Optimum estimation and filtering of the ionospheric channel dispersion characteristics slope algorithms

Abstract

Data transfer in a broadband ionospheric radio channel is an actual problem currently. Ionospheric communication channel are characterized by non-stationarity, a hard interference situation, multipath propagation and dispersion distortion of signals. The frequency dispersion of the ionospheric channel is one of the most significant obstacles to the operation of decameter-band communication systems in a wide frequency band. Dispersion distortions of broadband signals lead to a significant deterioration in the characteristics of noise immunity of the radio link, a decrease in the probability of correct detection of signals in the air and synchronization problems with them. An important task is to estimate the parameters of the frequency dispersion of the ionospheric channel with the subsequent correction of dispersion distortions of broadband signals at the receiving point. Usually this problem is solved with the use of chirp-ionosondes as part of decametre communications. It is of interest to evaluate the parameters of the frequency dispersion of the ionospheric channel directly from the information broadband signal, without the use of the chirp ionosonde, and to ensure their tracking during the reception of information. The article compared the two methods of evaluating the slope of the dispersion characteristics of the ionospheric channel, probing its broadband signals - on the maximum likelihood criterion and the method of indirect estimation, through the evaluation of signal delays in the different sub-bands. There are formulas for calculating the dispersion of the estimates in the paper. Comparison of the calculated values and simulation showed that the method of division into sub-band yields not more than 2 in terms of standard deviation of the maximum likelihood method. Standard deviation of the maximum likelihood estimation varies from 7.5 to 2 us / MHz with an signal-to-noise ratio of 10 to 20 dB, whereas the standard deviation estimation method of division into sub-bands ranging from 15 to 4 us / MHz. The actual value of the slope is equal to 80 us / MHz. Formulas and an algorithm for optimal filtering of the slope of the dispersion characteristic of the ionospheric channel are obtained in the approximation of the linearization of the observation equation. It is assumed that the slope of the dispersion characteristic is a simple Markov random process.