Study On The Techniques Of Channel Coding In High Rate Passive Optical Networks

Due to its low cost,high bandwidth and stable performance,the Passive Optical Network(PON)has become one of the main optical access techniques.With the increase of the rate of PON system,the use of coding gain higher forward error correction(FEC)coding is needed to improve the power budget.The quasi cyclic low density parity check(QC-LDPC)code is a kind of forward error correction encoding with high gain and parallel encoding and decoding,which is widely studied in the field of optical communication and channel encoding.Compared with single and fixed rate FEC in the traditional PON system,adaptive FEC makes full use of the different signal to noise ratio(SNR)of the ONU(caused by the difference of transmission distance and the device)to design different rate of FEC,which can effectively improve the system bandwidth utilization.In this paper,the QC-LDPC coding and adaptive FEC scheme system for high speed PON system are studied and designed.The main research work is summarized as follows.1.To providing the basis for the design of resource reusable decoder in the adaptive FEC scheme,and the excellent error correction performance,a kind of multi rate QC-LDPC code construction method based on finite geometry construction method combined with masking matrix is designed.The parity check matrix of a set of QC-LDPC codes with inheritance relation and excellent error correction performance is obtained.Simulation results under BPSK modulation and AWGN channel show that,the error correction performance from the Shannon limit is less than 1dB when the rate range of multi rate QC-LDPC codes constructed is 0.8-0.92.2.For the needs of multi-rate encoding in rate adaptation QC-LDPC encoder and coding delay caused by the large length of shift register,a kind of low latency rate adaptation QC-LDPC encoder is designed.By the parity packets of shift register structure,the Shift Register Adder Accumulator(SRAA)structure reduce the coding delay;By the initialization of low latency SRAA array through ROM which the generating polynomial is stored,the encoding for different code rate can be realized.The correctness of the encoder scheme is verified by the rate adaptive QC-LDPC encoding simulation.3.For the needs of multi-rate decoding in rate adaptation QC-LDPC decoder and the simplification of decoding structure,a kind of rate adaptive QC-LDPC decoder is designed which is based on the node rearrangement and dynamic check nodes unit.The complexity of the permutation network is reduced by the variable node rearrangement.The reuse of the permutation network is realized by the dynamic calibration node.Through the code rate adaptive QC-LDPC decoding simulation,the correctness of the scheme is verified.4.The code rate of all the ONU is single and fixed according to the traditional PON system based on the worst SNR,and the FEC overhead for the ONU of the non-worst SNR is wasteful.To solve this problem,an adaptive FEC scheme with different code rates is designed according to the different ONU SNR.This scheme uses the different rates of codewords for the ONU according to the SNR respectively,which can effectively improve the system bandwidth utilization.The simulation results of 10G PON system show that the design scheme can effectively improve the system capacity.When the ONU SNR is evenly distributed,the system capacity can be promoted by 40%.