The Research On GPS Acquisition And Tracking Under The Plasma Sheath

A high-speed spacecraft entering the Earth’s atmosphere can generate seriousfriction, causing the air around the vehicle ionized, and then resulting in the so-calledplasma sheath. The sheath will case the attenuation, refraction and scattering ofelectromagnetic waves and hamper the communication and navigation of the vehicle.This paper analyzes the influences of the plasma sheath on GPS navigation signals andmethods to decrease or even cancel the influence of plasma sheath from improving theway of signal processing.The paper is organized as follows. First of all, the paper introduces and realizes themain content of GPS signals, and then adds the plasma sheath model. The paper studieson the theoretical analysis and simulation calculations of the influences of the plasmasheath on the GPS signals. The impacts include amplitude attenuation, phase shift andtime-varying character. Doppler shift is unavoidable because of high-speed relatingmoving between the satellites and the spacecraft.Finally, signal acquisition and tacking simulation is realized in the presence andabsence of the plasma sheath model. In the stage of acquisition, a new acquisitionalgorithm which is aimed at plasma sheath based on the combination of coherent andnon-coherent integration is proposed. The algorithm works with-34dB/2MHz signals.This is followed by a description of other algorithm. In the stage of tracking, animproved digitization of the C/A code is realized, attaining the influence of the plasmasheath on the tracking and the whole procedure. The algorithm works with-36dB/2MHz.The improvement of acquisition and tracking algorithm can reduce theblackout to some extent, but cannot completely eliminate.