返回式航天器动态等离子体低频电磁波信道特性研究

Channel characteristics of dynamic plasma sheath around re-entry vehicles on low-frequency electromagnetic wave propagation

考虑低频电磁波在等离子体鞘套下强穿透能力,低频法被认为是一种缓解黑障影响的可行方法。现有研究建立了低频电磁波在稳态等离子体鞘套下衰减模型,但是忽略了动态等离子体信道对信号的影响,缺乏对该信道特性的深入认识。因此,对动态等离子体低频电磁波信道特性开展研究,以动态等离子体信道响应为基础,结合有色高斯分布时变电子密度模型,建立了动态等离子体信道统计模型,获得了该信道一阶统计特性,幅度概率密度函数P_(r)(r)为幂函数-高斯函数结合分布,相移概率密度函数P_(φ)(φ)为正切函数-高斯函数结合分布,功率谱密度函数S_(Hi)(ω)为有色噪声分布。为验证该信道统计模型有效性,开展多种状态的数值仿真(电子密度10^(18)~10^(19)/m^(3),碰撞频率1~5 GHz,低频电磁波频率1~30 MHz),仿真结果与理论结果高度吻合。随着电子密度从10^(18)/m^(3)增大10^(19)/m^(3),幅度、相移随机波动程度增强,P_(r)(r)均值μ_(r)从1.33增大至34.04,标准差σ_(r)从0.13增大至14.34;P_(φ)(φ)均值μ_(φ)从0.58增大至5.81,标准差σ_(φ)从0.11增大至1.19,功率谱发生衰减和展宽现象。刻画的动态等离子体低频电磁波信道,对低频通信调制算法设计和性能评估具有重要意义。

Low-frequency(LF)electromagnetic(EM)waves exhibit stronger transmission behavior under a plasma sheath,which has a positive impact on mitigating radio blackout.Previous work has established attenuation models for LF EM waves under the steady-state plasma sheath,but neglected the time-varying properties of the plasma,lacking an in-depth understanding of the channel characteristics.Therefore,this study focuses on the channel characteristics of dynamic plasma sheath on LF EM waves.The channel stochastic model of the dynamic plasma is established at LF EM wave bands,where the channel response of the dynamic plasma is merged with the colored-Gaussian time-varying electron density model.The first-order statistical properties of the dynamic plasma channel are obtained.The probability density function(PDF)of envelope P_(r)(r)is a power-Gaussian function,the PDF of the phase shift P_(φ)(φ)is a tangent-Gaussian function,and the power spectral density(PSD)function S_(H_i)(ω)is a colored noise function.To validate the effectiveness of the proposed channel statistical model,the muti-state numerical simulations are conducted,and the simulation results are in good agreement with the theoretical results.The electron density is 10^(18)-10^(19)/m^(3),the collision frequency is 1-5 GHz,and the frequency of LF EM waves is 1-30 MHz.When the electron density increases from 10^(18)/m^(3) to 10^(19)/m^(3),the degrees of random fluctuation on envelope and phase shift increase.The mean of P_r(r)increases from 1.33 to 34.04,and the standard deviation of P_r(r)increases from 0.13 to 14.34;the mean of P_φ(φ)increases from 0.58 to 5.81,and the standard deviation of P_φ(φ)increases from 0.11 to 1.19;the PSDs are attenuated and broadened.The results reveal the channel characteristics of dynamic plasma at LF EM wave bands,which is significant for designing LF communication modulation algorithms and evaluating the performance of LF communication systems.