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Mitigation of false locks in the acquisition of high-order BOC signals in HS-GNSS receivers

This paper addresses the problem of acquiring weak high-order binary offset carrier (BOC) signals in the context of high-sensitivity global navigation satellite system (HS-GNSS) receivers. The use of high-order BOC modulations provides an improvement over conventional BPSK modulation in terms of positioning accuracy, at the cost of secondary peaks appearing in the correlation function. The acquisition of the main peak is a critical problem because the presence of secondary peaks often introduces a bias in the time-delay estimation. This problem is even more complicated to address when the signal is received with a low carrier-to-noise ratio. In this situation, we must resort to Post-Detection integration (PDI) techniques to acquire the received signal, and after that an estimator can be applied to identify the main correlation peak. The contributions of this work are twofold. Firstly, we analyze the performance of PDI techniques such as the Non-coherent PDI and the Differential PDI to acquire weak high-order BOC signals in static and dynamic channels. Secondly, after detecting the signal by using a PDI technique, we propose to apply the Maximum Likelihood (ML) and the Least Square (LS) estimators to estimate the time-delay of the main peak.