Optimal Decision Method Of Angle Modulation Signal Under Dynamic Plasma Sheath

When the space vehicle is flying in the adjacent space at ultra-high sound speed,the surface of the air vehicle will generate violent friction with the air.Under the action of high temperature and pressure,the air will be ionized,and a layer of "plasma sheath" will be formed on the surface,which will seriously affect the transmission of communication signals and even lead to communication interruption.Relevant studies show that when the communication signal is transmitted through the plasma sheath,most of the energy of the signal cannot penetrate the plasma.Even if the ground monitoring station can receive the signal,the dynamic characteristics of the plasma will still lead to deterioration of the communication quality.Therefore,it is necessary to study the influence mechanism of isodynamic ionic bodies on communication signals from the perspective of signal processing.The theory and experiment show that the plasma is unstable and time-varying,and the dynamic characteristic not only causes the serious power attenuation of the communication signal,but also causes the phase jitter,which is called the parasitic modulation effect.In this paper,the effects of parasitic modulation effect on angular modulation signal transmission caused by plasma dynamics are studied in the following aspects:1.Introduced the basic characteristic parameters of plasma and the dynamic plasma channel modeling method used in this paper,and further studied the radio wave propagation characteristics and channel characteristics under the dynamic plasma.The reason of parasitic modulation effect and its influence mechanism on communication signal are analyzed,and the relationship between the attenuation coefficient of communication signal after passing through the dynamic plasma and the plasma parameters is verified.2.The influence of dynamic plasma on Angle modulation signal is studied.Angle modulation includes frequency modulation and phase modulation.Through theory and simulation,it is found that plasma dynamics seriously affects channel capacity of anglemodulated signal,among which plasma thickness and dither variance have the greatest influence on channel capacity.3.Through the estimation of channel capacity of Angle modulated signals under dynamic plasma,we find that the use of traditional judgment method leads to greatly reduced channel capacity of QPSK signals.To solve this problem,this paper demodulates QPSK signals passing through dynamic plasma by spectral clustering method,which to some extent alleviates the problem of high bit error rate caused by dynamic plasma to QPSK signal transmission.Finally,a fuzzy spectral clustering method is proposed to detect QPSK signals in the optimal decision,so as to further reduce the bit error rate during transmission.4.Carry out experimental verification of fuzzy spectrum clustering judgment method through the software radio platform,use the plasma generation device developed in the laboratory,and build a QPSK modulation signal transceiver system combined with the software radio platform.The fuzzy spectrum clustering decision method is introduced into the software radio platform to carry out the real-time communication experiment of QPSK signal under the plasma environment,and the influence of the plasma dynamics on QPSK signal transmission is reduced.