The Application Of Soft-Decoding In Channel Codeing

Soft Decision Decoding(SDD) makes full use of the information in the received signal wave form, it lets decoder has a more accurate probability to decide the codes received, so it has a important application in channel coding. Compared with Hard Decision Decoding(HDD), using the same algorithm, SDD can gain additional 2~3dB encoding benefit. This thesis researches and discusses about the principle and method of the SDD, then implements and applies SDD, and gives results and data of experiments.First, the principle and method of Soft Decision Decoding is introduced, aiming at some important algorithms—Generalized Minimum Distance (GMD) algorithm and Chase algorithm, this paper has detailed discussion.The Soft Decision Decoding of block codes is an important topic discussed in this paper. Because the SSD of block codes is based on Hard Decision Decoding ,we take BCH codes(RS codes) as an important point to introduce the normal block codes decoding algorithms ,including Error-Trapping Decoding algorithm and its modified algorithm, BM iterative algorithm. Decoding of the Golay code and (15,9)RS code are implemented, simulation experiments show that the decoders of BCH codes and Golay code designed by VHDL can execute the decoding as fast as encoding. Compared with other methods, the decoders reduce the delay time greatly. Based on them, this thesis uses the CHS2 of Chase algorithm to get the SDD of BCH codes, then modifies it to get a better performance and low complexity SDD method, tests it through experiments at last.Viterbi algorithm of convolutional codes and its Soft Decision Decode are important parts in this paper. Based on the implementing Viterbi algorithm of convolutional codes and Soft Decision Decoding, this thesis discusses concatenated code and product code. They are important methods to create long codes and then gain the approximate good codes, also the important research contents in channel coding field. Applying the Viterbi algorithm of convolutional code to the concatenate code, we get a more perfect performance. Then, SOVA, Soft-Output Viterbi Algorithm, an important soft-output algorithm extended from Viterbi algorithm, is discussed; it's realized in this paper. The application of SOVA in iterative decoding of Turbo codes is also discussed. Through showing the process by experiments, we can see the excellent performance of SOVA.