Global Navigation Satellite Systems (GNSS) has played a significant role in modern society. Its applications ranges from transportation, security, communication to entertainment. More recently, the use of GNSS for authentication has been investigated. As a part of an important segment in the societal infrastructure, the GNSS, however, is subject to threats due to interference, jamming, and spoofing. The countermeasures against such threats thus become crucial. Typically, an interference or jamming may incapacitate a GNSS receiver while a spoofer may mislead the receiver with unforeseeable consequence. The interference and jamming can be detected by observing the carrier to noise ratio and suppressed by spatial or spectral filters. In comparison, the countermeasures against spoofing is more challenging. The paper proposes a method to detect spoofing of publicly-known signals based on cross-correlation of unknown encrypted signals between two GNSS receivers. Different from the existing method, this cross-correlation is performed between two re-ceiver's quadrature channel correlator outputs. This development leads to a more robust scheme in detecting spoofing and authenticating GNSS signal. The proposed method remains functional even when two receivers' sampling frequencies are different. In addition, the proposed method is also shown to be beneficial in terms of data transmission for the implementation of real-time spoofing detection or authentication application. This proposed approach is demonstrated on the spoofing detection of GPS L1 signal and authentication of BeiDou satellite navigation system (BDS) B1 and B2 signals.

Keywords: GNSS, GPS, BDS, P-code, maximum correlation result