Code-aided Synchronization Algorithm For LDPC-OQPSK System Of Deep Space Communication

Deep space communication is an important guarantee for space exploration and spacedevelopment. Deep space communication has the characteristics of long distance, limitedsignal power, severe attenuation and poor channel environment, with the technologyevolution, promoting the transmission system is the most direct and effective way to improvethe transmission performance and the reliability of the deep space communication. In themodified technology system, channel coding, modem and synchronization technology occupya key position and also need to be developmented.The most outstanding performance of LDPC codes are researched and discussed deeplyin the thesis, combined with the offset quadrature phase shift keying modulation which hashigh bandwith utilization and power utilization and is smaller affected by the nonlineary, theiterative decoding bit interleaved coded modulation system model is set up, and the iterativereceiver mechanism is designed. In low SNRs, conventional synchronization methods can notachieve accurate carrier synchronization, so based on the code-aided carrier synchronizationideas, the soft decoding information is used to assist estimating the synchronizationparameters. By conducting the joint iteration of synchronizer, demodulator and decoder thedeep space communications receiver model is construced.First, closely tracking the development of the deep space communication, a summary ismade on the research achievements of domestic and foreign scholars in the coding andsynchronization technology of deep-space communication systems and the existing problemswere summed up.Second, the advantages and disadvantages of the traditional synchronization methods areanalysed, an overview of the principle of maximum likelihood estimation is made, and twocode-aided carrier synchronization algorithms based on maximum likelihood estimation arestudied theoretically.Third, on the basis of analyzing the characteristics of deep space communications, theLDPC codes and OQPSK modulation are used to establish the BICM system with iterativedecoding. The simulation results are given involving various parameters including differentthe code lengths, code rates, construction methods, iterative times and etc. After that the appropriate parameters are determined.Finally, using the BICM system with iterative decoding, the effect of carriersynchronization on the system performance is analyzed, and the code-aided synchronizationalgorithm is used in order to obtain accurate carrier synchronization in low SNRs, and themean square error and bit error rate of carrier synchronization in different system parametersare simulated and analyzed to verify the effectiveness of the proposed method. The theoreticalanalysis and simulation results both show that: the deep space communication iterativereceiver model in this paper can ensure the reliability of deep space communication.