This letter studies the energy-efficient unmanned aerial vehicle (UAV) communications to support ground nodes (GNs). The system considers the UAV working as a relay while there is a base station (BS) on the ground. We analyze the UAV energy consumption model to design the energy-efficient UAV trajectory path. We formulate the energy-efficient UAV relaying communication, which considers both throughput and UAV propulsion energy consumption. We optimize joint transmit power of UAV and BS; UAV trajectory, acceleration, and flying speed to maximize the energy-efficient UAV relaying problem. We also introduce a constraint named as information causality constraint (ICC). The main idea of ICC is to guarantee that the UAV receives information from BS in any time slot and forward the only received information to GNs in remaining time slots. The formulated energy-efficiency maximization problem is not convex. Thus, we solve it sub-optimally using the iterative method. Finally, we present the simulation results to validate the efficacy of the proposed algorithm.

中文翻译：

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为地面节点服务的节能无人机中继通信

这封信研究了支持地面节点 (GN) 的节能无人机 (UAV) 通信。该系统将无人机视为中继，而地面上有基站（BS）。我们分析无人机能耗模型以设计节能无人机轨迹路径。我们制定了节能无人机中继通信，它考虑了吞吐量和无人机推进能耗。我们优化了无人机和基站的联合发射功率；无人机轨迹、加速度和飞行速度最大化节能无人机中继问题。我们还引入了一个名为信息因果关系约束（ICC）的约束。ICC 的主要思想是保证 UAV 在任何时隙接收来自 BS 的信息，并在剩余的时隙将仅接收到的信息转发给 GN。公式化的能源效率最大化问题不是凸的。因此，我们使用迭代方法次优地解决它。最后，我们给出了仿真结果来验证所提出算法的有效性。