A Universal Traffic Management System for Unmanned Aerial Systems With Or Without Automatic Dependent Surveillance-
Broadcast
Ting Huong Yong1*, Sim Yee Wai2, Tay Yen Pei3, Elton Wong Kee Sheng1
1 Drone Research and Application Centre, University College of Technology Sarawak, Sibu 96000, Sarawak, Malaysia
2 Quest International University Perak, Ipoh 30250, Perak, Malaysia
3 Smart Connectivity Lab, Simplify Networks, Kuala Lumpur 50000, Malaysia
*Corresponding Author: [email protected]
Accepted: 15 February 2021 | Published: 1 March 2021
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Abstract: The meteoric rise of commercial Unmanned Aerial System (UAS) usage in various industries such as agriculture, construction and delivery services, accelerated the need for an integrated air traffic management system to improve control and safety. This paper identifies the limitations with existing surveillance systems for UAV tracking and proposes a Universal Traffic Management (UTM) system aiming to monitor both commercial aircraft and Unmanned Aerial Vehicle (UAV) flight traffic with and without Automatic Dependent Surveillance-Broadcast (ADS-B) technologies. The system also aims to create a federated open system architecture that is compatible and interoperable with existing UAS, surveillance technologies and air safety regulations endorsed by International Civil Aviation Organization.
Furthermore, the paper presents the findings from its prototype deployment with respect to its feasibility, compatibility and performance, and leads to defining a set of UAS traffic management guidelines required to work in conjunction with such a system.
Keywords: Air Traffic Safety, Automatic Dependent Surveillance-Broadcast, Drone, Traffic Management, Unmanned Aerial System
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1. Introduction
The Federal Aviation Authority (FAA) estimated that more than 2.3 million new unmanned aerial systems (UAS) would fill the national skies by the end of 2024 (Federal Aviation Administration, 2020). Coupling with the rapid rising number of commercial UAS usage worldwide, the establishment of a traffic management system for UAS becomes highly essential, for the safety, efficient capacity allocation on the use of airspace and air traffic control. This paper identifies various limitations of existing surveillance systems to accommodate UAV tracking in the aspects of range, accuracy and latency. The lack of effective UAS regulations and operating guidelines have put a limit to mass commercial drone usage (Jones, 2017) in agriculture (Tripicchio et al., 2015), construction (Siebert and Teizer, 2014), delivery services (Goodchild and Toy, 2018), etc.
This research work proposes a universal system architecture for UAS traffic management with and without automatic dependent surveillance-broadcast (ADS-B). An evaluation on a Universal Traffic Management (UTM) system developed in this research is also discussed based on the findings gathered in the actual deployment of the system. The Automatic
time identification, information exchange and collision avoidance manoeuvre as part of a UAS traffic management system.
Furthermore, we reckon that the effectiveness of any new system would not be complete without the introduction of new policies and processes. This leads to defining a new set of UAS traffic management operating guidelines covering pre-flight, on-flight and post-flight scenarios.
The outcome of this paper shall provide aviation authorities a system roadmap and a framework to guide building and implementing a universal UTM system for both commercial aircraft and UAVs to operate safely in a beyond visual line of sight (BVLOS), segregated aviation traffic scenarios (Federal Aviation Administration, 2020) which shall enable broader applications of commercial UAVs in various industries.
2. Problems with the Existing Surveillance Systems
Most UAVs are generally small, lightweight, autonomous and agile. Tracking and managing UAV traffic requires special policies, processes and platforms. Although aviation regulation agencies have introduced safety guidelines and restrictions on UAV’s usage (UAV Coach, 2020), the current measures are neither sufficient for safety enforcement nor cost-effective e.g.
violation monitoring, trespassing into restricted airspace, accidents prevention and high surveillance cost.
Notably, we have identified three major shortcomings in the contemporary systems employed in managing the air traffic for manned commercial and military aircraft. Firstly, the current surveillance systems e.g., primary, secondary surveillance radars, are not capable of detecting, identifying and communicating with UAVs effectively. The inherent inaccuracy and long latencies of these radar systems make it impractical for ensuring a safe spacing between UAVs and other commercial aircraft. Special purpose-built UAV tracking radars are expensive to deploy with short detection range (Guvenc et al., 2017) while acoustic-based (Haddad et al., 2019) and computer vision drone detection (Pham and Nguyen, 2020) technologies are largely immature. At the present state, ADS-B is being enforced only for commercial aircraft and in some countries, ADS-B is only required for specific airspace e.g., non-radar airspace. In addition, most commercial UAVs do not come with ADS-B apparatus built-in.
Secondly, regulations in most countries have been enforced such that it is made compulsory to register commercial UAS (comprising of both the UAVs and the pilots), permitted to fly in unrestricted airspace capped below 120m (or 400 feet) above ground level, within line-of-sight of the pilot (Kopardekar, 2014). These guidelines cannot be effectively enforced at the absence of a real-time UAS flight traffic tracking. In addition, regulatory enforcement of low-altitude unmanned flights is delegated to local authorities, by the state or city enforcement agencies (Foina et al., 2015) and hierarchical UAS traffic management (Lin and Shao, 2020) creates layers of bureaucracy that could undermine the rapid disaster management.
Neither the airspace classifications (unrestricted and/or Class A, B, C and G restricted airspace) are published on public domains, nor there is a direct or real-time communication channel between the drone operators, manned aircraft pilots as well as air traffic controls (ATC) in times of emergency. Such system limitations expose unprecedented threats (Lacher et al., 2019) to our public safety (Clarke and Moses, 2014) and reduce the limitless potentials of large scale
commercial UAS operations. Hence, these problems lead to an opportunity to define, develop and deploy a more open, federated and sustainable system for UAS traffic management.
3. Universal Unmanned Aerial System Traffic Management System
In this section, we propose to develop a UTM system, which serves as a single centralized cloud-based solution for tracking both commercial aircraft and UAV flight activities at real- time. The system architecture details the required and optional system components based on various flight scenarios, regulatory requirements and deployment configurations specified hereafter.
Real-time UAV Tracking with ADS-B
ADS-B technology has been a de facto standard adopted by most major aviation authorities and industry players. Both the United States’ Federal Aviation Authority (FAA), European Union’s Aviation Safety Agency (EASA) and Australia’s Civil Aviation Safety Authority had issued mandates to all commercial airlines and flight operators to equip their aircraft with ADS- B apparatus. Other countries are expected to follow as they need to comply under the International Civil Aviation Organization (ICAO) Global Air Navigation Plan (GANP) initiative.
In the first UTM system architecture (see Figure 1), the authors proposed equipping each commercial UAV with an ADS-B transceiver. An UTM system prototype was developed to further examine its deployment feasibility in terms of time, cost and effort, as well as its compatibility with other existing air traffic surveillance systems, commercial ADS-B transceivers and UAVs. In the deployment, we fitted uAvionix’s ping2020i ADS-B transceiver to a DJI Matrice 200 drone, capable of broadcasting real-time flight location, altitude, trajectory and other flight information to nearby aircraft and ADS-B ground stations. ADS-B broadcast messages can be picked up by FlightRadar24’s ADS-B Mode S receiver (Flightradar24, 2020) installed on the ground and relayed to the UTM’s flight database hosted on the cloud. UAV’s flight path and real-time positions are plotted on a map displayed on the UTM dashboard, with data refreshed at one-second interval.
ADS-B provides a positional accuracy within 0.05 nautical miles (nm) with an integrity limit of less than 0.2nm. ADS-B error in transmission can be minimized (Lin et al., 2020), corrected (Ali et al., 2014) and improved using prediction models (Cho, 2017). In our test, the ADS-B receiver is capable of receiving broadcast messages from aircraft as far as 218nm away, at 2 messages per second with 98.9% availability (see Figure 2). Data transmission latency between the ADS-B receiver site and the UTM’s cloud database can be improved using fibre Internet.
Aircraft detection range can be further expanded across a region with multiple ADS-B receivers installed at non-overlapping locations. For instance, the entire Sarawak airspace can be effectively covered by hosting at least 3 ADS-B sites, with the first being deployed in Sibu (see Figure 3) as part of this research work.
Figure 1: The system architecture of UTM System with ADS-B
Figure 2: Flight detection and tracking on FlightRadar24’s ADS-B Receiver Dashboard
Figure 3: The effective surveillance area proposed to cover the entire Sarawak airspace with at least three ADS-B sites positioned at Kuching, Sibu and Miri respectively
Real-time UAV Tracking without ADS-B
Since deploying and enforcing ADS-B systems can be expensive, this research also developed a second UTM system architecture that caters for countries or regions that may already have radar-based surveillance systems e.g., Primary Surveillance Radar (PSR) or Secondary Surveillance Radar (SSR), or are in the midst of making transition to ADS-B. In this variant, near real-time UAV tracking can still be achieved without ADS-B system.
In this deployment, the same DJI Matrice 200 drone was used but without an ADS-B transceiver. The authors have further developed a custom UTM mobile application, installed on the UAV pilot’s smartphone which is attached to a DJI GL900A remote controller (see Figure 4). As a pre-requisite, the pilot’s smartphone must have ubiquitous Internet access at flight time. During the flight, real-time data such as altitude, position, velocity, battery level and motor status etc. are transmitted directly from the UAV to the UTM mobile application and subsequently relayed to the flight database hosted on the cloud.
Based on our test, the UAV positional accuracy is within 5cm, with average transmission latency of 1.2 second. The UAV detection range is not limited by the surveillance system coverage as long as the UAV is within the pilot controller’s range, typically within 5 miles. In addition, the UAV waypoint mission can be retrieved by the UTM upfront, giving air traffic control an advanced insight into UAV planned flight routes. Nevertheless, this deployment architecture only caters for DJI-based drones, which comprise to about 70% of worldwide commercial drone market. In the future, the UTM mobile application can be further expanded to support other popular UAV platforms e.g., Pixhawk. In order to detect and track commercial aircraft in the UTM, integration with other existing surveillance systems is required.
Figure 4: The system architecture of UTM System without ADS-B
4. Guidelines for UTM System Implementation
Successful adoption and implementation of UTM requires a set of comprehensive operational guidelines covering pre-flight, on-flight and post-flight measures, coupling with real-time UAV surveillance, communications and mitigation capabilities. This section highlights the key operational requirements and guidelines for each of the stages above, which are essential in attaining beyond line-of-sight capability as well as autonomous surveillance and collision avoidance.
Pre-Flight Guidelines
The guidelines recommend that authorities who are implementing UTM system to make it mandatory for all commercial UAS to be registered, equipped and certified with ADS-B Out transceiver. Registered UAS shall receive an official call sign. Further to that, all commercial UAS operators must apply for flight permit to operate UAV flights below 120m above ground level.
Applications of flight permit can be made by licensed pilots through a centralized UTM Flight Authorization System by detailing its flight paths on controlled airspace. Collision avoidance can be ensured using conflict detection logic (Cauwels, 2020) integrated to the UTM. All permit requests shall be checked against the UAS registration database, licensed pilot database, airspace data sources, such as Facility Maps, Special Use Airspace data, Airports and Airspace Classes, as well as temporary flight restrictions and notices to airmen. If approved, UAV pilots will receive an authorization to fly permit with a unique flight identification number.
In-Flight Guidelines
During the flight, ADS-B out transceiver has to be enabled, set with the given flight identification number and remain functional at all times with all flight data logged. UAV flying without a permit in controlled airspace or deviating from its permitted flight path or approved zone shall be prosecuted. The deployment of separate counter-UAS system at airports or
intrusion, is highly essential. UAS mitigation or countermeasures need to include the capability to disrupt, disable, destroy, take control of, and/or provide alternate flight instructions to an UAV.
Post-Flight Guidelines
Since UTM flight database contains real-time flight data, the system may further be equipped with the capability to conduct cross-validation of planned flight path against the actual flight route. Periodical physical audit must be carried out by the authority to check the validity of the registered UAV, certified pilot license, airworthiness of the ADS-B apparatus, permits and other flight details.
5. Conclusions
The rapid evolution of UAV technologies and the lack of policies have given rise to numerous restrictions on UAV applications at a massive scale. Inclusion of UAS surveillance into existing air traffic control systems can be challenging, without the introduction of new policies, processes and platforms. The UTM system and guidelines proposed in this paper offer future- ready compatibility with ADS-B standard, rapid deployment, high performance and flexible integration with existing surveillance systems. Authorities and regulatory agencies may adopt a phased approach in providing low-altitude beyond visual line of sight (BVLOS) traffic management for UAS in controlled airspace, starting with a non-ADS-B architecture to ADS- B architecture, with the ultimate goals to facilitate airborne traffic situational awareness, spacing, separation and self-separation mechanisms for commercial aircraft and UAVs.
Acknowledgement
This research work was funded in part by the Sarawak Multimedia Authority under Sarawak Digital Economy Grant #2019/18006.
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