Auxiliary Trellis Based Viterbi Decoding Algorithm Research of 4D-8PSK-TCM

Four-Dimensional 8PSK Trellis-Coded Modulation(4D-8PSK-TCM)is recommended as an efficient coded modulation standard for the Earth Exploration Satellite Service(EESS)8025-8400 MHz band by the Consultative Committee for Space Data System(CCSDS).The advantage of 4D- 8PSK-TCM is that coding gains can be achieved without expanding the bandwidth relative to the un-coded signal set.In this paper,the 4D-8PSK-TCM system with the modulation efficiency of 2.5 bit/symbol and its Viterbi decoding are presented and the Viterbi decoding algorithm is implemented on Matlab Simulink.During the algorithm implementation,an auxiliary trellis is introduced to reduce greatly the number of computations of metrics of each path.In this way,there are only 64 comparisons to compute the metrics in comparing with the 2032 comparisons required in a directly computing approach.