高超声速飞行器再入过程中会在其表面产生“等离子体鞘套”。等离子体鞘套会对电磁波产生不同程度的反射衰减和吸收衰减，使通信质量恶化，严重时甚至会导致通信中断，产生“黑障”现象。为实现“黑障”条件下的可靠信息传输，前提是要了解等离子鞘套的信道特性，使通信技术与系统适应于等离子鞘套信道，从而建立一种适用于等离子鞘套下的通信方法。因此本文提出了一种基于反射信号测量的等离子鞘套信道实时预估方法，通过提取鞘套中寄生调制效应对反射信号的影响，并结合等离子体中反射信号与透射信号之间的相关性，反演出鞘套对透射信号的作用，进而预估得到鞘套信道特征；另外针对该实时预估方法，设计出一套实时预估装置，包含了反射信号提取方案的设计，数据处理方案的设计以及整体硬件平台的搭建；最后通过搭建的预估装置对该信道预估方法进行实验验证，确定该预估方法的计算精度以及实验可行性。本文主要研究内容和贡献如下：

(1) 基于对电波传播特性以及等离子信道特性的理论分析，首次提出一种从信号发射端对等离子鞘套信道特征进行预估的实时计算方法，首先通过对等离子鞘套中反射信号与透射信号相关性分析，为预估算法提供基础。核心部分的稳态、动态等离子体信道实时预估方法可分为三部分，一是利用反射信号功率对等离子鞘套信道平均电子密度进行粗预估，二是通过反射信号预估透射信号，三是利用预估透射信号对等离子鞘套信道特征分析。对于稳态等离子体，衰减特性预估方法以幅度负相关性为基础，将反射、透射信号幅度的对应关系公式化，从理论及仿真验证的角度，对不同电波频率处反射信号功率与该公式相互作用预估对应的投射信号功率，获得信道衰减特性。时延特性预估方法以相位正相关性为基础，对碰撞频率分段获取反射、透射信号固定相差，并利用反射信号相位实时预估透射信号相位，并对预估透射信号相位求导获得信道时延特性。动态信道以正弦抖动等离子鞘套为研究模型，参照稳态预估算法并提取鞘套寄生调制对信号的影响，利用时变反射信号功率及幅度相关特性构建时变透射信号功率表达式，并求解概率密度分布获取时变信道下衰减特性。由于动态等离子鞘套对信号相位的同步调制，使反射、透射信号相位只与固定相差有关，对反射信号相位直接求解概率密度可反映时变信道下的时延特性。

(2) 设计出一套实时预估装置并进行硬件实现，预估装置设计包括微波前端电路中的反射信号提取方案，由ADS与CST的联合仿真对方案的可行性进行验证，另外数据处理方案由QuartusII软件编写核心算法并通过Modelsim仿真验证。实时预估装置的实现包括硬件平台搭建以及相关测试，其中硬件平台的搭建分为前端电路部分以及后端数据处理部分，前端电路部分硬件实现与微波前端电路模块设计原理一致，搭建完成后对该模块进行初步测试，后端数据处理部分主要由AD采集卡、FPGA开发板和计算机构成，利用数据处理核心算法主要对微波前端电路输出外部信号进行数据实时处理，搭建完成后对该系统进行整体测试。

(3) 针对预估装置对实时预估方法进行实验验证，主要通过将前端电路部分与数据处理部分相结合，进行稳态、动态等离子鞘套信道测量实验，并依靠预估方法对实验环境下鞘套信道特征进行实时预估，确定实验可行性以及预估方法的计算精度。

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 steady-state, 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 time-varying 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.