Codeless Angular Estimation via Array Receiver for GNSS Situation Awareness

Chun Yang, Andrey Soloviev

Peer Reviewed

Abstract:	In navigation warfare, a jamming attack is rather easy to detect whereas that of spoofing is more subtle. Spoofing may be preceded by a strong jamming, which interrupts the operation of a receiver and forces it back to signal search. At that point, an unprepared receiver is likely to fall victim to acquiring the dominant signals that happen to be the stronger spoofing ones. One way to assess the presence of spoofing for GNSS situation awareness is through estimating the spatial distribution of signal sources in the GNSS bands in which a spoofer has no means to hide its own physical presence while masking authentic GNSS signals. Indeed, a GNSS receiver equipped with a controlled reception pattern antenna (CRPA) can estimate the direction of arrival (DOA) of GNSS signals and ascertain if it originates from a legitimate direction or otherwise. For GNSS signals, be it authentic or spoofing, post-correlation angular estimation can be applied to the prompt correlators of tracking channels, one for each array element, when the pseudorandom number (PRN) codes are known. Angular estimation methods include the Bartlet beamformer, Capon beamformer, multiple signal classification (MUSIC), and iterative adaptive array (IAA). For those GNSS signals without their PRN codes, codeless tracking can be used, which strips off the unknown code signs via signal squaring or cross-correlation of signal components. Even though the post-correlation angular estimation methods remain applicable, they face an ambiguity issue arising from phase (and frequency) doubling when squaring the signals. That is, wrapping (2?-modulo) a doubled angle is a nonlinear mapping akin to a hash function difficult to reverse. In this paper, we present a novel method of codeless angular estimation of signals via array receiver (CAESAR) that avoids phase-doubling ambiguity. It consists of five key steps, namely, (i) remove all the unknown PRN codes by squaring the received signal, (ii) estimate the doubled frequency of the underlying satellites in the squared signal, (iii) isolate each signal by its Doppler frequency estimate, (iv) conjugate-multiply across the array elements, and (v) perform angular estimation. Note that the cross-correlation across the array elements in (iv) removes PRN code signs without phase doubling while generating the desired relative phases without ambiguity for angular estimation in (v). Angular estimation with an array antenna for GNSS signals is first discussed for the post-correlation and codeless tracking settings. The phase doubling effect that creates ambiguity in angular estimation is then analyzed. The proposed CAESAR method is next formulated in detail. Test results are presented to illustrate the functionality and performance of codeless angular estimation that can be used for GNSS situation awareness.
Published in:	Proceedings of the 2026 International Technical Meeting of The Institute of Navigation January 26 - 29, 2026 Hyatt Regency Orange County Anaheim, California
Pages:	749 - 771
Cite this article:	Yang, Chun, Soloviev, Andrey, "Codeless Angular Estimation via Array Receiver for GNSS Situation Awareness," Proceedings of the 2026 International Technical Meeting of The Institute of Navigation, Anaheim, California, January 2026, pp. 749-771. https://doi.org/10.33012/2026.20550
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