Design And Implementation Of HF Channel Simulator With Multi-channel And Multi-bandwidth

The estimation of the channel is a crucial link that cannot be lost in the process of developing various communication systems.It can be said that in many cases,communication technologies are often developed to solve the adverse effects of channels on the signals.In the research of HF communication systems,it is necessary to test the communication equipment.If testing with the real HF channel,it will cost a lot.Besides,the channel parameters cannot be controlled during the test in the real HF channel,and it is not possible to test the communication equipment multiple times in the same channel environment.However,developers can make tests in the laboratory environment easily with the channel simulator based on the characteristics of the HF channel.Undoubtedly,it has great practical value,and will reduce the cost and cycle of development greatly.Therefore,the development of channel simulators is very important.Firstly,the characteristics of the ionospheric reflection channel and the HF wave propagation characteristics are introduced in this thesis.The multipath effects,fading,Doppler shifts,Doppler spread,and radio interference are discussed emphatically.The causes of these problems and their impacts on HF communications are analyzed.Secondly,according to the characteristics of the channel,the HF channel is described in mathematics,and the relationships among the characteristics of the fading channel in statistics are deduced.The typical parameters of two classical channel models,Watterson model and ITS model,are analyzed and deduced and the specifications of the channel simulator are given in this thesis.Then,according to the specifications given,a channel model framework based on the Watterson model is built which can meet the requirements.Two algorithms to implement fading: sine wave superposition method and shaping filter method,and two kinds of multi-channel noise generation algorithms: filter method and spectrum shift method,and hilbert transform,doppler shift,multipath delay implementation and other signal processing algorithms are simulated and analyzed.Finally,a HF multi-channel multi-bandwidth channel simulator is implemented with the TMS320C6455 hardware platform.It can automatically judge whether there are useful input signals,and it can also add a specified frequency offset,multipath delays,fading rates,and noises to the useful signals.In the single-channel mode,it can select four kinds of working bandwidths,3k Hz,6k Hz,12 k Hz and 24 k Hz.In the multi-channel mode,it can add noises with different SNRs in four channels,300Hz~3300Hz,3300Hz~6300Hz,6300Hz~9300Hz,9300Hz~ 12300 Hz.Performance tests were performed on each function and all of them meet the design requirements.The channel simulator has been applied in the performance tests of a number of HF communication systems and has a good response.