Improvement And Application Of Soft Output Viterbi Algorithm

Turbo codes have been widely used in various fields including modern mobile communication,broadband wireless communication and deep-space communication.And the iterative decoding method of turbo codes also provides solutions for many communication problems,including channel estimation,equalization and multi-user detection in mobile communication system.As a fast decoding algorithm of turbo codes,the soft-output Viterbi algorithm(SOVA)is widely used due to its low computational complexity and low storage space.Firstly,in this thesis the Viterbi algorithm and Lazy Viterbi algorithm are introduced,and eight kinds of soft-output Viterbi algorithms are studied deeply,including HR-SOVA,BR-SOVA,LR-SOVA,Bi-SOVA,S-SOVA,R4-SOVA,Ad-SOVA and T-SOVA.Moreover,the performance of eight algorithms are simulated,and their computational complexity are analyzed,the decoding delay of T-SOVA with different reduction factors are counted.Secondly,the improved methods of SOVA are proposed:(1)a modified R4-SOVA for the code with short and odd length is proposed,and the bidirectional decoding method is combined to improve the performance of R4-SOVA;(2)through the research of trellis diagram and traceback process,an improved SOVA with variable sliding window(ASW-SOVA)is proposed that reduces the average traceback length;(3)to further reduce the decoding delay,a simplified adaptive idea is combined with T-SOVA whose reduction factor is small;(4)the proposed idea of variable sliding window is combined with T-SOVA(ASW-T-SOVA)to further reduce the average traceback length;(5)in order to use T-SOVA in SCCC's outer decoder,a new T-SOVA based on Viterbi algorithm called VB-T-SOVA is proposed,then its performance and decoding delay are compared with T-SOVA in turbo codes.In this thesis,the improved algorithms are simulated respectively,and their computational complexity and decoding delay are analyzed and counted.The results show that the new algorithms in this thesis are practical.Finally,the Inter-Symbol Interference(ISI)channel model and turbo equalization are introduced.Then,the proposed VB-T-SOVA and ASW-SOVA are applied in the equalizer as equalization algorithms.The performance simulation shows that the improved methods can also use in turbo equalization,and the decoding delay is reduced with bit error rate unchanged.