On Cooperative Achievable Rates of UAV Assisted Cellular Networks

In this paper, we study an UAV base station (UBS) assisted cellular network that consists of a single ground macro base station (MBS), multiple UBSs, and multiple ground terminals. We assume that the MBS transmits to the UBSs and the terminals in the licensed band while the UBSs use a separate unlicensed band (e.g., Wi-Fi) to transmit to the terminals. For the utilization of the UBSs, we propose a cooperative decode-forward (DF) protocol in which multiple UBSs assist the terminals simultaneously while maintaining a predetermined interference level on the coexisting unlicensed band users. For our network setup, we formulate a joint optimization problem for minimizing the aggregate gap between the target rates and the throughputs of terminals by optimizing over the 3D positions of the UBSs and the resources (power, time, bandwidth) of the network. To solve the optimization problem, we propose an efficient nested structured algorithm based on particle swarm optimization and convex optimization methods. Extensive numerical evaluations of the proposed algorithm is performed considering various aspects to demonstrate the performance of our algorithm and the gain for utilizing UBSs.

I. Introduction

Utilizing unmanned aerial vehicles (UAV) as mobile base stations (BSs) is a new paradigm that can enhance network throughput and extend coverage [1]–[3] in cellular networks. Unlike static ground base stations, UAV base stations (UBSs) can be dynamically deployed by adjusting their positions to support various quality of service (QoS) requirements and balance load between heterogeneous cells in a timely fashion [4]. In some cases, for instance, natural disasters or in marine environments, deploying ground BSs in a timely manner can be almost impossible, and for such cases a UBS aided communication network may be a critical option [5]. As discussed in these use cases, the main advantage for using UAVs as aerial BSs comes from their mobility and promptness, which provide an efficient way of establishing alternative wireless links. In order to fully utilize such wireless links, however, the positions of the UBSs have to be carefully optimized while considering the data traffic demands, or more generally, the overall QoS requirements of the heterogeneous users and services.