Fairness-Aware Closed-Form UL-DL Power Allocation for NOMA in UL Heavy UAV Systems

In this paper, we investigate an unmanned aerial vehicle (UAV) assisted communication system for uplink (UL) heavy scenarios such as a football match, where intensive video uploading from the audience is demanded. Non-orthogonal mul-tiple access (NOMA) is exploited to enhance system throughput, while it suffers a dynamic user rate gap within each NOMA group due to UAV movement. In light of the user fairness issue and the UL heavy demands, we propose joint UL-DL optimization of user scheduling, power allocation (PA) and UAV trajectory (JOSPT). In particular, closed-form optimal solutions are derived for dynamic PA in both UL and DL, which plays a dominant role in system performance. The proposed PA scheme is more effective in maintaining user fairness than the previous work and also computationally efficient and suitable for energy-limited UAV system. The average spectrum efficiency of the proposed NOMA UAV system in UL and DL is also much higher than that of the orthogonal multiple access (OMA) based UAV system, with the heterogeneous rate demands accommodated.