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In this paper, we develop a wireless relay network model for an unmanned aircraft (UA) system, where an UA serves as a resilient moving relay among the ground stations with disconnected communication links in the event of disasters. A fixed-wing type is considered as our UA model, since it can operate longer than a rotary-wing UA without recharging battery, but the former can fly only in a circular manner and thus is difficult to stay at a fixed position. When the UA relays the received information to the destination with a conventional fixed-rate decode-and-forward protocol, the circular flight operation of a fixed-wing UA imposes a severe limitation on the achievable performance in terms of outage probability and information rate as they considerably depend on the location of the UA. Therefore, we propose a variable-rate relaying approach that enables us to optimize the achievable performance. Based on the theoretical derivation of the outage probability and formulation of its optimization process, we demonstrate that significant improvement over a conventional fixed-rate relaying can be achieved by the proposed rate optimization.
Ono et al. (Wed,) studied this question.