Research And Implementation Of Decoding Algorithms For LDPC Codes With Multiple Rates And Multiple Block-sizes

It has been proved that low density parity check(LDPC)code is the closest code to Shannon's performance limit.The sparseness of check matrix in LDPC code makes the computational complexity greatly reduced in hardware implementation.LDPC code has been widely used in communication systems,such as wireless local area networks(WLAN),mobile communication system,satellite communications,deep space exploration,and satellite digital video broadcasting and so on.The consultative committee for space data systems(CCSDS)proposed LDPC Codes with multiple rates and variable block-sizes for the characteristics of long distance communication,long data frames,large space propagation loss,low received SNR,and wider available channel bandwidth for aerospace telemetry links.The paper focuses on the decoding algorithm of LDPC code recommended by CCSDS,and the key research focuses on the decoding algorithm and hardware implementation of LDPC codes with multiple rates and variable block-sizes.The mainly contents are as follows:(1)The basic principle of LDPC code is introduced,and two commonly used decoding methods for LDPC codes are mainly studied,telemetry LDPC codes recommended by CCSDS are introduced at the same time.(2)A layered offset min-sum algorithm(LOMS)suitable for CCSDS telemetry link has been proposed aiming at the problems of long LDPC codes,large amount of decoding calculation,and slow convergence of conventional decoding in CCSDS telemetry link LDPC codes.The algorithm improves the decoding performance by stratifying the check matrices of LDPC codes,and subtracting a certain offset to compensate for the overestimated information amplitude in the min-sum algorithm and transferring information between layers in time.The analysis and simulation results show that the decoding complexity of the LOMS algorithm is much smaller than that of the ideal LLR BP decoding algorithm.The decoding convergence speed of the former is twice that of the latter,and the decoding performance is only about 0.1 dB loss.(3)A decoding structure based on layered offset min-sum decoding algorithm has been designed aiming at CCSDS telemetry link LDPC codes,the decoding structure reduces iterations by introducing layer process on the basis of partial parallel decoding structure,and detailed schemes of information storage,data selection,subtractor,check node processing,variable node processing and decoding timing control are given.(4)The decoder is implemented on the FPGA,and the resource consumption of the decoder is analyzed.A test platform is set up to test the actual performance of the decoder.The test results show that the actual performance of the designed layered decoder is very close to the simulation results,and the result demonstrates that the designed decoder is feasible and correct.