This paper considers an unmanned aerial vehicle (UAV) base station (BS) network with delay-sensitive users and delay-tolerant users on the ground, which have different quality-of-service (QoS) requirements. In the network, the backhaul link connecting the backhaul gateway and the UAV-BS shares the same spectrum with the data links connecting the UAV-BS and the users due to spectrum scarcity. To improve the rate performance of the delay-tolerant users and to guarantee the QoS of the delay-sensitive users, we aim to maximize the minimum rate of the delay-tolerant users by jointly optimizing the bandwidths of the backhaul link and the data links, the transmit power allocated to different users and the trajectory of the UAV-BS, subject to the constraints on UAV mobility, total bandwidth, total transmit power, backhaul data rate, and minimum rate requirements of the delay-sensitive users. Although the formulated problem is non-convex and difficult to solve optimally, we propose an efficient algorithm to find a suboptimal solution to it. Simulation results show that the proposed joint optimization algorithm achieves significantly higher minimum user rate than the benchmark schemes.INDEX TERMS UAV base station, bandwidth and power allocation, trajectory optimization, backhaul constraint, quality-of-service.

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