Energy-Efficient Communications in Solar-Powered Unmanned Aerial Systems

Abstract

An unmanned aerial system (UAS), consisting of unmanned aerial vehicles (UAVs) with wireless transceivers, has been considered as an indispensable complement to conventional terrestrial communication infrastructure that cannot fully meet mobile users' demand on ubiquitous connectivity, particularly in some practical areas, such as complex terrains, disaster areas, and temporary traffic hotspots. Thanks to UAVs' high maneuverability and flexible deployment, a UAS can be deployed in these areas to offer ubiquitous connectivity in a timely and cost-effective way. However, due to the limited onboard energy storage capacity, UAVs have to frequently land for energy replenishment, which inevitably affects the provisioning of wireless connectivity services. To prolong UAVs' hovering time, adopting solar energy to power them is an alternative way. In this paper, we explore the joint control of routing, data rate, and transmission power to minimize the energy consumption rate of relaying data in solar-powered UASs. The energy consumption rate minimization problem is formulated as a nonlinear programming (NLP), which is generally NP-hard. To efficiently solve the formulated NLP, we develop an ∊-bounded approximation algorithm that employs a piece-wise linear approximation approach to approximate its nonlinear term and thus reformulate the original problem as classic linear programming (LP). Particularly, we find a theoretical performance gap that is bounded by the approximation error ∊. We conduct extensive simulations to show significant performance improvement.