UAV Relay Altitude Optimization Strategy for Minimizing Outage Probability

Unmanned aerial vehicle (UAV) has been widely used in wireless communication systems because of their mobility and flexibility. In this paper, we consider an UAV relay system to assist wireless transmission from the base station to the user. Different from ground communication, the UAV communication channel is an air-to-ground channel, and its line-of-sight (DoS) transmission component is larger. For the UAV air-to-ground channel model, we consider both large-scale fading and small-scale fading. The large-scale fading adopts the probabilistic DoS channel model, and the small-scale fading adopts the Rician fading model. In order to improve the UAV communication performance, we propose a relay altitude optimization strategy based on the minimization of outage probability, and derive the approximate expression of the optimal altitude. Simulation results illustrate that the altitude optimized algorithm proposed in this paper can greatly decrease the system outage probability.