## 1 Introduction
### Related Surveys  
The study provided in this paper is unique in many aspects and thus differs from the existing review articles on UAV-based wireless communication applications. For instance, a conference paper [10] focused on distributed processing applications for UAVs, while [11] reviewed 3D wireless ad hoc and sensor networks. The authors in [12] surveyed the use of multiple UAVs for persistent surveillance and [13] studied the use of UAVs for civil applications. On a similar note, UAV applications for civil infrastructure are surveyed in [14]. The authors of [15; 16; 17] focused on UAV-assisted disaster management and [18]  
Figure 1: Illustration of UAVs deployed in different applications. reviewed UAV-based intelligent transport for smart cities, while [19] studied UAV swarm and nanosat applications and architectures. The collaborative deployment of UAVs and WSNs for monitoring is reviewed in [20], while autonomous inspection via multi-UAV is studied in [21] and UAV applications in WSNs are reviewed in [22]. The authors in [23] surveyed green UAVs for public safety applications, while [PERSON] et al. [24] reviewed the deployment of aerial wireless relays for emergencies. Generally, FANET technologies and applications have been studied in [25]. Key issues related to UAV data collection in the IoT were reviewed by [PERSON] et al. [26], while UAV applications for precision agriculture were surveyed in [27]. The authors in [28] focused on viticulture, while UAV-based air quality monitoring was discussed in [29]. In [30], the authors reviewed mobile edge computing in UAV networks, while [31] studied air-ground integrated edge systems. For future wireless technologies, ref. [32] studied UAV softwarization applications and trends, while the use of UAVs for 5G and beyond was surveyed in [33]. Finally, the Internet of Flying Things (IoFT) was reviewed in [34]. Apart from the aforementioned, several other surveys have been published on UAVs (see Table 1). None of these studies thoroughly investigated the fundamental technical considerations in the subject of AoI minimization in UAV-assisted data gathering in WSN and IoT applications. In relation to AoI-related studies, surveys on AoI have recently appeared in the literature with diverse focus areas. For instance, the concept of AoI and its optimization in wireless communication networks, in general, are discussed in [35] with some discussion on definitions, variants, sampling policies, packet management strategies, resource-constrained source nodes involving EH, and UAV-assisted sampling. The authors of [36] mainly focus on AoI in Ambient Intelligence (AmI) IoT networks, methods, metrics, and their queuing and scheduling policies. The authors in [37] focused on methods, metrics, and AoI optimization in low-latency cyber-physical systems and applications requiring timely status updates. In contrast to all the aforementioned surveys, this paper studies the literature on UAV-assisted data gathering in WSN/IoT applications with the goal of identifying the most fundamental design considerations/aspects, classifying them based on how they have been jointly considered, identifying critiques of some of these works based on the literature, and highlighting some of the challenges and future considerations in this area. Table 2 summarizes surveys related to AoI minimization in UAV-assisted data gathering. On the contrary, the main focus of this paper is not on methods, algorithms, and assumptions related to this research field. Rather, this paper is meant to be an introductory survey for those planning to construct a similar network architecture or hypothesize the network performance, keeping in view different design considerations. It is worth noting, however, that we have also conducted a comprehensive study focusing on metrics, methods, assumptions, and other influencing factors on AoI minimization for UAV-assisted data gathering in WSN/IoT networks (refer to [38]).