Research On The Critical Technologies Of HF Digital Communication System

HF communication which has the advantage of good mobility, strong stubborn existence and etc, plays an important role in military communications. Because of its time variantity and vulnerability to the effects of ionospheric disturbances, HF communication is poor at stability and reliability. In order to improve the quality and link performance of received signal, based on the "study of XXX HF communications transmission technology" project, our study focus on two key technologies: adaptive equalization and channel coding.In the first place, based on the characteristics of HF channel, the impact of its multipath effect and doppler effect on data transmission was analysed and simulated, HF channel simulation model based on Watterson model was constructed and realizable algorithm for this model was provided.Then, based on the fundamental principles of adaptive equalization, we analysed convergence and traceability of LMS and RLS which was proved to be better in convergence and traceability; the impact of tap number of linear equalizer and Decision Feedback Equalizer(DFE) on equalization of HF channel was simulated, it was shown that DFE was more suitable for HF channel characteristics and its experimental protocol had certain reference value.Finally, based on the coding techniques of fading channel, RS code,convolutional code and Turbo code were chosen, Monte Carlo Method was used to discuss the performance of HF digital communication system. improved by concatenated code,convolutional code and Turbo code which were modulated by QPSK. It was shown that, under the same modulation, to achieve the same bit error rate, concatenated code could obtain more coding gain than single code and the system did not increase in complexity; under the same complexity,Turbo codes obtain more coding gain of around 2dB than convolutional code。These results have been directly applied to designning the launch programme and achieved good performance.