Research On LDPC Codes Encoding Algorithms In Deep Space Communication

Characterized by low SNR and serious loss of information, deep space communication needs excellent channel coding technology to ensure the reliability of information transmission. As a high-gain channel coding technology, low density parity check (LDPC) codes have many advantages, so there are broad prospects to be used in fields of deep space communication. It is a hot spot to be researched how to design suitable LDPC codes for deep space communication.Firstly, the analysis of the methods of constructing parity check matrix and the encoding/decoding algorithms is given, based on the discussion of the LDPC codes' theory. Simulation results show that the RU algorithm can encode the LDPC codes efficiently, and the sum-product algorithm can achieve good error performance, which can be both used in deep space communication.Secondly, a reseach on methods of parity check matrix construction is made according to the characteristics of deep space communication. A new QCE-PEG algorithm is proposed to construct matrix with excellent performance, combining two algorithms adapting to deep space communication. The method can make the average girth as large as possible and the code meeting the degree distribution strictly. The simulation results show that the irregular LDPC codes designed by the proposed algorithm can be encoded efficiently. Furthermore, their performances are superior to the PEG codes', implying good application prospects.Finally, the analysis of the error performance of LDPC codes is made, which shows that the 1/3 rate irregular LDPC codes are more suitable for deep space communication. A scheme is proposed by using QCE-PEG algorithm to construct check matrix, the RU algorithm to efficiently encode the LDPC codes and the sum-product algorithm to decode with good error performance. Then the LDPC-SPC joint coding technique is proposed to further reduce the decoding threshold and the BER-layer, and a scheme suitable for deep space communication is presented, which can satisfy the requirement of BER<10-5 while Eb/N0>0.7 dB.