Decentralized Multi-Agent Path Finding for UAV Traffic Management

The development of a real-world Unmanned Aircraft System (UAS) Traffic Management (UTM) system to ensure the safe integration of Unmanned Aerial Vehicles (UAVs) in low altitude airspace, has recently generated novel research challenges. A key problem is the development of Pre-Flight Conflict Detection and Resolution (CDR) methods that provide collision-free flight paths to all UAVs before their takeoff. Such problem can be represented as a Multi-Agent Path Finding (MAPF) problem. Currently, most MAPF methods assume that the UTM system is a centralized entity in charge of CDR. However, recent discussions on UTM suggest that such centralized control might not be practical or desirable. Therefore, we explore Pre-Flight CDR methods where independent UAS Service Providers (UASSPs) with their own interests, communicate with each other to resolve conflicts among their UAV operations—without centralized UTM directives. We propose a novel MAPF model that supports the decentralized resolution of conflicts, whereby different ‘agents’, here UASSPs, manage their UAV operations. We present two approaches: (1) a prioritization approach and (2) a simple yet practical pairwise negotiation approach where UASSPs agents determine an agreement to solve conflicts between their UAV operations. We evaluate the performance of our proposed approaches with simulation scenarios based on a consultancy study of predicted UAV traffic for delivery services in Sendai, Japan, 2030. We demonstrate that our negotiation approach improves the “fairness” between UASSPs, i.e. the distribution of costs between UASSPs in terms of total delays and rejected operations due to replanning is more balanced when compared to the prioritization approach.

I. Introduction

With the growing demand in commercial services provided by Unmanned Aerial Vehicles (UAVs), the conception of an Unmanned Aircraft System Traffic Management (UTM) system has become necessary [17], [18], as any ‘conflict’ [19], i.e. possibility of collision between UAVs, must be avoided. Hence, the definition of UTM regulations has generated growing interest in the development of Conflict Detection and Resolution (CDR) methods to ensure separation between UAVs. Similar to Air Traffic Management (ATM), UTM will employ three redundancy layers that are applied in different phases of a UAV’s flight [15]: Pre-Flight CDR, In-Flight CDR and Collision Avoidance. This redundancy principle is based on the guidelines of the International Civil Aviation Organization (ICAO) [13].