UAV-Enabled Reliable Mobile Relaying Based on Downlink NOMA

Abstract

Unmanned aerial vehicle (UAV) relaying is an efficient solution to provide wireless access for emergency communications due to the high flexibility. The system reliability is usually constrained under limited bandwidth and power resources. Downlink non-orthogonal multiple access (NOMA) can improve the system reliability through a higher resource utilization. To this end, we introduce downlink NOMA to a UAV-enabled mobile relaying system and investigate a scenario where a fixed-wing UAV flies in a circular trajectory to serve as a mobile decode-and-forward (DF) relay in an emergency situation. Since guaranteeing a reliable link is necessary in an emergency situation, our formulated problem is to minimize the maximum outage probability among all links, taking into account the bandwidth and power allocations based on downlink NOMA. Specially, the condition for successful successive interference cancellation (SIC) is also considered. By making change of variables and introducing slack variables, we reformulate our problem into a more tractable form, then we propose an iteration algorithm to solve our problem based on the successive convex optimization (SCO) technique. The optimized bandwidth and power allocation schemes as well as the min-max outage probability along the UAV trajectory are obtained, respectively. Two benchmarks are designed to reveal the performance of our proposed algorithm, and the reliability gain can be obtained by comparing the min-max outage probability and the overall average outage probability. INDEX TERMS UAV, mobile relaying, downlink NOMA, outage probability, resource allocation. I. INTRODUCTION A. BACKGROUND AND MOTIVATION

Uplink and Downlink NOMA Transmission Using Full-Duplex UAV

“…Therefore, communication services are still be served in an emergency situation by enabling a UAV serving as an aerial relay. In particular, the authors in [26]- [33] investigated promising applications related NOMA , UAV, vehicle to everything (V2X). For example, [26] studied NOMA-enabled mobile relaying.…”

“…In particular, the authors in [26]- [33] investigated promising applications related NOMA , UAV, vehicle to everything (V2X). For example, [26] studied NOMA-enabled mobile relaying. In their study, to serve as a mobile decode-and-forward (DF) relay, a fixed-wing UAV flies in a circular trajectory to guarantee a reliable link.…”

“…Indeed, very few works studied the performance of FD-NOMA scheme for UAV system over the Nakagamim fading channel. Although [26], [27] considered uplink downlink NOMA-assisted UAV system, however it is necessary to investigate the fundamental impact of communication channel on the performance of UAV system over Nakagamim channel. Therefore, this paper provides a general framework to design uplink downlink NOMA-assisted UAV in practice.…”

Gateway Selection in Millimeter Wave UAV Wireless Networks Using Multi-Player Multi-Armed Bandit

“…In [21], a new UAV node placement technique for multi-UAV relay communication was solved based on the non-linear constraint optimization problem. The authors in [22] introduced downlink non-orthogonal multiple access (NOMA) to a UAV-enabled mobile relaying system.…”

“…In these fully decentralized settings, no prior information is either available or exchanged among UAVs. Despite its realism, this problem is unique and utterly different from the existing UAV gateway/relay selection problems [17][18][19][20][21][22], where UAVs can easily exchange information among them through the fully connected UAV network. Data rates among UAVs can also be anticipated beforehand via prior channel measurements and estimations.…”