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We investigate the maneuvering control of a UAVbased relay for efficient communication with mobile ground nodes. The objective of the maneuvering control is to maximize the minimum ergodic link capacity which is achieved by any ground node. We propose an efficient maneuvering control scheme of a UAV-based relay which does not require any location or direction information of ground nodes. The proposed control scheme exploits the received signal strengths (RSSs) from ground nodes but it dose not need a channel model to estimate the location of ground nodes. Therefore, the proposed control scheme significantly reduces the communication overhead and/or computational complexity while achieving similar performance, compared with that of an optimal scheme which requires the location information of ground nodes.

We focus on energy-aware path planning of a small unmanned aerial vehicle-based relay which forwards the data received from a stationary remote station to a mobile access point. In order to reduce the communication power required for reliable communication between the unmanned aerial vehicle-based relay and access point, the unmanned aerial vehicle-based relay keeps track of the access point within a maximum allowable horizontal distance at a constant altitude, and thus the communication power of the unmanned aerial vehicle-based relay decreases as the horizontal distance decreases. In order to determine the energy-efficient manoeuvring of the unmanned aerial vehicle-based relay within the horizontal distance, we formulate a new off-line trajectory optimization problem. The solution of the problem gives insight into how to realize the energy-efficient manoeuvring. For online implementation of energy-efficient path planning (manoeuvring control), we propose two control schemes: a model predictive control scheme and a standoff tracking control scheme. These schemes can significantly reduce manoeuvring energy compared with conventional schemes.