The Research Of Turbo Decoding Algorithms

Turbo codes were first introduced in 1993 by C.Berrou et al, they are parallel concatenation of recursive systematic convolutional codes whose encoder consist of a parallel concatenation of two or more convolutional codes, and its decoder uses a soft-input/soft-output feedback decoding rule. This kind of codes has given rise to a large interest in the coding theory because of they can still achieve small bit error rate at low SNR close to the Shannon capacity limits. In the development of the third generation mobile communication systems, it is well known that Turbo codes are the way of correct coding of high-speeding data channel. The research of Turbo codes includes the design of the encoder, the interleaver and soft-out/soft-in iterative decoding algorithm.The goal of this paper is to study the Turbo decoding algorithm. Firstly, the backgrounds of this problem and development trendency of Turbo codes are introduced, as well as some problems in this area are pointed out. Secondly, a few of fundamental theory and the structure of Turbo encoder and decoder are described. According to this, some analyses for the performance of Turbo codes are presented. Thirdly, in order to increase decoding rate without any effect on bit error rate, a matrix of decoding for Turbo codes is presented. Then. a linear calibration is put forward which can simplify calculation and make hardware convenient without negative effect on the performance of algorithm process. Lastly, we propose a new "early detection" iterative decoding stop criterion to reduce the considerable complexity of decoding process of Turbo codes. It can accelerate decoding, improve decoding performance through the threshold decision of extrinsic information. So it is possible for Turbo codes to be applied in practice.So far, the study for Turbo codes is not deep enough, especially there are many problems need to be solved in practical area. However, the outstanding features of Turbo codes cannot be denied. It has wide prospect and potentialitywhich will be developed.