC/RLL codes

The authors present a comparison of several combined error-correcting/run-length-limited codes created by concatenating a convolutional code with a run-length-limited code. Encoding and decoding are accomplished using a single trellis based on the combined code. Half of the codes under investigation use conventional (d,k) run-length-limited codes, where d is the minimum and k is the maximum allowable run of 0s between 1s. The other half use a special class of distance-preserving codes which have the property that the pairwise Hamming distances out of the ( d,k) encoder are at least as large as the corresponding distances into the encoder. Thus a combined code, created using a convolutional code concatenated with a distance-preserving (d,k) code, will have a free distance no smaller than that of the original convolutional code. A computer simulation compares the performance of these two types of codes over the binary symmetric channel for various (d,k) constraints, rates, free distances, and numbers of states. Of particular interest for magnetic recording applications ar codes with run-length constraints (1,3), (1,7), and (2,7)