Non-Orthogonal Multiple Access for mmWave Drone Networks with Limited Feedback

Unmanned aerial vehicle (UAV)-aided wireless communication networks can be a smart solution to provide connectivity during temporary events and after disasters. However, achieving high spectral efficiency is of paramount importance for UAVs due to limited energy resources on board of a UAV. In this paper, we introduce non-orthogonal multiple access (NOMA) transmission for UAVs serving as aerial base stations (BSs) at a large stadium potentially with several hundreds or thousands of mobile users. In particular, considering millimeter-wave (mmWave) transmission, we make use of multi-antenna techniques to generate directional beams specifically taking into consideration the physical constraints of the antenna array. Multiple users are served simultaneously within the same beam employing NOMA techniques. We focus on a limited feedback scheme in which user distances are considered for user ordering during NOMA formulation. For each user participating in NOMA, a target rate based on their quality of service (QoS) requirements is defined and UAV-BS hovering altitude is optimized to serve more users at their requested target rates. We develop a comprehensive framework over which outage probabilities and respective sum rates are derived rigorously for the distance feedback mechanism, which are verified through extensive simulations. Our analytical and simulation results depict that NOMA with distance feedback can provide better outage sum rates compared to its orthogonal counterpart. We investigate the optimal operation altitude of UAV-BS to maximize the sum rates using the tools of developed analytical framework. The importance of identifying a proper user pair for maximizing sum rates with NOMA transmission is also investigated.