Design And Implementation Of LDPC Encoder And Decoder

LDPC codes in deep space communication has very good practical value, at thesame time, the LDPC code has been widely used in optical fiber communication,satellite digital video and audio broadcasting. in additive white Gauss noise channelenvironment, BPSK modulation, normalized min sum decoding algorithm can wellbalance the decoding performance and algorithm complexity degree, can be easilyimplemented in hardware, and often appears in the form of pipeline in decoderdesign. A new method to design LDPC decoder is proposed.The idea of pipeline isabstracted from decoding algorithm itself and applied into the overall decoderdesign.Based on this method a simple decoder which can process multiple framesparallelly is presented,and its performance is tested by simulation andimplementation in the end.In this paper, the main research work is as follows:Firstly, double recursive pipeline encoder is designed using the features ofdouble diagonal QC-LDPC code check matrix. The structure of this encoder and itscoding principle is well presented.The work flow of this encoder is well analysed.And its timing simulation diagram and resources consumption is given.Secondly, the probability domain BP algorithm, the logarithm domain BPalgorithm and the normalized min sum algorithm were respectively introducedaccording to the evolution process of decoding algorithm of LDPC code, and theirperformances are simulated and compared. Then the influence to decodingperformance caused by normalizing coefficient, times of iterations and quantizationbits of initial values is simulated, and appropriate choices are maded according tothe simulation result.After that, the idea of pipeline decoder is proposed. The pipelining method ofthe normalized min sum decoding algorithm is given. The structure and workingprinciple of the pipeline decoder is well introduced.Two kinds of decoder aredesigned based on normal and quasi cyclic LDPC codes. Their simulation resultsand further optimization direction are given.Finally, two sets of encoder and decoder are implemented on a FPGAboard.With the help of softwares like Matlab and serialport assistant, two sets ofencoding and decoding systems, which can do real encoding and decoding work, are set up in cooperation with a computer using serialport. Finally, the performance ofthe encoders and decoders in practical applications are tested.