## 1 Introduction  
Non-terrestrial networks (NTN) are an effective solution that can provide wireless communication services over uncovered or under-served areas towards Beyond 5G [1]. NTNs are a communication platform for connecting devices in various locations ranging from the sky to seas and space, through different vehicles such as satellites, aircraft, and ships. In particular, when unmanned aerial vehicles (UAVs), also known as drones, are employed as flying wireless base stations, it becomes possible to construct wireless networks in the air, and various relevant research has been reported in this research area [2]. In recent years, the development and applications of UAVs has shown rapid growth. Because the UAVs have very outstanding mobility that is not limited by all kinds of terrain, they can provide high convenience and good accessibility in scenarios such as package delivery in isolated areas or disaster investigation [3, 4]. As a result, many new wireless technologies, such as Internet of Things (IoT), can be improved or extended using UAVs. However, as the development of UAVs is highly growing, the safety of UAV operations becomes an emerging issue worldwide. For safe UAV operation issues, it is essential to develop a suitable and effective UAV control system, also called an unmanned aircraft system (UAS) [5; 6; 7; 8]. However, for multiple UAV scenarios, awareness of neighboring flying vehicles while keeping a safe enough distance among flying objects is a very tough task. Especially for UAV applications nowadays, the flying distances for UAVs are usually very long and it is almost impossible to confirm the flying circumstance with human eyes, which makes a great threat to the UAV flight safety operation issues. Hence, a mechanism to automatically perform UAV awareness and information sharing is very important for modern UAS applications. In traditional approaches, UAS relies on existing commercial communication networks, such as cellular or satellite networks, to enable the implementation of UAS traffic management (UTM) functions for UAVs [9; 10; 11; 12]. However, in critical UAV scenarios, such as large-scale disasters, it is common for the communication network infrastructure to be damaged or disabled, which makes UTM ineffective. As a result, UAVs are forced to operate in high-risk conditions, so that their safety and effectiveness are hardly guaranteed. Considering that existing cellular networks are suitable only for terrestrial communication and have limitations in supporting aerial communications, the authors of [13] presented a future perspective on 6G-enabled UTM ecosystems, with a focus on non-terrestrial features, including aerial and satellite communication. Similarly, the authors of [14] identified the most promising 6G enablers for UAV communication and examined the peculiarities of direct device-to-device (D2D) communications in the sky. More recently, to address collision issues, [15] evaluated a reduction in separation distances between UAVs using Wi-Fi- and Bluetooth-aided communication techniques through simulations. The topic of integrated systems based on wireless sensor networks and UAVs has also sparked extensive discussion in [16]. In [17], D2D communications extended to UAV systems are considered important concepts for the future. In [18; 19], the authors reveal the potential applications of UAV-assisted communications with AI technologies in 5G/6G systems. Undoubtedly, the most significant challenge at present is how to achieve UAV communication without any infrastructure support. Given the aforementioned descriptions, addressing the sharing of UAV locations within the neighborhood airspace without cellular or other existing networks becomes crucial for ensuring UAV safety. In our study, this can be achieved through the implementation of vehicle-to-vehicle (V2V) communications, enabling UAVs to share their locations with each other as well as with the ground operation station.