Research On LDPC Enconding And Decoding Technology Based On FPGA

Space optical communication has a series of advantages including strong resistance to electromagnetic interference, narrow beam, good directivity, wide band, low cost,it gets people’s attention increasingly.But the system performance of the space optical communication is easily affected by weather conditions and environmental noise factors, then increases the ber of communication system.It may greatly constrained the development and application of space optical communication technology.Channel coding technology can effectively reduce bit error rate of the system.In the field of error control coding,the low density parity check code (LDPC) is a very good code and the performance is very close to the Shannon limit (Shannon). The LDPC has the advantages such as the relationship between code length and decoding complexity is linear, the low hardware implementation complexity, high rate of decoding ability,and it has become the first selection of error control coding.In this thesis, the space optical communication technology and the error control coding technology have a organic combination. In full consideration of the atmosphere random channel characteristics of PPM modulation in space optical communication system and the advantages of LDPC codes,using the development of FPGA hardware design technology,the thesis studies the application of LDPC code decoding technology in the space optical communication system based on FPGA.Firstly, this thesis studies the theory of LDPC codes, mainly including the definition of LDPC codes, representation, the structure of the check matrix and coding and decoding principle,at the same time having a simple introduction of th principle of space optical communication system.Secondly,it has an analysisi and comparison of hard decision decoding algorithm and the soft decision decoding algorithm,and has the simulation analysis of the performance of the different decoding algorithms.The results show that choosing a suitable weave decoding scheme is necessary to consider the relationship between performance and complexity of hardware implementation.Thirdly,it puts foward technology solutions of PI rotating LDPC code decoding technology used in space optical communication system,and uses the Matlab software to have system modeling and performance simulation analysis of space optical communication system using PPM modulation. Results show that in atmospheric channel based on PPM modulation, system error correction performance is significantly improved using the rotary code of PI after coding and decoding technical scheme.Finally,the paper completed PI rotating LDPC code encoder,decoder design and its implementation based on the FPGA hardware development platform, using the Quartus Ⅱ9.1software design tools,Verilog DHL language, and verified the results by Modelsim6.5software.