The application of unmanned aerial vehicles (UAVs) to emerging communication systems has attracted a lot of research interests due to the advantages of UAVs, such as high mobility, flexible deployment, and cost-effectiveness. The UAV-carried base stations (UAV-BS) can provide on-demand service to users in temporary or emergency events. However, how to optimize the communication performance of a UAV-BS with a limited-bandwidth wireless backhaul is still a challenge. This paper focuses on improving the spectrum efficiency of a UAV-BS while guaranteeing user fairness under in-band backhaul constraint. We propose to maximize the minimum user rate among all the users served by the UAV-BS by jointly optimizing the allocation of bandwidth and transmit power, as well as the trajectory of the UAV-BS. As the formulated problem is non-convex, we propose an efficient algorithm to solve it suboptimally based on the alternating optimization and successive convex optimization methods. Computer simulation results show that the proposed algorithm achieves a significantly higher minimum user rate than the benchmark schemes.

由于无人机的高度机动性，灵活部署和成本效益等优点，无人飞行器（UAV）在新兴通信系统中的应用吸引了许多研究兴趣。携带无人机的基站（UAV-BS）可以在临时或紧急事件中向用户提供按需服务。然而，如何利用有限带宽的无线回程来优化UAV-BS的通信性能仍然是一个挑战。本文致力于在保证带内回程约束下的用户公平性的同时，提高UAV-BS的频谱效率。我们建议通过联合优化带宽和发射功率的分配以及UAV-BS的轨迹，在UAV-BS服务的所有用户中最大化最小用户速率。由于提出的问题是非凸的，我们提出了一种有效的算法，它基于交替优化和连续凸优化方法来进行次优求解。计算机仿真结果表明，与基准方案相比，该算法可实现更高的最小用户速率。