CONSIDERATION OF PHASE DISTORTIONS CAUSED BY THE MOVEMENT OF GEOSTATIONARY REPEATERS WHEN LOCATING GROUND-BASED RADIO EMISSION SOURCES

Abstract

Currently, there are often cases of illegal use of the resource of relay satellites located in geostationary orbit, and the creation of unintentional and deliberate interference with legal users of satellite communication systems, for example due to non-compliance with the power standards of radio transmitting devices and antenna radiation patterns, as well as the rules for the frequency spectrum regulating. One of the possible stages of the response by the radio frequency service and satellite systems operators to such situations may be an operational assessment of locating of the interference ground radio emission sources that violate the established requirements. The existing methods for estimating the coordinates of radio emission sources operating through geostationary satellites-repeaters involve calculating the Cross-Ambiguity Function (CAF) of signals received from several satellites that relay the signals of the main and side lobes of the antenna pattern of the geolocated source. In the case of a low received signals SNR, it is required to record signals for a long time, and in such cases, to achieve a sufficient SNR at the correlator output, it is necessary to take into account not only the Doppler frequency shift between the signals, but also the change in the frequency shift caused by the change in the velocity vectors of the repeater satellites. The aim of this work is to study the recording duration, at which it is required to take into account phase distortions caused by a change in the speed of the repeater satellite and their effect on the SNR at the correlator output, as well as to develop a method for accounting for such distortions. The theory of digital signal processing and the method of simulation were used as research methods. As a result of the study, an assessment was made of the duration of the signal recording, at which the Doppler frequency shift can be considered constant; introduced the concept of a modified CAF, which takes into account the change in the Doppler frequency shift due to its approximation by a linear function; the maximum duration of signal recording was estimated, at which the proposed linear approximation is valid. It is concluded that in the case of using the modified CAF, the minimum duration of signal recording, at which the absence of correlator output SNR degradation will be guaranteed, is 8.1 times greater than when using the traditional CAF.