UAV Landing at an Unknown Location Marked by a Radio Beacon

We consider the problem of minimizing the time to approach and land near a target radio beacon at an unknown location with an Unmanned Aerial Vehicle (UAV). We show that a cone-like region exists above the target inside of which bearing measurements of a directional antenna lose directionality: signal recordings in all directions yield similar signal strength. We present a geometric model of this region based on antenna simulations and data collected with a real system. Our main contribution is a strategy that takes advantage of a UAV's ability to change altitude and exploits a special structure occurring when approaching the target beacon from above to reduce the flight time required to land near the beacon. We analyze the performance of our strategy and demonstrate through simulations that by exploiting this structure we can achieve shorter flight times than our previous work.

I. Introduction

Landing near the source of radio signal (beacons) with Unmanned Aerial Vehicles (UAVs) has many important applications. In search and rescue applications, beacons can mark the location of an emergency package delivery like rations and medicine [1], defibrillators [2] and flotation devices [3]. In environmental monitoring applications, radio-tagging animals can be used to mark their location [4], [5] and can be a useful wildlife and farm management tool. UAVs equipped with a directional antenna that can track radio beacons are a good fit in such scenarios due to their ability to travel fast, reach difficult to access areas and carry small payloads.