Energy Efficient AAV-Assisted Bidirectional Relaying System for Multi-Pair User Devices

Autonomousaerial vehicles (AAVs), or drones, are garnering considerable focus in the realm of wireless communications research because to their notable characteristics, including exceptional mobility, versatile deployment capabilities, and robustness in maintaining line-of-sight (LoS) links. This paper studies a AAV-assisted bidirectional relaying system for multi-pair user devices (UDs), where a rotary-wing AAV is used to serve as a mobile relay for providing information transmission between UDs belonging to a pair on the ground. The UDs in a pair communicate with each other via the AAV relay employing the physical-layer network coding (PNC) technique. To trade off fair communications with system energy consumption, we jointly optimize transmission scheduling and association, AAV relay and UD transmission power, and AAV trajectory to maximize system energy efficiency during AAV relay communications. Due to the formulated problem being mixed-integer and nonconvex programming, it proves to be excessively complex to solve. For ease of solution, this problem is initially decomposed into three sub-problems. Next, by adopting the block coordinate descent (BCD) method, the successive convex approximation (SCA) method, and the Dinkelbach method, an efficient iterative algorithm is proposed that alternately solves variables of each sub-problem while fixing others. The numerical results demonstrate that our designed scheme is capable of substantially improving the system energy efficiency in comparison with other baseline schemes and benchmark schemes.