采用辅助网格的4D-8PSK—TCM维特比译码

由于地球探测卫星(EESS)的不断增加,空间数据传输的频带日趋拥挤.为此,空间频率协调组织(SFCG)建议采用高效率调制技术(调制效率不低于1.75 bit/symbol)进行数据传输,以有效地利用空间的频率资源,从而避免由于拥挤导致的临近频带之间的相互干扰. 4D-8PSK-TCM是CCSDS(空间数据系统咨询委员会)针对SFCG关于EESS 8025N8400 MHz频带调制效率不低于1.75 bit/symbol的高效率调制要求而提出的高效率编码调制标准,在满足抗噪声性能要求的基础上,有效地提高了频带利用率.本文研究了调制效率为2.5比特/符号的4D-8PSK-TCM系统及其维特比译码算法,并在Matlab Simulink下进行了维特比译码算法的仿真.在算法实现中,针对路径度量的复杂性,采用了一种辅助网格的方法,使计算路径度量时只需要64次比较,相对于直接计算所需的2032次比较,极大降低了路径度量的运算复杂度.

Auxiliary Trellis Based Viterbi Decoding Algorithm Research of 4D-SPSK-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.