Performance comparison of imperfect symbol- and bit-interleaving of block codes over GF(2m) on a Markovian channel

We analytically compare the performance of imperfectly symbol- and bit-interleaved block codes over GF(2^m) on a first-order Markovian channel in terms of the error probability of a received word. The analytical method developed in Sakakibara (2000) is extended, so that binary transmission of block codes over GF(2^m) can be incorporated with the assumption of negligible probabilities of decoding error. Expressions are derived for two decoding strategies; independent bounded-distance (IBD) decoding and error-forecasting (EF) decoding. In the IBD decoding, channel errors up to half of the minimum distance can be decoded in each received word. On the other hand, combining an erasures-and-errors decoding algorithm, more errors may be corrected in the EF decoding. The derived expressions are examined on two typical classes of two-state Markovian channels. Numerical results indicate that a combination of symbol-interleaving and the EF decoding offers the best performance even for imperfect interleaving. This can compensate for the superiority of perfect symbol-interleaving to perfect bit-interleaving addressed by Wicker (1992). It is also found that the optimum depths of symbol- and bit-interleaver is approximately given by 2b and 4b, respectively, where b is the average length of burst errors in bits.