"Networks whereby traditional terrestrial users (TUs) coexist with flying unmanned aerial vehicles (UAVs) acting as additional aerial users (AUs), has gained significant attention as a promising technology for future 5G and beyond networks. In this scenario, we investigate the case wherein an UAV and a static TU are paired to simultaneously transmit their uplink signals to a ground base station (BS) in the same time-frequency resource blocks. The signal transmitted by the AU experiences both time dispersion due to multipath propagation effects and frequency dispersion caused by Doppler shifts, whereas the signal transmitted by the static TU is subject to multipath effects. To decode the superposed signals at the BS, we propose a novel sky-ground (SG) nonorthogonal multiple access (NOMA) receiving structure that additionally exploits the different circularity/noncircularity and almost-cyclostationarity properties of the AU and TU through time-varying successive interference cancellation."
 

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