Asymptotic characteristics of multichannel access systems with orthogonal filteration

DOI: 10.31673/2412-9070.2022.024045

Abstract

The proposed article deals with digital modulation schemes that use a certain number of equidistant orthogonal subcarriers (the socalled OFDM technology). The theory of radio engineering chains and signals is used as the scientific and technical basis of the problem. The spectra of discrete signals were analysed, the influence of violations of the conditions of Kotelnikov's theorem and the asymptotics of the recovery errors of the original continuous signals were investigated. Methods of forming composite signals with arbitrary frequency difference of subcarriers have been developed. It is shown that when the amount of frequency shift of the basic series decomposition functions and the width of the spectrum of the main and side lobes in the spectrum of the output signal are matched, it is possible to count on the minimal influence of mutual interference and intersymbol interference of the composite signal. It was established that the method of orthogonal frequency multiplexing of channels (OFDM) allows to significantly increasing the bandwidth of the wireless communication system. In addition, with dynamic load changes in wireless networks, the impact of frequency collisions and an increase in the level of intra-system interference is minimized. Graphical analysis of the results of the series expansion on the quasiorthogonal system of basis functions shows that the errors of restoration of the original signals can reach unacceptable values. It was also established that when expanding into a non-orthogonal series with a larger number of members, the situation with the restoration of the original signals becomes a little more suitable, but no guarantees of monotonous improvement of the situation with restoration errors can be given in principle. This problem requires additional analytical research.

Keywords: OFDM technology; the theory of radio technical contours and signals; Kotelnikov's theorem; restoration errors of initial signals.

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