The method of GPS monitoring of small-scale inhomogeneities of the ionosphere and its application for predicting the noise immunity of satellite communication systems

Abstract

A method has been developed for GPS monitoring of small-scale fluctuations in the total electronic content of the ionosphere and using its results to predict changes in the noise immunity of satellite communication systems under ionospheric disturbances. To this end, the software of the GPStation-6 receiver of the global navigation satellite system was modified in the direction of replacing the code measurements of the total electronic content of the ionosphere with combined (code-phase) measurements, which practically eliminates the "noise" component of the measurement error. To separate small-scale fluctuations of the total electronic content from large-scale ones, it is proposed to use a 6th-order digital Butterworth filter, which in the transmission frequency range (1-10 Hz) at a sampling frequency of 50 Hz provides an amplitude-frequency response close to ideal and introduces a delay not exceeding the permissible value. An expression is obtained for calculating the output samples of this digital filter. The obtained results of estimating small-scale fluctuations of the total electron content of the ionosphere at the output of the digital filter allow us to estimate the standard deviation of these fluctuations. On this basis, the results of calculating the ionospheric flicker index of the received signals of satellite communication systems are obtained. This makes it possible to predict the probability of their erroneous reception at a given average value of the signal-to-noise ratio at the input of the satellite receiver. Analysis of the obtained results of predicting the noise immunity of satellite communication systems shows that in the conditions of an undisturbed mid-latitude ionosphere, the probability of erroneous reception may exceed the permissible value for 30 seconds. This confirms the assumption that with small-scale disturbances of the ionosphere, the probability of error in satellite communication systems may exceed the permissible value for a long time.