Research On Demodulation Technologies Of 8PSK Modulated PCMA Signals

Paired Carrier Multiple Access(PCMA)is an advanced satellite communication technology in which two communication parties use the same frequency band,which greatly improves the frequency utilization ratio of the satellite channel and has high anti-intercept performance.Therefore,PCMA technology has been widely used in satellite communications.The key issue to PCMA communication systems is how to recover the useful signal sequence from the mixed signal.For cooperative received 8PSK modulated PCMA signal,this paper focuses on the parameter estimation of self-interference signal,the separation and demodulation algorithm based on interference cancellation and the joint separation and demodulation algorithm based on PSP.The main works are as the following:1.For the parameter estimation of the self-interference signal,the modified Cramer-Rao Bound(MCRB)of frequency offset and time delay joint estimation are derived.A frequency offset estimation algorithm with timing synchronization is proposed.Simulation results show that the algorithm has similar performance with M&M algorithm,but its complexity is reduced by 2 3.A joint estimation of frequency offset and time delay is proposed by combining the delay detection method of correlation detection.The sequence samples stored locally are used as auxiliary data.Estimation of frequency offset and time delay is calculated by optimizing the objective function,which is obtained from the cross-correlation computation of the auxiliary data and mixed signal,and the optimized process is accomplished by utilizing two-dimensional search.By setting the threshold of joint estimation,the calculated amount is greatly reduced.Simulation results show that the frequency offset estimation performance is equivalent to that of the joint estimation algorithm.2.Based on the idea of mixed signal separation before demodulation,adaptive interference cancellation filter is used to separate the signals.The hard-decision demodulation algorithm based on constellation and the Maximum Likelihood Sequence Estimation(MLSE)based on Viterbi are studied respectively.Simulation results show that the traditional hard-decision demodulation method based on constellation diagram is sensitive to the separation error of mixed signals,and the MLSE algorithm based on Viterbi can get better demodulation performance;The algorithm performance of MLSE could be improved by oversampling.3.For 8PSK and other high-order modulated PCMA signals,demodulation algorithm based on Decision Feedback Per-Survivor Processing(DF-PSP)is proposed.The algorithm consisted of twice sequence estimation: first,the traditional hard-decision demodulation method based on constellation diagram is employed to obtain the preliminary decisions of useful signal;The second uses PSP algorithm with truncated channel.At the same time,The hard-decision results are used as feedback,in order to compensate the performance loss caused by truncated channel.Simulation results show that the DF-PSP algorithm can provide the tradeoff between complexity and performance,which can improve demodulation performance effectively while reducing the complexity.