Performance of systematic RA code in long haul optical fiber communication system

The systematic repeat-accumulate (RA) code is constituted by a repeater, an interleaver, a combiner and an accumulator. Under the sum-product decoding on the Tanner graph of the code, the performance of RA codes with random interleaver is affected by short cycles of parity-check matrix. In this paper, we present combinatorial design of interleaver. The RA code with new interleaver can produce very high code rate and its parity-check matrix is free of 4-cycles. Thus the codes are likely to be used in long haul optical fiber communication system. We analyze the performance of the systematic RA code in three optical fiber transmission models. Simulation results show that RA codes with combinatorial interleaver have better performance than that of the code with random interleaver in fiber communication system. The decoder based on Chi-square also has better performance than of the decoder based on Gaussian models.