# ADS-B Like UTM Surveillance Using APRS Infrastructure
## 1 Introduction  
The CNS/ATM project by the International Civil Aviation Organization (ICAO) increased air traffic management (ATM) performance in the National Airspace System (NAS) by using the satellite technologies of global positioning system (GPS) and satellite communication (SATCOM) for seamless operation [1]. Under this system infrastructure and environment, the automatic dependent surveillance (ADS) was developed to enforce aircraft surveillance by broadcasting its position data to aircraft and ground ATC centers in its vicinity. ADS-B affiliates airborne aircraft for clear traffic awareness. For UAV development, the unmanned aircraft system traffic management (UTM) proposed by the National Air and Space Administration (NASA) constructs a feasible and effective system to assist UAV operation for aviation safety [2]. The UTM system is applied to small UAVs in low altitudes and to large mission UAVs into the integrated airspace. From the ATC prospective, UAVs going into integrated airspace becomes a great concern to NAS flight safety [3]. Using the same concept from ATM, a hierarchical UTM system is proposed for construction in Taiwan for civil UAVs [4]. ADS-B has been proven to be effective and efficient in aviation surveillance. It is very important both in ATM as well as in UTM. Since the traffic alert and collision avoidance system (TCAS) have become a mature standard, the active detect and avoid (DAA) mechanism enables collision avoidance from UAVs and manned aircraft to enhance aviation safety [5]. Referring to the ADS-B system concept, an ADS-B like surveillance system is proposed with four feasible systems [6]. TCAS for ATM or DAA for UTM may be executed by software to estimate the closest point of approach (CPA) between two approaching aircraft and generate warning signals for avoidance [7]. The ADS-B TCAS concept used in the air transportation system can be extended into ADS-B like DAA in the UAVs. In the developing UTM, communication downlink from air to ground is a key solution for UAV surveillance. UAV communication can use plenty of frequency resources in military systems, but it is limited in civil systems. UAVs may be classified by their weight and thrust into small or large scale UAVs with rotor wings and fixed wings. Command and control (C2) [8] is the main function for operating visual line-of-sight (VLOS) or beyond visual line of sight (BVLOS) flight. Small UAVs (sUAVs) will be legal to fly below 400 feet in urban to remote areas for a variety of applications. UAVs can be included into UTM to be transparent to ATM. For those high performance long endurance fixed wing UAVs, their operation will definitely threat NAS flights. UTM will need to merge into the integrated airspace in high altitude with ATM [2; 9]. The UTM shall link to ATM via ADS-R [10; 11]. The ADS-B like communication infrastructure is proposed by introducing 4G/LTE (long term evolution), LoRa (long range wide area network) and APRS (automatic packet reporting system) for small UAVs [6]. In UTM development [2], the airspace of 400 feet altitude is regularly controlled for small UAVs at lower speeds. In Taiwan, UAVs flying below 400 feet is authorized for local government for management, while those above 400 feet is controlled and monitored by Civil Aeronautical Administration (CAA) [4; 9]. A hierarchical UTM is constructed under such segmentation to establish regional UTM (RUTM) and national UTM (NUTM) for prompt management [4]. The proposed hierarchical UTM tries to construct a prototype for the demonstration of the UAV surveillance and collision avoidance system based on the constructed ADS-B like communication infrastructure [6]. [PERSON] et al. presented an ADS-B like system concept using 4G/LTE for the small UAV (sUAV) surveillance in low altitude [12]. Unlike manned aircraft, since sUAV are not detectable via radar or other independent surveillance techniques, the dependent surveillance mechanism shall be feasible to develop.