Research On3D Turbo Codes And Related Decoding Algorithms

Turbo codes can obtain error correction performance which is near to theShannon limit at low to mediate signal-to-noise ratios (SNRs). However, they exhibiterror floor at high SNRs due to the low minimum distance. To lower the error floorsof Turbo codes,3D Turbo codes could solve this problem by adding a simple rate-1third dimension to traditional Turbo codes. Nevertheless,3D Turbo codes could causeperformance degradation at the low SNRs. Therefore, devising proper coding schemeto optimize the overall performance of Turbo codes is a challenging problem.Simultaneously, in practical applications, demodulators of some communicationsystems could only provide hard-decision results which are not compatible with thesoft-in soft-out decoder of Turbo codes. For the special application scenario, theresearch on the improvement of decoding algorithm is of certain practical significance.Consider the two problems, the main contributions of this thesis are as follows.On the one hand, in order to reduce the performance loss of3D Turbo codes atthe low SNRs, a kind of modified3D Turbo codes was proposed by modifying thestructure of rate-1encoder, which is based on the analysis of the encoding anddecoding algorithms of3D Turbo codes and their performance verification.Simulation results show that, the improved3D Turbo codes could reduce theperformance loss at the low SNRs with nearly the identical error floor. Moreover, theproposed method only brings little additional complexity.On the other hand, for the sake of solving the performance loss of Turbo codes’SISO decoding method result from hard demodulation, an improved method whichmodifies the hard-decision results is to improve the performance loss in the situation.By compensating the initial decoding information with different reliable levels, theproposed method improves the accuracy of hard-decision receiving values fromchannel observation. Simulation results show that, the proposed method could reducethe performance degradation due to the hard-decision results of demodulators.