This paper considers and characterizes a multiple access relay channel (MARC) with $k$ transmitters, one UAV relay, and a terrestrial receiver, where we derive a new achievable rate region for the continuous alphabet wireless with an unmanned aerial vehicle (UAV) relay. The derived rate region is then evaluated numerically and compared with those of multiple access channels (MAC) and MARC with terrestrial relays. The results show that the presence of a UAV relay increases the achievable rate region of MAC systems by exploiting higher line-of-sight (LoS) channel quality and time-varying spatial link gains due to the UAV’s position. This improvement in the achievable region is not merely due to the UAV’s presence but arises from the different channel geometry and dynamic link conditions introduced by the UAV relay compared with terrestrial relays

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