Vector Tracking of GNSS Signals from a Multi-Element Antenna

Michael C. Esswein and Mark L. Psiaki

Abstract:	A new vector loop has been developed to track code phase, beat carrier phase, carrier Doppler shift, amplitude, polarization, and Direction of Arrival (DoA) using GNSS signals from a small multi-element antenna array. Each antenna will have two feeds, one primarily sensitive to Right-Hand Circularly Polarized (RHCP) signals and one sensitive to Left-Hand Circularly Polarized (LHCP) signals. The antenna system and vector tracking loop have been designed to be part of a system that ensures resilient Position, Navigation, and Timing (PNT) in the presence of GNSS jammers and spoofers. The tracking loop uses an Extended Kalman Filter (EKF) implemented in Square Root Information Filter (SRIF) form. The Kalman filter is augmented to provide Delay Lock Loop (DLL) and Phase Lock Loop (PLL) feedback estimates for the receiver to use in its standard code and carrier mixing operations. Measurement input data to the Kalman filter takes the form of early, prompt, and late In-Phase and Quadrature accumulations. Tracking occurs downstream of a blind null steering algorithm and after signal acquisition. The Kalman filter’s model of the accumulation measurements is specially tailored to include the distortion effects of the upstream blind null steering operations. A Multiple Model Filter (MMF) is used, as needed, to account for large uncertainties in initial DoA estimates from a fine acquisition calculation. The performance of the Kalman filter tracking loop is analyzed using simulations in which multiple jammers yield a net isotropic J/S of 82 dB. Results show convergence within 1-2 ? bounds for all elements of interest, except for the signal amplitude which exhibits a bias. Typical code-phase tracking steady-state accuracies are 1 m, carrier phase accuracies are .05 rad, carrier Doppler shift accuracies are .6 Hz, and DoA accuracies are .5 deg.
Published in:	Proceedings of the 31st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2018) September 24 - 28, 2018 Hyatt Regency Miami Miami, Florida
Pages:	4040 - 4051
Cite this article:	Esswein, Michael C., Psiaki, Mark L., "Vector Tracking of GNSS Signals from a Multi-Element Antenna," Proceedings of the 31st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2018), Miami, Florida, September 2018, pp. 4040-4051. https://doi.org/10.33012/2018.15876
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