Article
Fixed-Wing UAV Attitude Estimation Using Single
Antenna GPS Signal Strength Measurements
Jason Gross
1,∗
, Yu Gu
1
and Matthew Rhudy
2
1
Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, WV 26506,
USA; yu.gu@mail.wvu.edu
2
Division of Engineering, Pennsylvania State University, Reading, PA 19610, USA;
matthew.rhudy@gmail.com
* Correspondence: jason.gross@mail.wvu.edu; Tel.: +1-304-293-3770
Academic Editor: Javaan Chahl
Received: 5 April 2016; Accepted: 10 May 2016; Published: 13 May 2016
Abstract:
This article considers a novel approach to using global positioning system (GPS) signal
strength readings and estimated velocity vector for estimating the attitude of a small fixed-wing
unmanned aerial vehicle (UAV). This approach has the benefit being able to estimate full position,
velocity and attitude states of a UAV using only the data from a single GPS receiver and antenna.
Two different approaches for utilizing GPS signal strength within measurement updates for UAV
attitude in a nonlinear Kalman filter are discussed and assessed using recorded UAV flight
data. Comparisons of UAV pitch and roll estimates against measurements from a high-grade
mechanical gyroscope are used to show that approximately 5
°
error with respect to both mean
and standard-deviation on both axes is achievable.
Keywords: UAV attitude estimation; GPS estimation filter; GPS signal authentication
1. Introduction
The ability to estimate an aircraft’s full position, velocity and attitude (PVA) state vector using
only a single global positioning system (GPS) antenna and receiver has several benefits. For example,
an important potential use of GPS signal strength based attitude estimation on unmanned aerial
vehicles (UAVs) is to provide an information source to warn a user if a GPS receiver is under a
spoofing attack, such as those that have been demonstrated on small UAVs [
1
]. In this context, the
ability to map GPS signal strength to attitude, or conversely, predict the expected signal strength
given an known UAV attitude (e.g., from an inertial measurement unit (IMU) ) would provide an
additional layer of information for authenticating GPS signals. That is, a GPS spoofer would not be
able to have the a priori knowledge of the UAVs attitude dynamics, and therefore would not be able
to spoof the sensitivity to GPS signal strength to receiver antenna attitude. Furthermore, for many
applications, GPS-only attitude estimates could eliminate the need for carrying and integrating an
IMU within the navigation system. That said, it is important to acknowledge that IMU systems have
become extremely lightweight and cost-effective for integration with GPS on small UAV navigation
systems [2–4].
However, the availability of GPS-only based attitude estimates double be used as an
additional information source within a fault-tolerant estimation algorithm, such as
Gu. et al. 2016 [5].
Finally, as an additional update source, when properly fused with other sensors, this could help
improve the accuracy and robustness of the overall navigation system. A single sensor that offers a
non-drifting PVA solution is attractive for many reasons.
For use in spacecraft applications, GPS signal-to-noise ratio (SNR) or signal strength readings have
been used to provide coarse attitude estimates. For example, Axerad and Behre used data from the GPS
Metrology (GPS-MET) mission to show that 3
°
–10
°
attitude estimation performance is achievable [
6
].
Aerospace 2016, 3, 14; doi:10.3390/aerospace3020014 www.mdpi.com/journal/aerospace
