Joint altitude, power control, and bandwidth allocation optimization for unmanned aerial vehicle-enabled reliable communications

Unmanned aerial vehicles (UAVs) as aerial relays have found many applications in the current communication network. Since the air-to-ground (AtG) link differs from the terrestrial link, ensuring a reliable AtG transmission remains to be a meaningful issue. This article investigates that a UAV works as an aerial relay to forward information from multiple access points to multiple remote base stations in an emergency situation. Using the full-duplex decode-and-forward relaying mode, we formulate a problem to minimize the maximum outage probability among all links, jointly optimizing the UAV altitude, power control, and bandwidth allocation. The outage probability function takes into account the line-of-sight probability-based AtG fading and the self-interference introduced by full-duplex relaying, both of which make our formulated problem nonconvex. We reformulate the outage probability function into a more tractable function. Then, we decouple the original problem into two subproblems, that is, altitude optimization as well as power control and bandwidth allocation. Each subproblem is solved by the successive convex optimization technique, and an overall iteration algorithm is proposed to solve the original problem based on the block coordinate descent theory. Simulation results reveal the reliability gain of our proposed algorithm compared with our designed benchmark. Besides, the optimal UAV three-dimensional location that minimizes the global min-max outage probability is found by numerical simulations. Finally, the average throughput gain can also be obtained by our proposed algorithm.