Research And FPGA Design On Soft-spread Spectrum Signal’s Soft-decision Decoding Algorithms For LDPC Codes

Low Density Parity Check(LDPC) codes is discovered to be one of the best performance of the error correction coding technique currently. Compared with binary LDPC codes, nonbinary LDPC codes not only has the advantages of flexible codes design but also has lower error-floor and better error correction capability. And it’s more suitable for high-order modulation system of high-speed transmission. Based on the study of the construction of parity-check matrix, encoding and decoding method, this paper proposes a soft-decision decoding algorithm of LDPC codes for soft-spread spectrum modulation. And the FPGA design on this decoding algorithm is completed. This decoding algorithm can achieve information transmission at low signal to noise ratio. The main contents and results are as follows:1.Basic theories of the constructing algorithms for parity-check matrix of LDPC codes, encoding and decoding method are introduced.2.The produce method of pseudo-random code, the principle of spread spectrum and despread spectrum are described carefully. Finally, the simulation show that as the modulation order increased, the required bit energy to noise ratio is reduced for achieving the same error rate.3.Firstly, the Belief Propagation(BP) decoding algorithm and the improved Fast Hadamard Transform Belief Propagation(FHT-BP) decoding algorithm of nonbinary LDPC codes are discussed. Secondly, A FHT-BP soft-decision decoding method is proposed which combines the 64-ary soft-spread spectrum modulation technique with LDPC coding at the sender and combines despread spectrum with demodulation at the receiver. Finally, simulation shows that the algorithm can achieve better performance at low signal to noise ratio.4. The FPGA design on soft-decision decoding algorithm of soft-spread spectrum modulation for LDPC codes in baseband system is completed, and which verifies the validity and reliability of the FPGA design.