Delay-Doppler Robust Spectrum Sharing of UAV and Terrestrial Systems Aided by Assistive Slots

A delay-Doppler robust spectrum sharing method is proposed for the unmanned aerial vehicle (UAV) and terrestrial systems by actively introducing the assistive slots (AS) in this work. With the aids of AS, the receiver in the UAV/terrestrial link can extract the delay-Doppler parameter of the signal, and hence further recover the desired signal. Inserting AS in frames introduces different possibilities of signals sampled at AS and non-AS points, and the UAV/terrestrial signal samples are differentiated from the compound signals by focusing on the energy gap among the samples. Since the signal sample differentiation and the delay-Doppler parameter extraction are receiver oriented, the effects of multipath and node mobility are included, and the signal recovery is free from the adverse impacts of delay and Doppler shifts. Analysis shows that although introducing AS is beneficial to recovering the UAV/terrestrial signal, the signal transmission efficiency suffers degradation. Therefore, the optimal AS ratio regarding the tradeoff between delay-Doppler parameter extraction accuracy and transmission efficiency is investigated. For the optimal AS ratio, the signal-to-interference ratio of the spectrum sharing system plays a key role under Rician/Rayleigh distributed terrestrial fading channels. The numerical results validate the effectiveness of the proposed scheme in comparison to the traditional methods.