Description: Radio communication in the decameter range is important in a special-purpose communication system. It provides users with the exchange of various kinds of information thousands of kilometers without broadcasting. The important features of radio channel are the frequency and time changes in its characteristics and the multipath extension of electromagnetic waves in the ionosphere. Given properties impose restrictions on the implementation of modern high-speed and wide-band transport systems in the decameter range. Thus, the ways of eliminating these deficiencies determine those areas in which it is possible to increase the efficiency of KH-radio communication. The most common message in air communication systems is language. During constructing these systems, it is necessary to solve the contradiction between the minimum allowable speed of translating the speech signal into a digital sequence and the maximum permissible speed of its transmission through the KH-radio line. These restrictions exist due to the features of the message broadcast and communications links. Due to the development of digital technologies and microelectronics, the creation of reliable and economical standard elements, it is possible to partially eliminate mentioned restrictions to the construction of modern radio stations. The work substantiates the expediency of digital processing of the speech signal parameters in its frequency plane. The gain at the speed of signal processing by the vocoder is determined with the change of signal parameters in the frequency plane that is significantly smaller in comparison with the time plane. The definition of the discrete speech signal spectrum on a modern element base is realized on the basis of Fast Fourier Transform (FFT). One of the known methods for transmitting digital signals through the limited-bandwidth radio communication lines is FBMC-Filter Bank Multicarrier technology that should be distinguished. The suppression of the side lobes of the signal by the FBMC filter bank is significantly greater than that of OFDM (Orthogonal Frequency Division Modulation)). This will improve the efficiency of using the frequency band and the noise protection of the radio channel. One of the further directions for improving the decameter range radio stations is the application of technologies that implement multi-position encoding of the radio signal using signal-code designs. This will increase the bandwidth of the radio link and partially improve its noise protection, based on the analysis of the signal-to-noise situation and adaptation to it. Thus, the main tendencies of improving the decameter range radio stations are: the use of parametric methods for processing telephone communications; realization of frequency-time signal processing; combined application of FBMC and multi-position radio signal coding using signal-code devices.
Keywords: radio communication, decameter range, radio signal, information processing, vocoder, envelope spectrum, discrete Fourier transform
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