Synchronization And Iterative Equalization Technology In HF Communication

High frequency(HF)communication has a long transmission distance,convenient equipment and is not restricted by relay,which has always been an important part of global information dissemination.Because the HF long-distance transmission depends on the reflection in the ionosphere,and the ionospheric environment is unstable,which makes the short-wave channel have multipath effect,fading,Doppler frequency shift,frequency spread and so on.The study of key technologies in HF communication,such as signal detection,frequency offset estimation and Iterative Equalization,can improve the reliability of communication system.This paper mainly studies the signal detection,frequency offset estimation and Turbo Equalization in HF communication.The contribution in this paper can be summarized as follows:1.The characteristics of HF channel transmission and waveform parameters in Appendix D of MILSTD-188-110C protocol are introduced.The Watterson channel model of HF narrowband classical channel is studied,and the Watterson channel model is simulated and analyzed according to the typical channel parameters of HF.The analysis results show that the Watterson channel model can well reflect the narrowband HF channel characteristics.2.The double correlation signal detection algorithm and the grouped double correlation signal detection algorithm are studied,and the grouped double correlation signal detection algorithm is simplified.By simulating the detection performance of the three algorithms with different SNR and Doppler frequency shift,the analysis results show that the simplified grouped dual correlation signal detection algorithm has slightly lower detection performance and anti-frequency offset performance than the two algorithms.By simulating the detection performance of the three algorithms in different HF channel environments,the analysis results show that the simplified group-based bispectral signal detection algorithm is still suitable for HF channel.3.The double correlation based frequency offset estimation algorithm is deduced.The simulation results show that the double correlation ased frequency offset estimation algorithm is a low complexity,wide estimation range and high estimation accuracy.The simulation analysis of the influence of the number of segments on the estimation range and accuracy of the algorithm shows that the algorithm based on the dual correlation can further improve the estimation accuracy at the expense of the estimation range.4.The influence of forgetting factor on Turbo Equalization performance and the relationship between recoding and iteration times are studied.Through the simulation analysis of different forgetting factors on Turbo equalization bit error rate,it is shown that the forgetting factor has the optimal value to make the Turbo equalization bit error rate lowest under the given channel environment and iteration times.Through the simulation analysis of the bit error rate of recoding,it shows that in practical engineering,recoding can be used to realize the function of automatic stop iteration.