Spectral efficiency of signals of multichannel communication systems with orthogonal modulation

Abstract

The errors of restoration of original continuous signals in digital communication systems with orthogonal modulation of equidistant subcarriers (the so-called OFDM technology) are considered. The theory of radio circuits and signals is applied as a 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 for analysing composite signals with arbitrary selection of the sampling frequency of spaced subcarriers have been developed, and quantitative estimates of the quality of signal restoration on the receiving side have been obtained using the method of summing Fourier integrals according to Feuer. 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. In addition, it was established that the correct selection of the Feuer kernel and discretisation of OFDM signals allows increasing the accuracy of signal recovery on the receiving side and the overall efficiency of the wireless communication system due to the reduction of Gibbs pulsations energy. Spectral efficiency of signals, which are used in wireless communication systems, depends in great degree from correct choice of smoothing kernel. Also, with a dynamic change in the number of members of the decomposition series in wireless networks, the influence of frequency collisions, Gibbs ripples, and the level of intersystem interference is reduced. Comparative analysis of other smoothing factors, such as Lanzosh factor, two-parameter factor, etc. when decomposing in a series on a quasi-orthogonal system of basis functions shows that the errors of restoring the output signals depend on various influencing factors. It was also established that there couldn’t be a universal recipe for choosing a smoothing multiplier (or kernel). This problem requires additional research of an analytical and computational nature.