# High Throughput Data Relay in UAV Wireless Networks
## 1 Introduction  
Due to the advantages of high mobility and reduced cost, Unmanned Aerial Vehicles (UAVs) have found promising applications in wireless communication systems [1; 2], not only to support the existing cellular networks in high-demand and overload situations, but also to provide wireless connectivity in scenarios lacking infrastructure such as battlefields or disaster zones. Compared with terrestrial communications, UAV-aided wireless systems are in general faster to deploy [3], more flexible to reconfigure, and likely to have better communication channels as a results of Line-of-Sight (LoS) links. The 5G cellular network is expected to support a peak data rate of 10 Gb/s with only 1 ms round-trip latency, which is adequate for UAV communication applications [4]. Integrating UAVs into a cellular network is regarded as a new paradigm [4]. The role that a UAV performs in a wireless communication system typically follows either of two types--firstly, the UAV can be deployed as an aerial Base Station (BS) for the ground terminals [5]; secondly, the UAV can be deployed as a mobile relay providing wireless connectivity between distant ground terminals [6; 7; 8]. The relay often plays an important role in wireless communications [9; 10; 11]. How to deploy a UAV in a wireless communication system is a popular research topic [12; 13], as it is related to energy consumption and data transmission performance. There are primarily two categories of UAV deployment study, static deployment of the UAV [14; 15; 16] and the use of mobile UAVs [17; 18; 19; 20]. The efficient deployment of a UAV acting as a wireless BS providing coverage forground terminals is analysed in References [14; 15]. In Reference [16], the authors propose an intelligent strategy that allows UAVs to perform tactical movements in a disaster scenario, combining the Jaccard distance and artificial algorithms for maximizing the number of served victims. However, the analysis is based on static deployment of the UAV. The authors of Reference [21] propose a simple but effective dynamic trajectory control algorithm for UAVs. The proposal adjusts the centre coordinates and the radius of UAVs' trajectories in order to alleviate congestion. Nevertheless, the method is implemented by a UAV control station, which introduces control signal overhead. In regard to mobile UAV deployment, the UAV flight trajectory is planned considering the wireless communication features. A UAV that acts as a mobile BS serving a group of ground terminals to maximize the throughput is demonstrated in Reference [17]. The UAV flies in a cyclical pattern and the ground terminals are located along a straight line, rather than a 2D plane. An energy-efficient data collection problem in UAV-aided wireless sensor network is solved in Reference [18]. The authors only consider one common transmission channel that all the sensors have to contend for using a time division multiple access scheme. The resource allocation and trajectory design for energy-efficient secure UAV communication system is studied in Reference [19]. The authors consider the ground terminals to transmit data via separate sub-carriers so as to avoid interference. A joint trajectory and communication design for UAV-enabled system is elaborated in Reference [20]. The data transmission in these above-mentioned works are in orthogonal channels, either in different time slots or in different transmission bands. However, bandwidth efficient techniques which allow different data signals to be transmitted during the same time slot and radio band have not been considered in the UAV-aided wireless communication systems. In this paper, in order to improve the throughput of the system, a bandwidth efficient technique named the Dual Sampling (DS) method [22] is employed in the data transmission procedure. In Reference [23] DS is applied in stationary caching network to enhance the throughput. This time, we focus on the usage of DS method in a mobile UAV network.