This paper addresses the use of generalized correlations in the context of High-Sensitivity Global Navigation Satellite System (HS-GNSS) receivers. Generalized correlations are also referred to as post-detection integration (PDI) techniques or simply as non-coherent integration methods. The contributions of this work are twofold. On the one hand, a novel PDI method is presented, which improves the performance of methods found in the literature for small errors of the frequency offset. On the other hand, an exhaustive comparative performance analysis is provided between the proposed technique and the existing ones in the presence of phase noise coming from the local oscillator. To this end, results have been obtained for two different clocks, namely a temperature compensated crystal oscillator (TCXO) and an oven-controlled crystal oscillator (OCXO). In both cases, the proposed technique outperforms the existing ones.

This paper addresses the problem of finding the optimal non-coherent detector or Post Detection Integration (PDI) technique to acquire weak signals in the context of High- Sensitivity Global Navigation Satellite System (HS-GNSS) receivers. This detector is derived using the Generalized Likelihood Ratio Test (GLRT) in the presence of data bits and variations in the carrier phase. The resulting detector is difficult to implement in practice because the amplitude of the signal must be known a priori. Two approximations of the resulting detector, which depend on the signal-to-noise ratio, are proposed, namely the Non-coherent PDI (NPDI) and non-quadratic NPDI (NPDInq) techniques. From this result, we prove that in general the NPDInq technique is the best option to detect weak signals in HS-GNSS receivers. In addition, a new statistical characterization of the NPDInq technique is proposed, which improves the approach used in the literature by applying the central limit theorem.

Intentional interference, and in particular GNSS spoofing, is currently one of the most significant concerns of the Positioning, Navigation and Timing (PNT) community. With the adoption of Open Service Navigation Message Authentication (OSNMA) in Galileo, the E1B signal component will continuously broadcast unpredictable cryptographic data. This allows GNSS receivers not only to ensure the authenticity of data origin but also to detect replay spoofing attacks for receivers already tracking real signals with relatively good visibility conditions. Since the spoofer needs to estimate the unpredictable bits introduced by OSNMA with almost zero delay in order to perform a Security Code Estimation and Replay (SCER) attack, the spoofer unavoidably introduces a slight distortion into the signal, which can be the basis of a spoofing detector. In this work, we propose five detectors based on partial correlations of GNSS signals obtained over predictable and unpredictable parts of the signals. We evaluate them in a wide set of test cases, including different types of receiver and spoofing conditions. The results show that one of the detectors is consistently superior to the others, and it is able to detect SCER attacks with a high probability even in favorable conditions for the spoofer. Finally, we discuss some practical considerations for implementing the proposed detector in receivers, in particular when the Galileo OSNMA message structure is used.