A Multi-Antenna Vector Tracking Beamsteering GPS Receiver for Robust Positioning
Type of DegreeMaster's Thesis
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This thesis proposes the coupling of a Global Positioning System (GPS) L1 C/A vector tracking software-defined receiver with controlled reception pattern array array (CRPA) satellite constrained beamsteering, i.e. a multi-antenna high-gain vector tracking receiver. As technology advances, the number of systems relying on Global Navigation Satellite Systems' (GNSS) precise positioning and timing is increasing. Improvements in robustness and overall design are necessary for receivers to estimate position, velocity, and time accurately in all environments. This work is inspired by previous receiver designs by NAVSYS and the German Aerospace Center (DLR). The proposed receiver conducts pre-correlator beamsteering. Pre-correlator beamsteering is lower SWaP-C as it reduces the number of receiver correlator channels compared to DLR's post-correlator implementation. The vector tracking receiver feeds back attitude corrected satellite geometry to a beamsteering module that updates the beam constraints as vector tracking's extended Kalman filter (EKF) applies corrections. The proposed receiver is compared to a multi-antenna scalar tracking receiver in all testing scenarios. Comparisons are also made with a single-antenna vector tracking receiver, a single-antenna scalar tracking receiver, and a commercial-off-the-shelf (COTS) receiver. In simulation, receiver performance using a range from one to eight element CRPAs is compared to understand the benefits different arrays offer to receiver design. The simulations show there is a diminishing return in signal quality improvements as the number of elements increase. The simulations also show that a seven and eight element implemented vector tracking receiver can track signals at carrier-to-noise ratios as low as 12 dB-Hz, which is much lower than previously documented tracking thresholds. The proposed receiver outperforms the other receivers when the simulation scenarios are noisy, improving PVT estimates considerably. Four element configurations of the receivers are tested with dynamic live sky collected data. The multi-antenna high-gain vector tracking receiver outperforms the other receiver designs, aligning closely with the COTS receiver. The multi-antenna high-gain vector tracking receiver’s performance is followed by the single-antenna vector tracking receiver, the multi-antenna scalar tracking receiver, and the single-antenna scalar tracking receiver, respectively. The receivers are also tested in a jamming environment. The proposed receiver offers a four dB improvement in jamming resilience compared to the single-antenna vector tracking receiver.