engleski

Doppler effect in non-GSO satellite propagation

Ground based satellite user terminals face with significant frequency Doppler shift in downlink direction,communicating with non-geostationary satellites, caused by the line of site component of the relative velocity vector. The paper deals with analytic derivation of frequency Doppler shift measured by a user on the surface of the Earth, and possible application of this phenomenon for satellite navigation system. Previous research mainly focused on efficient methods for compensation of this effect. The novelty of this paper is, that it gives mathematical derivation of the frequency Doppler shift observed by the terminal situated anywhere on the Earth, from non geostationary satellite using inclined circular orbit. Based on this, LOS relative velocity component is calculated, and S-shaped frequency shift – time curves are derived(with maximum elevation angle as parameter). Two major fields of application are: analytic frequency shift estimation can be used for Doppler effect compensation in the terminal’s processor, or frequency Doppler shift effect can be used for estimating the position of relatively slow moving terminal (e.g. land transportation, maritime, search and rescue missions, customer applications). Measuring the slant of frequency shift - time change, observing the moment of zero frequency shift and measuring the transit time of the signal from the satellite to the user terminal it is possible to calculate elevation, azimuth and distance. Based on this, three values Cartesian coordinates of the terminal are calculated determininfg its position.

non-GSO satellite; Doppler effect; satellite navigation and positioning; satellite propagation

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