Construction And Implementation Of Rate Compatibility QC-LDPC Codes Based On Protograph In Satellite Laser Communication

With the development of space technology,laser communication plays an increasingly important role in global communication due to its advantages such as high speed,large communication capacity and strong anti-interference ability.In the inter-satellite laser communication,the distance between satellites varies frequently,and it also affected by the sunlight,electromagnetic particles and other factors.The reliability of inter-satellite laser communication can be improved by using channel coding technology.Among many channel coding methods,LDPC codes has been widely used because of its advantages such as close to Shannon limit performance,low coding complexity and easy hardware implementation.The rate-compatible QC-LDPC codes constructed based on the AR4 JA protograph in this thesis not only has the advantages of high speed decoding,low decoding threshold and low error floor of the protograph LDPC codes,but also has the advantages of rate-compatible,which can adjust the encoding method according to the current channel state and improve the information transmission rate of the communication system.The main research work includes:1.In view of the traditional protograph expansion algorithm,only the candidate node with the smallest degree is selected in the first expansion,and it does not consider how to improve the connectivity of the cycle when there is a cycle in the first expansion.The constructed LDPC codes will have a large number of short cycles and other problems resulting in poor decoding performance,In this thesis,we propose an optimized protograph PEG algorithm.The algorithm using PEG to eliminate multiple edges and construct cyclic shift matrix,the concrete methods based on PEG structure in the process of adding the characteristics of the edge to maximize the local girth,when add edge not form a cycle,will assign a random permutation shift,when there is a cycle,the candidate nodes larger than ACE threshold are selected and utilizing the cycle existence theorem to eliminate existing cycles.The proposed algorithm is used to extend the AR4 JA protograph,and construct the LDPC codes with the same length and rate as the CCSDS deep space communication standard.The simulation results show that the codes constructed by the proposed algorithm do not contain short cycles and the minimum girth is 6,also it have great error correction performance.2.Rate-compatible encoding and decoding of OP-PEG(2048,1024),OP-PEG(1536,1024)and OP-PEG(1280,1024)codes with information bit length of 1024 and codes rate of 1/2,2/3 and 4/5 are implemented on FPGA.The rate-compatible technology can choose the encoding mode according to different channels,which ensures the communication reliability and improves the information transmission rate.It has a great application prospect in satellite laser communication.The Belief Propagation algorithm and the Normalized Minimum Sum algorithm are simulated for the three codes,and the normalization factor,the number of iterations and the quantization bit width are determined.The hardware realized the encoding throughput of 200 Mbps and the decoding throughput of 36.35Mbps?136.53Mbps.