Research On Improving The Performance Of Turbo Codes

As a kind of channel encoding scheme in 3G mobile communication system, Turbo codes influences the property of system, so increasing the performance of Turbo codes can improve the communication quality of system. This paper discussed the theory of encoding and decoding of Turbo codes, researched some key techniques in encoder and decoder, analyzed the question of selection of the component codes and generation polynomial in encoder. At the same time, the simulation analysis on the decoding performance of Turbo codes was given, and the results show that under the certain conditions, Turbo codes approaches the theoretical Shannon limit, which proves its excellent performance of decoding. Besides, according to a great deal of simulation results, the influence of selection of designing parameters on Turbo codes was analyzed, at last the principle and method of selecting parameter were concluded.The optimum decoding algorithm-MAP algorithm and its improved algorithm in logarithm domain used in Turbo codes were derived, combining them with the stop criteria of iteration hi realization of decoding, an improved algorithm using fading factor was introduced. Simulation results show that the algorithm can improve the performance of Turbo codes decoding.The primary theory of interleaver, its function in Turbo codes and the influence of its struction on the performance of Turbo codes were presented. Then several typical interleaves used frequently in Turbo codes were mentioned, according to the analysis of them, the designing criteria of interleaver in Turbo codes was summrized. Based on that, combining the criteria with the theory of block interleaver and semi-random interleaver, a design scheme of combined interleaver was introduced. Simulation results show that the interleaver compromises the advantages and the disadvantages of block interleaver and semi-random interleaver, which decreases the bit error rate of Turbo codes of long data frame.Turbo codes was usually realized by using DSP or FPGA, the two schemes have their own advantages and disadvantages. Aiming directly at decoding algorithm of Turbo codes, the paper presented two schemes corresponding the two methods. By comparison, this paper adopted the scheme of using FPGA, and based on that, the realization scheme of interleaver was presented. According to analysis, the two shcemes are practicable and they can be applicated in communication system.