GNSS-denied Navigation Using Direction of Arrival From Low-Cost Software Defined Radios and Signals of Opportunity
Creators: name:  A. WINTER 
name:   N. SOKOLOVA 
name:   A. MORRISON  
name:   T.A. JOHANSEN 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: UAV
FUTURE APPLICATIONS
UAV SERVICES
UAV SPECIFIC TECHNOLOGIES

description: Today, almost all outdoor Unmanned Aerial Vehicles (UAVs) rely on Global Navigation Satellite Systems (GNSS) for positioning and attitude estimation. Without aiding, the Inertial Measurement Unit (IMU) of low-cost onboard hardware will only be able to provide a reasonable state estimate for a few seconds [1]. Having an accurate and reliable state available is paramount for any autonomous operation, as the closed-loop controllers fully depend on this. GNSS provides an easy-to-use, inexpensive, global and almost entirely use-case independent solution to this problem. Virtually any outdoor mission can be flown using a sensor with a starting price lower than 20 dollars. Unfortunately, GNSS is also susceptible to deliberate or accidental interference, such as jamming and spoofing. While countermeasures in the GNSS domain, such as multiple receiver spoofing detection or beamforming exist, these usually require sophisticated and expensive receivers, and signal domain mitigation methods are less effective. The other typical approach is to allow short term GNSS outages and assume that the IMU is able to continue the flight until a GNSS solution is re-established. However, this assumption of short-term interference may not hold in many use cases, such as when using UAVs for GNSS interference localization [2]. This paper explores a novel approach using signals of opportunity for two-dimensional outdoor navigation: Similar to other established radio navigation aids such as VOR/DME, LORAN or NDBs, this method does not require user-deployed ground-based equipment, previous knowledge about the surroundings, favorable weather conditions or trackable environment features nearby, which are all typical limitations of work done by other teams on GNSS-denied navigation, for example using antenna arrays [3, 4], terrain-following radar, visual navigation, and indoor navigation technologies, respectively. The proposed localization method works by triangulation using a coherent 4-channel SDR for measuring the incoming signals angle of incidence relative to the vehicle to close-by beacons with known transmitter radio frequency and known source location. While this applies to many classes of signals, in costal areas ships and their Automatic Identification System (AIS) signals provide several favorable features, such as a widespread geometry with often multiple beacons nearby, single access to the radiocommunication channel thanks to Time Division Multiple Access (TDMA) multiplexing, high power levels (above noise floor, long-range), narrowband signals, known radio frequencies, and known source position broadcasted in the message itself. With two beacons, known heading and a barometric sensor, it is possible triangulate the current position, with three beacons it is possible to triangulate both position and heading. More than three beacons increase the quality of the solution and may provide solutions also in degenerate or singular configurations. Accuracy and precision of the calculated solution depend on the achievable measurement precision as well as the geometry (number, distance, and distribution) of the beacons and is currently under investigation. The feasibility for actual use in an airborne platform will be discussed either theoretically or based on measurement results in this paper. ========================== References [1] W. Zhao, Z. Fang and P. Li, \"Bridging GPS Outages for Fixed-wing Unmanned Aerial Vehicles,\" The Journal of Navigation, pp. 308-306, 2015. [2] N. Ahmed, A. Winter and N. Sokolova, Low Cost Collaborative Jammer Localization Using a Network of UAVs, in IEEE Aerospace Conference, Big Sky, MT, USA, 2021. [3] K. Gryte, T. H. Bryne, S. M. Albrektsen and T. A. Johansen, Field Test Results of GNSS-denied Inertial Navigation aided by Phased-array Radio Systems for UAVs, in International Conference on Unmanned Aircraft Systems (ICUAS), 2019. [4] K. Cisek, K. Gryte, T. H. Bryne and T. A. Johansen, Aided inertial navigation of small unmanned aerial vehicles using an ultra-wideband real time localization system, in IEEE Aerospace Conference, Big Sky, MT, USA, 2018.