# High Throughput Data Relay in UAV Wireless Networks
## 2 System Model  
The role of UAVs in the context of natural disaster management is identified in Reference [25]. The main applications of systems involving UAVs are classified according to the disaster management phase, and a review of relevant research as well as the research challenges is provided in Reference [25]. In our paper, we consider a disaster scenario where a UAV is deployed within the affected area to relay the data from \(N\) ground victims to a remote information centre for coordinating search and rescue missions as the terrestrial infrastructure connecting the affected area and the information centre is damaged, as illustrated in Figure 1. The location of the \(n\)th victim is denoted by \(\mathbf{c}_{n}\in\mathbb{R}^{2\times 1}\). The UAV is dispatched to collect data from the victims for a duration of \(T\) seconds. We assume that the UAVflies at a fixed altitude of \(H\) meters and we denote its maximum speed as \(V_{\max}\) in meters/second (m/s). The initial and final locations of the UAV are assumed to be pre-determined, whose horizontal coordinates are denoted as \(\mathbf{c}_{I}\), \(\mathbf{c}_{F}\in\mathbb{R}^{2\times 1}\), respectively. We assume that \(||\mathbf{c}_{F}-\mathbf{c}_{I}||\leq V_{\max}T\) such that there exists at least one feasible trajectory for the UAV to follow. In this paper, we aim to optimize the transmission throughput from ground victims to the UAV, by jointly adjusting the wireless bandwidth scheduling and UAV trajectory. This is considered as a form of trajectory and communication resource allocation co-design problem in Reference [4]. Such problems can be first converted into more tractable forms with a finite number of optimization variables by trajectory discretization [4; 18; 20], and then utilize the more general optimization framework with Block Coordinate Descent (BCD) and Successive Convex Approximation (SCA) techniques to deal with the non-convexity [4]. Two trajectory discretization techniques, the time discretization and path discretization, are introduced in Reference [4], together with a comparison of them. Since time discretization has the advantages of equal time slot length, linear state-space representation, and the mission completion time \(T\) is assumed to be known. Therefore time discretization is considered here. For convenience, \(T\) is equally divided into \(K\) time slots, such that \(T=K\delta_{t}\), where \(\delta_{t}\) denotes the elemental slot length such that the UAV's location is considered unchanged by the ground victims during this time even at the maximum speed. Therefore, the UAV's trajectory can be approximated by the sequence \(\{\mathbf{c}[k],k\in\{1,\ldots,K,K+1\}\}\), where \(\mathbf{c}[k]\) denotes the UAV's location at time slot \(k\). To be specific, \(\mathbf{c}[1]\), \(\mathbf{c}[K+1]\) corresponds to the initial and final locations of the UAV respectively, that is, \(\mathbf{c}[1]=\mathbf{c}_{I}\), \(\mathbf{c}[K+1]=\mathbf{c}_{F}\). We compare the data transmission performance of the system when the DS method is enabled or disabled. We assume the total bandwidth of the system and the transmission power of each victim are the same. When DS is disabled, we consider two bandwidth allocation mechanisms. One is a fair allocation scheme [19]. We assume \(N\) different sub-carriers with the same bandwidth \(W\) are fairly allocated to the \(N\) victims to avoid interference during the period \(T\). The other is a bandwidth contention scheme [18; 20]. We assume the overall bandwidth \(NW\) is occupied by one victim for data transmission during each time slot. When DS is enabled, due to the limitations of transmission synchronisation and processing complexity, we assume during each time slot only transmissions from one pair of victims can be supported. In order to ensure the proper functioning of the DS method, the signal level received by the  
Figure 1: An Unmanned Aerial Vehicle (UAV)-aided wireless communication system in a disaster scenario. UAV from the supported victims are kept the same [22].