Ldpc Codes And Implementation Of Cofdm Communication System

Recently, as an error-correcting code technology with performance closed to Shannon limit, low density parity check code has gradually became a hot research in channel coding theory and widely applied in wireless communications, deep space communications, optical and magnetic recording fields. With the research of the next-generation wireless communication systems, low-density parity-check code technology with the superior performance of error correction and orthogonal frequency division multiplex technology that possesses high bandwidth efficiency and strong ability of anti-interference, have raised the communication quality and the data rate, which have received great attention. So, in this dissertation, encoding and decoding algorithms of LDPC code are studied, an improved LDPC-OFDM model is analyzed and then a quasi-cyclic LDPC codes decoder is also implemented.Based on these ideas, the main work is summarized as follow in this dissertation:(1) The research of encoding and decoding algorithms of LDPC code. First, the basic principle of linear block codes is introduced briefly. Second, the definition of LDPC code and several important structure and encoding algorithms are studied. Finally, the basic principle of decoding algorithms are analyzed, especially BP algorithm, log-BP algorithm and BP-Based algorithm, Normalized BP-Based algorithm and offset BP-Based algorithm that based on check information revised approach. And then the correcting performance and decoding complexity are balanced for picking out the most suitable algorithm for implementation.(2) The application and performance analysis of LDPC code in OFDM communication system. First of all, the characteristics of OFDM system are analyzed. Secondly, several improved technologies are studied in depth, such as adaptive modulation technology, adaptive bit allocation technology, adaptive power allocation technology and channel estimation technology. Finally, aiming to the defects of universal LDPC-OFDM model, an improved LDPC-OFDM model is proposed, and then its performance impaction is also analyzed by simulation. The simulation results show that LDPC-OFDM model has good performance, and apply a reference to the future broadband wireless communication systems using LDPC-OFDM model. (3) The FPGA implementation of quasi-cyclic LDPC decoder. Aiming to the shortcomings of the tradition decoder architecture, the improved partially-paralle decoder architecture is proposed, implemented and verified on the device Altera Cyclone II EP2C70F896C6. And for a given quasi-cyclic LDPC code, two effective ways (pipeline processing and scheduling algorithm) to improve the decoder throughput are proposed in this dissertation. The experimental results show that the decoder possesses simple logic control, low time delay and high resource using. By performing maximum 10 decoding iteration at 190.99MHz, the improved decoder that based on scheduling algorithm, could achieve a maximum bit throughout of 104.18Mbps to basically meet the requirement of the future broadband wireless communication systems.