Real-time Prediction Method For Plasma Sheath Channel Characteristic

The hypersonic aircraft will produce a "plasma sheath" on its surface during reentry.The plasma sheath will produce different degrees of reflection attenuation and absorption attenuation of the electromagnetic wave,which will deteriorate the communication quality.In severe cases,the communication may be interrupted and a "black barrier" phenomenon may occur.In order to realize the reliable information transmission under the condition of “black obstacle”,the premise is to understand the channel characteristics of the plasma sheath,and adapt the communication technology and system to the plasma sheath channel,thus establishing a communication method suitable for the plasma sheath.Therefore,this paper proposes a real-time prediction method for measuring the plasma sheath channel based on the reflected signal.By extracting the influence of the sheath parasitic modulation effect in the reflected signal and combining the correlation between the reflected signal and the transmitted signal in the plasma,the performance is reversed.The effect of the sheath on the transmitted signal,and then the characteristics of the sheath channel are calculated.At the same time,the real-time estimation method is designed and implemented for the real-time estimation method,including the design of the reflected signal extraction scheme,the design of the data processing scheme and the hardware.The construction of the platform,and finally the experimental verification of the real-time prediction system,verified the feasibility of the prediction system under experimental conditions.The main research contents and contributions of this paper are as follows:(1)Based on the theoretical analysis of the characteristics of radio wave propagation and plasma channel characteristics,a real-time calculation method for estimating the characteristics of the plasma sheath from the signal transmitting end is proposed.Firstly,the correlation between the reflected signal and the transmitted signal in the plasma sheath is performed.Analysis provides the basis for the estimation method;the core part of the steadystate,dynamic plasma channel real-time prediction method can be divided into three parts,one is to use the reflected signal power to estimate the average electron density of the plasma sheath channel,and the second is The transmitted signal is estimated by the reflected signal.The third is to use the estimated transmitted signal to analyze the characteristics of the plasma sheath.For the steady-state plasma,the attenuation characteristic prediction method is based on the amplitude negative correlation,and the amplitude of the reflected and transmitted signals is corresponding.The relationship is formulated.From the perspective of theory and simulation verification,the projected signal power corresponding to the interaction between the reflected signal power at different radio frequency frequencies and the formula is obtained,and the channel attenuation characteristics are obtained.Based on the phase positive correlation,the delay characteristic estimation method obtains the fixed phase difference between the reflection and transmission signals for the collision frequency segment,and predicts the phase of the transmission signal in real time by using the phase of the reflected signal,and obtains the channel by estimating the phase of the estimated transmission signal.Delay characteristics.The dynamic channel uses the sinusoidal jitter plasma sheath as the research model.The steady-state estimation algorithm is used to extract the influence of the sheath parasitic modulation on the signal.The power and amplitude correlation characteristics of the time-varying reflected signal are used to construct the timevarying transmission signal power expression.The probability density distribution acquires the attenuation characteristics under time-varying channels.Due to the synchronous modulation of the phase of the signal by the dynamic plasma sheath,the phase of the reflected and transmitted signals is only related to the fixed phase difference.The probability density of the reflected signal phase directly reflects the time-varying channel.Delay characteristics.(2)Based on the above-mentioned proposed real-time estimation method of sheath channel characteristics,the design and implementation of real-time estimation system is carried out.The real-time prediction system design includes the reflection signal extraction scheme in the microwave front-end circuit,and the joint simulation scheme of ADS and CST The feasibility of the verification is carried out.In addition,the data processing scheme is written by Quartus II software and verified by Modelsim.The real-time estimation system implementation includes hardware platform construction and related testing.The hardware platform is divided into front-end circuit part and back-end data.In the processing part,the hardware implementation of the front-end circuit part is consistent with the design principle of the microwave front-end circuit module,and the module is initially tested after the completion of the construction.The back-end data processing part is mainly composed of an AD acquisition card,an FPGA development board and a computer.The data processing core algorithm mainly performs real-time processing on the external signal of the microwave front-end circuit output,and the system is tested as a whole after the completion of the construction.(3)The experimental verification of the real-time prediction system mainly combines the front-end circuit part and the data processing part to carry out the measurement experiment of the real-time prediction system under the steady-state and dynamic plasma sheath environment,and relies on the real-time prediction method to the experimental environment.The sheath characteristics of the sheath are estimated in real time,and the feasibility of the estimation system and the estimation method under experimental conditions is determined.