Error Correction Technology Of The Optical Fiber Communication Based On Repeat-accumulate Codes

Repeat Accumulate (RA) code is a kind of code closed to Shannon limit which follows Turbo code and LDPC code. RA codes have advantages of Turbo code's linear time coding and LDPC code's linear time decoding. In recent years, RA codes have caused widespread attention.RA code mostly uses the sum-product decoding arithmetic which is based on Tanner graph. The RA code's interleaver structure influences the decoding performance. The mostly used interleaver is random interleaver which produces short cycles reducing the RA code's decoding performance. In this paper, combinatorial design is used to construct RA code's two kinds of interleavers which can produce the system regular RA codes which are free of 4-cycles and high code rates. The designed RA codes will be used in long haul optical fiber communication.First of all, Steiner triple system is used to construct system regular RA code's Steiner-interleaver. We construct the incidence matrix of Steiner triple system according to the RA code length. The incidence matrix which is permuted the definite columns can produce the parity-check matrix of RA code. The interleaver sequence can be gained by the parity-check matrix. The Steiner triple system's characteristic determines the designed interleaver is free of 4-cycle. If the code length is determined, the Steiner-interleaver's structure of RA code is also fixed. The Steiner -interleaver structure is steady, the random interleaver structure is random. Compared to the block interleaver, the Steiner-interleaver is free of 4-cycles. If the code length is more long the system regular RA code rate is more close one. Simulation results show that, the system regular RA code based on the Steiner-interleaver has better decoding performance when the RA code is long enough.Secondly, Kirkman triple system is used to construct system regular RA code's KTS-interleaver. The designed Steiner-RA codes which their code rates are all higher. So the Steiner-RA code's application is restricted in the practical communication systems. Transforming the the incidence matrix of Kirkman triple system and choosing the parallel class, we can produce the KTS-interleaver. Kirkman triple system's characteristic promises the designed KTS-RA code is free of 4-cycles. By the choice of parallel class number, we can adjust the check node's degree flexible which produces the RA code's rate range has larger. Simulation results show that, the system regular RA code based on the KTS-interleaver has better decoding performance than the RA code based on the random interleavers.Finally, the system regular RA codes based on combinatorial interleavers are applied in long haul optical fiber communication. The system RA codes based on combinatorial interleavers which are free of 4-cycles and high code rate accord with long laul optical fiber communication's demand of high efficiency and high capability. The system RA codes based on combinatorial interleavers are simulated in optical fiber channels which contain the Chi-square channel, the asymmetric Gaussian channela and AWGN channel. Simulation results show that, the system RA codes based on combinatorial interleavers can get better decoding performance in optical fiber channel. The RA codes'decoding performance is better in Chi-square channel model than Guassian channel model.