Research And Applications On Turbo Codes For Correcting Synchronization Errors

Insertions and deletions in bit or symbol level are commonly referred as synchronization errors in the procedure of message transmission and storage. Turbo codes based on the extended trellis diagram can effectively correct synchronization errors. In practice, a flipped chip may cause synchronization errors in Different Pulse-Position Modulation(DPPM). In order to solve the problem above, this thesis studies the synchronization error correction scheme with Turbo codes in DPPM system, and investigates the potential of correcting synchronization errors with systematic Turbo codes. Specifically, this thesis includes the following.On one hand, the thesis employs a DPPM transmission scheme which adapts to the nonsystematic Turbo codes for synchronization errors. Due to the variable-length symbols in DPPM, the corrupted single chip by additive noise will lead to synchronization errors. The designed DPPM system with nonsystematic Turbo codes can effectively correct synchronization errors caused during DPPM detection. Meanwhile, according to the characteristic of synchronization errors in DPPM system, the decoding scheme with Turbo codes is optimized to improve the overall performance of DPPM system. It has been demonstrated using simulations that the proposed DPPM system with nonsystematic Turbo codes can achieve significant performance.On the other hand, in order to deal with the scare synchronization errors with in Additive White Gaussian Noise(AWGN) channel, a systematic Turbo scheme which is able to correct insertions, deletions and substitutions is studied. The encoder has the same structure as a conventional one. The decoder has a hierarchical structure. The function of the pre-decoder is to handle insertions and deletions; the purpose of the unit for backtracking is to recovery the sequence from synchronization errors; while the character of conventional Turbo decoder is to correct substitutions. This thesis simulates the performance of proposed scheme over the cascaded channel of Binary Insertion Deletion Substitution channel and AWGN channel, and then analyzes the impact of several parameters on Frame Error Rate(FER).