Abstract
Recently, interest on the utilization of unmanned aerial vehicles (UAVs) has aroused. Specifically, UAVs can be used in cellular networks as aerial users for delivery, surveillance, rescue search, or as an aerial base station (aBS) for communication with ground users in remote uncovered areas or in dense environments requiring prompt high capacity. Aiming to satisfy the high requirements of wireless aerial networks, several multiple access techniques have been investigated. In particular, space-division multiple access (SDMA) and power-domain non-orthogonal multiple access (NOMA) present promising multiplexing gains for aerial downlink and uplink. Nevertheless, these gains are limited as they depend on the conditions of the environment. Hence, a generalized scheme has been recently proposed, called rate-splitting multiple access (RSMA), which is capable of achieving better spectral efficiency gains compared to SDMA and NOMA. In this paper, we present a comprehensive survey of key multiple access technologies adopted for aerial networks, where aBSs are deployed to serve ground users. Since there have been only sporadic results reported on the use of RSMA in aerial systems, we aim to extend the discussion on this topic by modelling and analyzing the weighted sum-rate performance of a two-user network served by an RSMA-based aBS. Finally, related open issues and future research directions are exposed.
Highlights
D UE to the unprecedented growth of mobile data traffic and stringent quality-of-service (QoS) requirements, recent research efforts have focused on several key enabling technologies for 5G networks and beyond [1], such as millimeter waves, terahertz (THz) communications, multiple-input multiple-output (MIMO), massive MIMO, multiple access techniques, relaying, cognitive radio, and unmanned aerial networks [2]
unmanned aerial vehicles (UAVs) can be deployed as aerial base stations to provide wireless access to ground and aerial devices/users, in several scenarios such as temporary events, disasters when a terrestrial cellular network is not fully operational, and congestion due to unpredictable traffic surges, as well as aerial devices/users [5], [6]
In frequency-division multiple access (FDMA) and orthogonal FDMA (OFDMA), different frequency bands or subcarriers are assigned to users, whereas in code-division multiple access (CDMA), by contrast, orthogonal codes are assigned to different users
Summary
D UE to the unprecedented growth of mobile data traffic and stringent quality-of-service (QoS) requirements, recent research efforts have focused on several key enabling technologies for 5G networks and beyond [1], such as millimeter waves (mmWave), terahertz (THz) communications, multiple-input multiple-output (MIMO), massive MIMO, multiple access techniques, relaying, cognitive radio, and unmanned aerial networks [2]. Mobility, agility, and high line-of-sight (LoS) probability, to offer strong non-terrestrial communication links to mobile users with versatile quality of service requirements [7], [8]. These additional degrees of freedom cannot provide the best communication experience to users of largescale cellular networks. VI Open Issues and Research Directions VI-A Joint Optimization of UAV and RSMA Parameters VI-B Integration of RSMA into MIMO, Massive MIMO, and mmWave Aerial Systems VI-C Distributed and Cooperative RSMA in Hybrid Terrestrial/Non-terrestrial Networks VI-D Physical Layer Security Issues in Aerial Multiple Access Networks
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