Development Of Physical Simulator Of High Frequency Channel

Shortwave communication plays a vital role in long haul communications, on account of its unique merits such as low cost, convenience to be generated and strong resistance to damage. The physical simulation of shortwave channel enables researchers to simulate particular channel environment in the lab, which is beneficial to the research and test of shortwave communication system. Thus it has marvelous value of application.Simulator presented in this paper provides a direct interface for the test of shortwave communication system, which well represents various features of HF channel such as Multi-path delay, Rayleigh fading, Doppler shift, Doppler spread, Gaussian noise and Impulsive interference, etc. In order to realize the channel simulation for the Intermediate Frequency signal, we, inspired by the idea of Soft-defined Radio, bring forward a new design method that the channel simulator consists of several DSP chips. This paper focuses on the following aspects:1. A new approach is put forward with regard to the IF signal, which applies to physical simulation of baseband and IF channel and has a bandwidth within 12 KHz. This approach realizes channel simulation by combining special DSP chips with universal DSP chip, after the sampling of high-speed IF signal.2. Based on Watterson Model, this paper concentrates on the realization of Doppler shift and Doppler spread based on DSP. Real-time production of Doppler shift with a minimum precision of 0.1 Hz is realized by means of interpolation on the basis of lookup method; simulation of Doppler spread is realized by using the Gaussian shaped FIR filter and linear interpolation technique.3. A prototype of HF channel physical simulator is developed. This paper also analyses some key hardware techniques and the software flow sheet. The prototype is finally tested and the research achieved the design goal.