CFAR detectors for hybrid-search acquisition of Galileo signals

The acquisition of code phase and frequency shift is a pre-requisite for any Code Division Multiple Access (CDMA) system. One important step in the acquisition process is the choice of a suitable decision variable and of an appropriate threshold, which will determine the probabilities of detection and false alarm. In serial-search strategies and in many hybrid-search strategies proposed in literature so far, the decision variable is typically equal to the squared absolute value of the averaged correlator output, and, in order to achieve a Constant False Alarm Rate (CFAR), the threshold is set adaptively, according to the Carrier-to-Noise Ratio (CNR) and to the channel fading statistics. Alternatively, thresholds which are independent on CNR and channel fading statistics may be found, if the decision variable is built in a suitable manner. In this paper, we compare and analyze three CFAR detectors for hybrid-search acquisition of a Binary-OffsetCarrier (BOC) modulated CDMA signal, which are independent on CNR. The traditional decision variable and its associated threshold are also kept as benchmarks. The comparison is done in terms of detection probability and of the dependence of the threshold on the channel conditions. We also show which of the proposed CFAR detectors is the most robust to noise and channel conditions.