Abstract
The paper considers the solution to the problem of increasing the spectral efficiency of a digital transmission system with multifrequency modulation and optimal finite signals that do not cause intersymbol interference in various channels of a multifrequency modem. Applying the method of multi-frequency data transmission based on two-dimensional signal processing, high-speed data transmission is organized over frequency-limited communication channels based on wired technologies of the xDSL standard. The well-known and new modem, which is superior in efficiency to similar modems, are presented. In this paper, the modernization of a multifrequency modem with optimal finite signals based on quadrature amplitude modulation (QAM) is considered. The peculiarity of this structure is as follows: the use of new, synthesized optimal finite OFS-2 signals with increased noise immunity; in the application of the new structure of the multi-frequency modem MFM3; in the use of a frequency-limited GCS in the UEP DCS at the reception in order to compensate for the amplitude and phase distortions introduced by it. Comparative results of calculations of the spectral-energy efficiency of the considered multi-frequency modulated modem MFM3 with OFS-2 and narrow-band subcarriers are illustrated by the graphs in Fig. and presented in Table . Implementation of the new modem in digital telecommunications systems will significantly increase their spectral efficiency. The proposed approach can be used to organize high-speed data transmission over frequency-limited communication channels based on wired technologies of the xDSL standard. For the first time, an adaptive multi-channel digital transmission system with a new multi-frequency modem and new optimal second-type finite signals with increased spectral and energy efficiency has been developed, taking into account optimal estimates of the parameters of the direct communication channel transmitted via the feedback channel and used both in transmission (in the modulator) and reception (in the demodulator).
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