UAV-Aided Network Localization Using Radio Phase Measurements

This paper considers the problem of ground users localization aided by an unmanned aerial vehicle (UAV) flying radio capable of collecting measurements from users. To do so, we exploit the phase information of the received radio signals from users at the UAV in different locations along with time-of-arrival (ToA) measurements. The location of the UAV is also not perfectly known, hence the problem at hand turns to a simultaneous user localization and tracking of the UAV location. The phase measurements are inherently more precise than ToA measurements while bringing ambiguity since it follows a periodic behavior. To solve this issue, we unwrap the phase measurements by tracking the phase while the UAV moves. Then a time-difference-of-arrival (TDoA)-based algorithm is proposed by treating each UAV location as a virtual antenna/anchor (yet with unknown locations) and exploiting the unwrapped phase measurements to precisely localize the users and jointly track the UAV trajectory. We employed a least-squares simultaneous localization and mapping (SLAM) framework to fuse TDoA data, estimated from phase, with other measurements such as ToA, an erroneous estimate of UAV location available from GPS, and the UAV velocity measured by an inertial measurement unit (IMU) onboard. The simulations verified the performance of the developed algorithm when compared to other benchmarks including scenarios with traditional terrestrial anchor-enabled localization systems.