Research On The Combination Of TTCM And CPM In Deep Space Communication

Channel coding and modulation are two important parts of deep-space communication technologies, which can improve the coding gain and bandwidth utilization through the joint use of high-performance error-correcting coding techniques and bandwidth efficient modulation techniques.Firstly, this paper emphasizes on the performance comparison of some kinds of decoding algorithm of Turbo-codes, including MAP, Log-MAP and Max-Log-MAP. On this basis, a new algorithm called linear Log-MAP is proposed, and the performance of which can be closer to that of the optimal Log-MAP algorithm. Afterward the simulations are shown in terms of the performance of various algorithms, the length of interleaving and the number of iterations. Secondly, a decomposition model of CPM system is elaborated, which shows that a CPM system can be decomposed into a continuous-phase encoder (CPE) and a memoryless modulator (MM). And then the performances of CPM moduation are analyzed from the aspect of CPM signals's spectral bandwidth. After that the soft-output detection algorithm and the structure of continuous phase demodulator are intruduced in detail, and the parameters'impact on the BER of CPM is analyzed. Finally, on the basis of research on existing TTCM, TTCM-CPM serial concatenated coded modulation program is discussed, which integrates the advantages of partitioning and SCCC. Simulation results show that greater performance gain can be achieved through a few iterations.