Mixed Turbo Code Performance Analysis And Applied Research

Channel coding is one of the important part of communication system, whose theoretic base is the Shannon's law of channel code set up by Shannon who inaugurated the information theory in 1948. In the last half century, researchers have always been searching good code with rate closing to the Shannon theory limitation, error ratio being low and it being to be decoded easily. Such code is also called gradually good code or Shannon code.In 1993, C. Berro etc. firstly proposed a new channel code method-Turbo code, which employed Recursive Systematic Code, the random interleaver,MAP(Maximum A Posteriori) algorithm and iterative decoding algorithm obtained the capacity that had only 0.7dB difference compared to the Shannon limitation. Turbo codes immediately got the extensive notice for their miraculous performance, then became the research hotpot of theinternational information theory and code theory.Turbo codes represent the new code structures, which consist of PCCC(Parallel Serially Convolutional Code) and SCCC( Serially Concatenated Convolutional Code). In this paper , the background of turbo codes are firstly introduced, which includes the base principle of Error Correction Code, Block code and Convolutional code; the principle of turbocode and the iterative decoding is secondly expanded; the key decoding algorithm: a revised MAP algorithm and iterative decoding theory are detailed; then, a new turbo code structure : HCCC(Hybrid Concatenated Convolutional Code) is presented, and the capacity of this code method is analyzed ,the average capacity upper bound is derived; at last ,this code is simulated on AWGN(Additive White Gaussian Noise) channel and Rayleigh fading channel. The simulation result shows that: the performance of the proposed scheme is improved with comparison to PCCC and SCCC on both AWGN channel and the Rayleigh fading channel. In AWGN channel, it is about same if the SNR is low, if the SNR is high, the improvement is 0.2~0.5dB. In Rayleigh channel, the capacity is also improved.