## 3 Wireless Network Controllers of Drones  
There are various RF communications systems that can be used in drones. Each one of them has specific characteristics regarding frequency, transmission speed rate, range, power, and many other factors. Table 1 summarizes the main features of the RF communications systems in order to understand their usefulness and characteristics [52; 53]. Beside this, this table provides the essential data for communicating with drones, which determines which of the appropriate available RF communications system to select and use autonomously according to a predefined scenario and flight case.  
According to Table 1, the cost is significant only for satellite communications, particularly for person-viewing capabilities, but not for transmitting electronic identification. Many RF modems are already embedded in commercial drones, and the cost of adding a GPRS modem and IoT device is not a critical factor. Modern IoT devices, particularly within cities, can connect to both local smart cities IoT-deployed networks and satellites at low cost. As many commercial devices already use Bluetooth, GNSS, and GPRS RF modems for remote control, the cost factor for the majority of these devices is already included. As presented in Table 1, Bluetooth is a very good RF communication technique for low power and short distance situations, which is considered as the standard for IoT devices. Wi-Fi is the most suitable tool for high data Internet communications in applications that include a local computer, smartphone, and an IoT device network. However, Wi-Fi consumes a lot of electricity and it is limited in range, as is Bluetooth. 4G/5G is the most useful RF communications system, after the remote control, for first person viewing, remote guiding, and piloting the drones. Their usefulness comes from the fact that it has a vast network of antennas. Due to the fact that they are applied by the smartphone industry, their capabilities, bandwidth, and range are still expanding. Regarding LoRaWan IoT, as shown in Table 1, although it can achieve very long distances with very low power, it has a very low transmission rate. Thus, it cannot be used for first person view capabilities, extra-long and high data message transmission, and any other high data rate applications.  
ADS-B is not currently deployed in drones because it is a new commercial aircraft telecommunications system technology. Its initial design goal was to be more accurate than the current radar civil aviation systems, to provide accurate information about aircraft position in space, and to provide other important information to pilots, such as weather information. Some commercial drone manufacturers use it to receive information about surrounding aircraft in order to avoid collisions. ADS-B is a very useful tool for aircraft-to-aircraft communication since all aircraft will have it in the future. Satellite communications are the most suitable tool of communication for very long-range flight scenarios and especially above the sea where there are no antennas in the ground to receive information about the drones. Military drones extensively use satellite communications for first person view capabilities. Commercial drones use satellites for GPS communications and to carry small satellite modules that can send and receive very little data, suitable to give only commands.