Research And Applicance Of Turbo Code's Decode Algorithum

Turbo codes has been arrested great attention since it was proposed in 1993 for its excellent near Shannon limit performances, there are lots of researchers were working on it, lots of improvements were founded. it also was applied in many fields. But turbo codes still has some disadvantages. Such as big calculate consumptions, long system time-delays and big memory requirements. This paper will concentrated on the time-delay and memory requirements problems, and the application of Turbo codes in the time-variant multi-path channel.Paper firstly introduced the principle and structure of Turbo codes, then gives the theory, deduce procedure and calculate steps of decoder algorithm. Then,the influence of system parameters on the error correcting ability was discussed. Parameters like the type of interlever , length of restriction, length of interlever block ,number of iteration and rate of the codes were involved .In the third part, paper discussed the Turbo decoder algorithm, proposed two algorithm improvements. The first one is about iterate stop criteria with pre-estimate error bit rate. It based on the time-delay analysis and error bit rate bottom limit of CRC codes which was regulated in 3GPP.Simulation proves the improvement decrease the number of iteration and the interval decoding time-delay while stayed the same error correcting level. The other one is aimed at the modify function of Log-MAP algorithm, this paper present a new fourth power Newton interpolated function to replace the original non-linear function, the improvement saves the table-searching time and reduces memory space without performance decrease.Finally, the main character of wireless mobile environment was introduced, the emphasis is put on time-variant multi-path channel, introduction includes the principle and module of the channel. Then Paper discussed the performance of Turbo codes in the time-variant multi-path channel.The optimization of Turbo decoder algorithm and the study on Turbo code's application under WSSUS channel, not only improves the performance of Turbo code, but expands its application area. In all, the paper provides some useful helpfor the future research and application of Turbo code.