A new n/m code and modified viterbi decoding in magnetooptical recording

Abstract

AbstractThis paper proposes the (4, 5, 6)/11 code, which is a new n/m code, constrained in that the minimum runlength of symbol “O” in the codeword is 2 and is suited to PR(1, 1) equalization. In PR(1) equalization, a pseudo‐PR(1, 1) characteristic is obtained by shifting the sampling points by Ts/2 (where Ts is the symbol interval). Assuming that the conventional Viterbi decoding is applied to the (4, 5, 6)/11 code, the error‐rate characteristic is examined by simulation, and the result is compared to that of the well‐known 4/11 code. It is shown as a result that the (4, 5, 6)/11 code has an excellent performance. Then a modified Viterbi decoding is considered by utilizing the run‐length constraint, and the performance is evaluated.The colored noise sequence is approximated by a simple Markov process and another modified Viterbi decoding utilizing the correlation of the noise sequence also is considered. It is shown as a result that the CN ratio is improved compared to the conventional Viterbi decoding by about 1.0 dB in the former and about 2.7 dB in the latter, at the error rate of 10−4.