Airborne communications nodes are often proposed as a component in future communications networks. This paper proposes that, in any ground network served by such a node, there is an optimum location for an airborne communications node. The paper examines the example of a Medium Altitude/Long Endurance (MALE) UAV carrying an airborne communications node which supports a community of mobile subscribers. Consider the case of a power-limited communications payload being flown on a UAV in support of a large community of mobile subscribers. Each subscriber is connected to the UAV payload by a two-way radio link. Radio links are only activated when there is traffic to be exchanged, thus the RF power demanded from the payload is changing regularly. An algorithm has been developed which attempts to maximize coverage of the subscriber community by moving the UAV between waypoints at which coverage is maximized. The algorithm, called Select Locally Optimum Waypoints (SLOW), estimates the future locations of subscribers from historic traffic and location data, and uses this information to move to waypoints at which the greatest number of links can be supported within the available RF power, and to the required signal quality. This improves the overall coverage of the subscriber community. This paper considers the performance of the algorithm in different conditions. Initially the performance of the algorithm is assessed against the maximum RF power available from the payload. The paper considers the case where all subscribers are given equal weighting, and then addresses the case where 20% of subscribers are given priority access to the payload. The paper also considers how the algorithm responds to different traffic patterns and concludes with a brief assessment of the airspace implications of allowing the UAV to track the mobile subscribers.
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