Turbo Code Decoding Algorithm And Its Dsp Implementation

Turbo codes have been arresting great attentions from the academia of communications and informatics since 1993 because of their excellent performance in error correction. The theory of Turbo codes and the condition of the development are simply introduced in this paper. Under the analysis of decode algorithms, we adopt the algorithm of Lookup-Log-MAP to implement Turbo decode with digital signal processor (DSP).Firstly, the principle of channel codes and turbo codes are introduced in this thesis. Secondly the principle of the decode, the deducing and the step for calculation of Log-MAP algorithms are discussed, and then modify the algorithm, simplify the encoders structure, reduce the complexity of the algorithm and the storage of the memory needed in order to implement the decoder with digital signal processor . Through simulating this modified algorithm we get the satisfied results.Finally, some important problems are considered in order to implement the decoder with fix-point digital signal processor (DSP), such as fix-point quantification, over-flow of calculation and RAM space needed. A way to avoid over-flow of calculation is presented, and it can avoid over-flow of calculation effectively .With the way to deal with some important problems mentioned above, Turbo decoder is implemented with fix-point digital signal processor (DSP). The test result shows the performance of the decoder is close to that of float-point one.