Quadrotor control for RF source localization and tracking

Abstract

Preliminary results on quadrotor control strate- gies enabling omnidirectional radio frequency (RF) sensing for source localization and tracking are discussed. The use of a quadrotor for source localization and tracking requires a tight coupling of the attitude control and RF sensing designs. We present a controller for tracking a ramp reference input in yaw (causing rotation of quadrotor) while maintaining a constant altitude hover or translation. The ability to track a ramp in the yaw angle is crucial for RF bearing estimation using received signal strength (RSS) measurements from a directional antenna as it avoids the need for additional gimbaling payload. This bearing or angle of arrival (AOA) estimate is then utilized by a particle filter for source localization and tracking. We report on extensive experiments that suggest that this approach is appropriate even in complex indoor environments where multipath fading effects are difficult to model. I. INTRODUCTION We investigate the problem of RF source localization and tracking using a quadrotor equipped with a directional antenna. The RF beacon could originate from a source for search and rescue in civilian/military operations or a sensor that wishes to establish an on-demandhigh data rate link. The key hurdle in solving this problem is that, in the presence of reflectors, the RF signal strength does not vary monoton- ically with distance from the source. Consequently, source localization algorithms that rely on the gradient of the RSS can get stuck in local maxima. This problem can be solved by fitting the quadrotor with a directional antenna, rotating the quadrotor repeatedly, and using the RSS measurements as the robot rotates to infer the source direction. These direction estimates can then be combined with known positions of the quadrotor in a particle filter framework to estimate the location of the RF source. We begin by mounting a directional antenna on a quadro- tor and rotating the vehicle about its vertical axis, see Figure 1. As the antenna rotates, the dominant antenna lobe picks up the signal incident from different directions, providing us with the angular RSS pattern at that point in space. We pick the direction in which the RSS is maximum as our estimate of the bearing to the source. In the presence of reflectors and noise, this estimate is prone to have significant *This work was supported by the Institute for Collaborative Biotechnolo- gies through grant W911NF-09-0001 from the U.S. Army Research Office. The content of the information does not necessarily reflect the position or the policy of the Government, and no official endorsement should be inferred.