###### Abstract  
Although Unmanned Aerial Vehicles (UAVs)-aided wireless sensor networks (WSNs) have gained many applications, it is not for long that research works have been produced to define effective algorithms and protocols. In this article, we address the UAV-enabled WSN (U-WSN), explore the performance and the capability of the UAV, define the UAV functionalities as a communication node, and describe the architectures and the relevant typical technologies that emerge from this new paradigm. Furthermore, this article also identifies the main factors which influence the U-WSN design and analyzes the open issues and challenges in U-WSN. These insights may serve as motivations and guidelines for future designs of UAV-enabled WSNs.  
wireless sensor networks; unmanned aerial vehicles; non-terrestrial networks; network architecture; mobility; trajectory planning +
Footnote †: journal: Journal of Applied Physics  
0000-0001-9993-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-3300-  
make them under control. The ground platform could be composed of many sensor nodes, base stations, and data center according to applications. In applications, e.g., UAVs are dispatched for aerial photography, no ground sensors needed to be deployed. Thus, the ground sensors are not mandatory in a U-WSN.  
The design of U-WSN applications requires wireless networking techniques. Although many protocols and algorithms have been proposed for traditional WSN applications, they can no longer meet up with the unique features and application requirements of U-WSN. The main differences between WSN and U-WSN are outlined below:  
* The topology of a U-WSN changes more frequently.
* The sensors are prone of being out of the range of the UAV if they have high relative velocities.
* The scale of the area of a U-WSN can be several orders of magnitude higher than the scale of a WSN.
* The UAVs are very limited in power compared to the ground sensor nodes and the base station.
* The UAVs need to be dispatched to maintain a safe flight and other issues.  
Many researchers are currently engaged in developing schemes that fulfill these requirements. This paper presents a review of UAV-centric architectures, applications, and open issues. We aim better to understand the current research issues in this field. We also attempt to investigate design constraints and outline specific tools to meet the design objectives.  
The main contributions of this paper are summarized as follows:  
* analyze the performance and the capabilities of the UAV, based on which, we summarize the U-WSN applications.
* refine the UAV functionalities as a communication node in a U-WSN.
* compare and draw the network architecture and the standard technologies in U-WSN.
* evaluate the main factors which influence the U-WSN design.
* review and analyze the open issues and challenges in U-WSN.  
The organization of this article is as follows: In Section 2, summarize the performance and capability of the UAV, and the relative applications of the U-WSN, and the functionalities of the UAV as a communication node. Section 3 analyzes the factors that influence the U-WSN design. Section 4 presents open issues and challenges in U-WSN. Section 5 gives a conclusive remarks of this work. Finally, Section 6 concludes this work.