Modern unmanned aerial vehicles (UAVs) are used in many spheres of human activity. In conditions of strong urban development, the radio communication channel with UAV is multi-path, which leads to a significant decrease in the quality of the transfer of useful information. Ensuring reliable and qualitative communication depends on the correct choice of the frequency range and the type of modulation used. Multiposition signals of M-PSK, M-QAM, M-FSK formats are considered. Due to the complexity of the mathematical description of such a radio channel, a computer simulation method was used to obtain the results. A multipath propagation model with a number of beams up to 10 is used. The dependencies of the probability of erroneous reception of information on the parameters of the communication channel are obtained: the signal-to-noise ratio, the number and intensity of the propagation paths. The energy parameters of the radio channel are calculated and the optimal frequency range is estimated from the maximum signal-to-noise ratio. It is indicated that the best in this criterion is the operating frequency range of 2-5 GHz. Calculations showed that the transmission coefficient of the radio channel is unstable and varies greatly in frequency. When using narrow-band signals M-PSK, M-QAM, this can lead to a situation where the signal can get into the "bad" frequency band and the quality of information transfer will decrease significantly. In connection with this, a radio channel with multiposition frequency modulation M-FSK was studied, when the transmission of discrete information is carried out using multiple parcels with different frequencies falling into both "bad" and "good" frequency zones. The results of the study showed that the probability of BER error in some cases improves by times compared to M-PSK and M-QAM. This allows us to talk about the prospects for the M-FSK format. Considering the good performance of this format, further studies are planned in the direction of using M-FSK format signals and their prospective version of M-CPFSK (multi-position frequency modulated signals with a continuous phase) in the considered radio channel with different modulation and positioning indices, in particular CPFSK with modulation indices of 0.5 and 0.75, together with MIMO and OFDM systems. The obtained results can be used in the design of modern and promising UAV-to-ground communication systems.
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