## 2 System Description
### Data Collection and Transmission Unit (Drone Mapper Device)  
A system block diagram and a hardware photograph of our developed Drone Mapper device are shown in Figure 3 and Figure 4, respectively. The Drone Mapper device we developed can provide broadcast-based location information sharing between UAVs and the operators, as well as information sharing among UAVs and manned aircraft flying in the surrounding airspace, to realize safe operation for flying vehicles. This device includes the following features. First of all, the UAV communication system is based on a simple V2V broadcasting protocol without the need for network infrastructure such as a base station (BS) or access point (AP), so that it can be implemented with high flexibility. Moreover, the system uses the license-free 920 MHz band for telemetry, telecommand, and data transmission radio equipment following the Association of Radio Industries and Businesses (ARIB) standard of Japan [26]. In addition, the system can cover beyond visual line of sight (BVLOS) UAV communications with multi-hop relay communication, which contains up to two hops. Finally, the system can operate a remote information sharing system via the network by sending UAV information to UTM internet services. Regarding the detailed information of the Drone Mapper device, in Figure 3, we show the concept of designing the UAV location and ID information-sharing system. From this figure, it can be seen that there are three types of data to be collected, which are environment data obtained with sensors or a calculator, location data obtained using GNSS, and aircraft information. The three types of data are stored in the Drone Mapper's memory and can be exchanged among the helicopter, UAV, and ground monitoring station via the license-free 920 MHz band with LoRa communication. Note that the Drone Mapper device is capable of transmitting and receiving signals via a single communication antenna when it is implemented. In the current version of the Drone Mapper device, we select LoRa and FSK modulation techniques for wireless data transmission. LoRa modulation is adopted mainly because of the smaller transmission power and longer transmission distance, while its transmission  
Figure 3: Functional block diagram of Drone Mapper device. Figure 2: AFCCS with V2V communications. rate is up to max 37.5 kbps. On the contrary, FSK modulation is adopted for achieving higher transmission rates (max. 300 kbps) than the LoRa and thus improve the efficiency of data exchange. The related specifications for the developed Drone Mapper device are summarized in Table 1.  
In the considered system, the local and shared information of the UAVs is transmitted and received using wireless transmission modules. In Figure 5, we provide an illustration of the frame structure for the V2V communication protocol. To deal with interference issues, we adopt the time division multiple access (TDMA) method for the frame structure design. Specifically, we divide a frame equally into \(N\) time slots \(\tau_{1},\cdots,\tau_{N}\) and let \(\tau_{n}=\tau\ \forall n\in\{1,\cdots,N\}\). UAV\({}_{n}\) occupies the time slot \(\tau_{n}\) to transmit its local information, including position, velocity, etc. Other time slots except \(\tau_{n}\) are not used by UAV\({}_{n}\) during the flight