时变等离子鞘套相位抖动对GPS导航的影响

飞行器再入过程中产生的时变等离子鞘套会引起信号的时变衰减和相位抖动,其产生的相位抖动对调相体制的GPS导航系统必然产生影响。探讨了时变等离子鞘套引起信号相位抖动的机理，通过传输矩阵法计算了由时变等离子鞘套引起GPS导航信号的相位抖动的统计特性，结合Hilbert方法建立了受到相位抖动影响的GPS信号模型，研究了黑障发生前等离子鞘套的相位抖动对GPS导航的影响。仿真结果表明GPS导航受到影响的程度和相位抖动方差大小密切相关。在NASA数据下相位抖动方差为0.1142时，定位变化大于10m的最大比例超出了1.5%，大于5m的最大比例超出了14%。

Effect of Time Varying Plasma Sheath Phase Fluctuation on GPS Navigation

The time varying plasma sheath can potentially degrade electromagnetic systems through increasing time varying amplitude attenuation and phase fluctuation. The BPSK modulated GPS signals could be affected by phase fluctuation. Utilizing electron density and collision frequency provided by NASA, transmission coefficient is calculated by using the scattering matrix method and phase fluctuation characteristic is obtained. GPS signal affected by phase fluctuation are acquired by the Hilbert method. Then by means of Electromagnetic propagation theory and GPS software receiver, the effects of phase fluctuation caused by plasma sheath on GPS signal and its positioning before there occurs blackout are analyzed. Results show that the effect on positioning accuracy is closely related to the variance of phase fluctuation. When the calculated variance is 0.1142, the maximal percentage of variation larger than 5m is up to 14% and the percentage larger than 10m is up to 1.5%.