Aiding a Disaster Spot via an UAV-Based Mobile AF Relay: Joint Trajectory and Power Optimization

Followed by the destruction of existing infrastructure or the emergence of the necessity for a new infrastructure, disaster events (e.g., earthquakes and pandemic) may require inspection of certain area and passing information to a dedicated help unit. Unmanned Aerial Vehicle (UAV)-aided mobile relaying technology is one of the effective means of provisioning service in such situations. In this paper, as the part of the rescuing operation in a certain disaster spot, we consider a mobile relaying technique, where an UAV acts as a relay node to ferry data between two disconnected floating or fixed nodes. For the sake of simplicity and low cost, amplify-and-forward relaying capability is adopted for the UAV. We consider the maximization of end-to-end throughput of such a system by optimizing the source/UAV power allocation as well as the trajectory of the UAV while considering practical mobility constraints (on the speed and initial/final locations of the UAV) as well as signal causality constraints. The formulated optimization problem is non-convex, and hence intractable to solve. Therefore, similar to the existing solution approach, we solve the problem via an iteration-based solution strategy, however we solve the source/UAV power allocation and the UAV trajectory design problems per iteration in a different manner. For the source/UAV power allocation problem, we provide heuristic solutions while considering both the availability and absence of a buffer at the UAV node. On the other hand, for the given power assignment, we adopt the geometric programming (GP)-based approach upon the transformation of variables and constraints. Furthermore, under the free initial and final UAV locations, jointly optimal power allocation and UAV trajectory are derived. Through extensive simulation, we verify the effectiveness of the proposed scheme while comparing with one existing work.