未来跨域飞行器面临多次重返大气层的过程，飞行器在大气层中以高超声速飞行时表面被等离子鞘套包覆，其带来的“黑障问题”将一直困扰着飞行器的可靠信息传输。等离子鞘套信道具有快时变特性，这种快时变特性导致通信符号经历随机深衰落，并且使得接收机难以实时跟踪信道系数的变化，对测控通信系统的可靠传输带来了巨大的挑战。针对上述问题，本文针对等离子鞘套信道时变特性中的相干时间进行了研究。本文首先分析了等离子鞘套信道动态特性的致变因素，并建立了动态等离子鞘套信道模型，然后设计了基于接收信号包络的信道相干时间计算方法，最后进行了仿真分析与实验验证。结果表明，信道相干时间与等离子体激励频率呈反比关系，且随载波频率增大呈现先减小后增大的趋势。通过调整码元速率与相干时间的相近程度，在电子密度值为1×1018 m?3条件下，根据计算所得的相干时间设定合适的码元速率可以为系统带来两个数量级的误码率性能提升。等离子鞘套信道相干时间的计算结果，可以为后续的通信方案设计提供一定的参考。
In the future, reentry vehicles will face multiple atmospheric reentry processes. During hypersonic flight through the atmosphere, the vehicle is enveloped by a plasma sheath, and the "radio blackout" caused by this sheath will con-tinue to hinder reliable information transmission. The plasma sheath channel exhibits fast time-varying characteris-tics, which result in communication symbols experiencing random deep fades and make it challenging for the re-ceiver to track the channel coefficients in real-time. This presents a significant challenge to the reliable transmis-sion of telemetry and control communication systems. To address these issues, this paper investigates the coher-ence time of the plasma sheath channel's time-varying characteristics. The paper first analyzes the factors contrib-uting to the dynamic characteristics of the plasma sheath channel and establishes a dynamic plasma sheath chan-nel model. Then, a method for calculating the channel coherence time based on the received signal envelope is designed, followed by simulation analysis and experimental validation. The results show that the channel coher-ence time is inversely proportional to the plasma excitation frequency and exhibits a trend of decreasing and then increasing as the carrier frequency increases. By adjusting the symbol rate to match the coherence time, an appro-priate symbol rate can be set based on the calculated coherence time under an electron density of 1×10^18 m?3, resulting in a two-order-of-magnitude improvement in bit error rate performance. The calculation of the plasma sheath channel coherence time can provide valuable references for future communication scheme designs.
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