Techniques On Synchronization And Blind Equalization In HF Interception System

HF communication is widely used in military communications due to its strong anti damage performance and the convenience in its reconstruction.In recent years,non-cooperative HF communication has attracted more and more attention due to the development of communication reconnaissance and information countermeasure.Based on the needs of non-cooperative HF communication and the software design project of"MPSK blind demodulation module",the technologies of synchronization and blind equalization in HF interception system are studied in this thesis.Firstly,a detection method based on signal constellation dispersion measurement is proposed to overcome the difficulty in determining whether the signal exists due to a lack of prior information such as training sequence and frame structure.Simulation results show that the method is suitable for low SNR of HF channel.Besides,based on the requirements of the project,a method of locating the starting and ending positions of burst-signal in HF interception system is also investigated in this thesis,so as to provide reference for subsequent processing modules.Secondly,methods about error estimation synchronization algorithm based on cyclic-autocorrelation-function and adaptive loop synchronization algorithm based on PLL are studied in this thesis to resolve the problem that the performance of demodulation is seriously affected because of symbol rate deviation and carrier frequency deviation in the receiving signal of HF interception system.An improved symbol synchronization algorithm of initializing PLL parameters with error estimate results is proposed for synchronization with large symbol rate deviation,with simulation results showing that the steady-state error after synchronization is less than 0.17%.A carrier synchronization method of error estimation aided loop synchronization is studied for the burst-signal,with simulation results showing that the residual frequency deviation after synchronization is less than 0.2Hz.Thirdly,according to the project requirements and signal characteristics,two blind equalization algorithms of improved CMA and data reuse CMA for burst-signal are investigated in this thesis to eliminate the serious inter-symbol interference in HF communication.The simulation results show that the improved CMA blind equalization algorithm has faster convergence speed and smaller steady-state error,and the improved algorithm can also correct the residual carrier frequency deviation not greater than 0.3Hz.Finally,based on the algorithms of each module,the HF interception blind demodulation system is simulated with QPSK modulation,1 Baud symbol rate deviation and 10%carrier deviation.The simulation results show that its performance degradation is less than 3dB compared with that with no frequency and symbol rate deviation under AWGN channel;and its error rate is lower than10^-4 under multipath channel with 22dB SNR.The simulation results prove the effectiveness of each module algorithm and blind demodulation system.Then,the"MPSK blind demodulation module"software system is designed,and its performance is tested,the results show that the demodulation software system well meets the requirements of the project.