Studies On Some Key Problems Of Turbo Codes

Turbo code is a new class of error-correcting codes that can approach the Shannon bound. It is considered as the most exciting and potentially important development in coding theory in recent years. Its invention has changed the conventional design principles of the coding scheme from the attempt to increase the minimum Hamming distance of the code to the goal of reducing the number of code words with low Hamming weights.This thesis investigates some problems of turbo codes with emphasis on the turbo theory, the quantization of the turbo decoder and its performance, and so on. The main results and contents of this dissertation covers the follows:1. The development of the theory and technique of channel coding is outlined; the development and application of turbo codes is also discussed.2. The principle of iterative decoding of turbo codes is illustrated, and the decoding algorithm for turbo codes over AWGN channels is described.3. The concept of self-terminated sequence is introduced with some of its useful characteristics being proved and its relation with lowest weights of RSC being discovered. Moreover, a very tight upper bound of the weight of the RSC is given.4. The characteristics of the self-terminated sequences interleaved are examined. In particular, when considering the affections on the weight distribution of Turbo codes caused by the weight 2 self-terminated sequences, the distribution of low weights of Turbo code can be calculated conveniently.5. For different decoding algorithm and different signaling schemes, different quantization schemes are used. The nonuniform quantization method for the special property signal is put forward for the first time. Accomplish the turbo component encoder in fix parameters using recursive convolutional code, interleaver, puncturing model, and MAP (maximum a posteriori) decoder.As the selected code of 3GPP, the study of turbo code is of great significance. The application of turbo code still faces some problems. The study of quantization and decoding on AWGN channel is intended to solve the application problems. There are many problems left on the turbo theory which need advanced studies.