The Performance Evaluation Of PCM/FM Under The Plasma Sheath Environment

When space aerocraft reentries atmosphere at a hypersonic speed, a layer of plasma sheath will come into being on the surface of space aerocraft because of high temperature、high pressure and friction with atmosphere。The existence of plasma sheath will exert severe influence on communication of space aerocraft with ground。The telemetry system of PCM/FM has the highest accuracy among the commonly used telemetry systems, and it has the advantages of flexible telemetry data format、it’s convenient for the receiving and transmitting terminal to process data、it’s adapted to the large-scale integrated circuit technology、it can manage data by connecting with terminals directly。This paper analyzes the principle of how plasma sheath generate and its influence on signal, studies the characteristics of plasma sheath channel and the commonly used theories of communication channel modeling; It builds a plasma sheath channel model, and implements the PCM/FM modulation and demodulation algorithm under the platform of MATLAB; Based on this, it builds the PCM/FM simulation system with the influence of plasma sheath。By watching waveforms of modulation and demodulation we can find that this system implement the PCM/FM modulation; and we know the performance of demodulation by watching the eye diagram; At last, it analyzes the influence of main parameters such as:signal to noise ratio、uniform noise upper limit、 phase noise、Rice factor and transmission coefficient on system。This paper proves that because of the influence of plasma sheath, FM modulated signal will bring jitter which will affect the performance of the system。The simulation results shows that increasing transmission coefficient and signal to noise ratio etc. will greatly improve the performance of the system。It can provide some reference for the communication under the plasma sheath, there are theoretical significance and practical value。...