# Resource Allocation in Unmanned Aerial Vehicle (UAV)-Assisted Wireless-Powered Internet of Things
## 3 System Model and Problem Formulation  
As shown in Figure 1, a UAV-assisted wireless-powered IoT system is proposed, which includes a power source UAV and a large number of wireless nodes [26]. The UAV is assumed to move around the wireless nodes for wireless power transfer, and the wireless nodes need harvest energy from the UAV, and use the harvested energy to transmit information. Our goal is to find the optimal resource allocation approaches for the wireless power transfer and information transmission in the proposed IoT system. In our proposed system, the wireless nodes require energy from the UAV, and transmit information to the UAV using the received energy. The UAV works as the power source that moves around to charge the wireless nodes. The UAV can also gather all the information from the wireless nodes. In this paper, although the wireless nodes are randomly distributed in the IoT environment, they are all assumed to be charged by the UAV. In the IoT system, different wireless nodes will be allocated different tasks for data collection and transmission, and the energy consumptions of the wireless nodes should be different. Based on this assumption, in order to distinguish the various wireless nodes, we divide the wireless nodes into two categories. One includes the higher energy consumption nodes (HEC nodes), which need more energy for data collection and transmission, and the other includes the lower energy consumption nodes (LEC nodes), with lower energy requirements. Then, the energy transferred to the wireless nodes from the UAV will be different. The HEC nodes may have more energy transferred from the UAV compared with the LEC nodes. During the data transmission, the wireless nodes in the same energy consumption category are assumed to share the same channel, and will cause inter-channel interferences. It is assumed that when the UAV transfers energy to the wireless nodes in one category, there is no energy transfer and information transmission between the UAV and the wireless nodes in the other category. Then, the intra-channel interferences between the two categories can be ignored. The aim of the paper is to find the optimal resource allocation solutions for the UAVs to harvest the wireless nodes, and for the wireless nodes to transmit information. It is assumed there are \(N_{H}\) nodes in the HEC category,  
Figure 1: System model. UAV, unmanned aerial vehicle. and N\({}_{H}=[1_{H},\ldots,N_{H}]\) is the HEC nodes set. The number of the nodes in the LEC category is denoted by \(N_{L}\), and the LEC nodes set is N\({}_{L}=[1_{L},\ldots,N_{L}]\). Because the wireless nodes use the harvested energy for information transmission, the wireless nodes should pay for the UAV for energy harvesting and the resources for information transmission are affected by the available harvested energy. UAV can control the power level for energy transfer and can control the unit energy price for the wireless nodes. Based on all these assumptions given in the above, the UAV is considered to be the leader of the dynamic game, and the wireless nodes are treated as the followers. The relationships between the UAV and the wireless nodes are shown in Figure 2.  
Let \(p_{H,i}(t)(i\in\{_{H}\})\) denote the allocated resource of the HEC nodes, and \(p_{L,i}(t)(i\in\{_{L}\})\) represent the allocated resource of node \(i\) in the LEC category. In order to achieve information transmission between the wireless nodes and the UAV, the allocated resources given by \(p_{H,i}(t)(i\in\{_{H}\})\) and \(p_{L,i}(t)(i\in\{_{L}\})\) mean the minimum energy requirements of the wireless nodes from the UAV. The wireless nodes transmit information to the UAV using the required energy from the UAV. When the wireless nodes obtain the energy form the UAV, they can use the obtained energy to transmit the information and earn revenue from the information transmission process. As the wireless nodes in the same category transmit information in the same channel, there exists inter-cell interference among the wireless nodes in the same category.