Altitude Optimization for DF Relaying Trajectory of UAV in Cooperative FANET

Advent of unmanned aerial vehicle (UAV) as relay in ad-hoc networks has offered numerous promising communication solutions with both military and civilian applications. Additionally with more degrees of freedom, mobile UAV relaying provides better susceptibility to changing environment conditions thereby enhancing the network performance. However, optimization of UAV altitude is a primary concern in such flying ad hoc networks (FANETs). In this work, we consider a three node decode-and-forward (DF) FANET, and the aim is to minimize the average network outage probability subject to practical mobility constraints of maximum UAV velocity and minimum allowable UAV height, thereby finally optimizing the overall UAV trajectory (UT). In particular, for pre-determined initial and final relay positions, we first prove convexity of the optimization problem and then obtain the semi-closed-form globally optimal UT solution. The analysis is numerically validated along with the discussion of multiple optimal design insights. Results reveal the respective average performance gain of 56% and 37% over the two benchmark schemes.