RF Source Seeking using Frequency Measurements

TL;DR

This paper presents a UAV trajectory planning method that uses Doppler frequency measurements to locate a distant RF emitter, overcoming challenges like frequency offsets, oscillator drift, and measurement noise, with proven convergence in simulations.

Contribution

The paper introduces a novel adaptive trajectory planning algorithm for UAV RF source seeking using only Doppler frequency measurements, addressing key technical challenges.

Findings

Algorithm converges to emitter vicinity in simulations

Effective handling of frequency offsets and oscillator drift

Trajectory adapts based on feedback from frequency measurements

Abstract

In this paper, we consider a problem motivated by search-and-rescue applications, where an unmanned aerial vehicle (UAV) seeks to approach the vicinity of a distant quasi-stationary radio frequency (RF) emitter surrounded by local scatterers. The UAV employs only measurements of the Doppler frequency of the received RF signal, along with its own bearing, to continuously adapt its trajectory. We propose and evaluate a trajectory planning approach that addresses technical difficulties such as the unknown carrier frequency offset between the emitter and the UAV's receiver, the frequency drifts of the local oscillators over time, the direction ambiguity in Doppler, and the noise in the observations. For the initial trajectory, the UAV estimates the direction of the emitter using a circular motion, which resolves direction ambiguity. The trajectory is then continuously adapted using feedback from frequency measurements obtained by perturbing the bearing around the current trajectory. We show that the proposed algorithm converges to the vicinity of the emitter, and illustrate its efficacy using simulations.