Acquisition Performance Analysis for BOC Modulated Signals

The advent of the new European satellite navigation system Galileo and the current study of a new generation of GPS satellites are increasing the interest towards navigation related systems, services and applications. Both the systems foresee improved performances with respect to the present GPS C/A code, mainly achieved by using novel modulation schemes for the signals-In-Space. The Binary Offset Carrier (BOC) modulation, different (and longer) codes, and pilot channels have been proposed as a mean to reduce the mutual interference on common carriers, and also as a way to improve the expected performance. On the receiver side these system design choices have a relevant impact on the receiver architecture which as now to deal with different signals. One of the core techniques affected by these choices is certainly the acquisition stage, which has the goal to detect the presence of a certain satellite and to provide a rough estimation of the local code alignment and Doppler shift. This work will address the comparison of the acquisition schemes useful for acquiring the Galileo BOC modulated signals It is well known that several acquisition schemes for CDMA signals can be found in literature; many of them, however, are not suitable for navigation application where the signal to noise ratio is a critical parameter. These algorithms successfully adapted for GPS C/A code in the past must now be reviewed for the BOC modulated signal where the presence of side peaks in the correlation function can increase (if not properly processed) the probability of false alarm of the acquisition stage. Conventional serial search algorithms and FFT based algorithms on the basis of the system complexity, taking into account the number of quantization levels and acquisition accuracy (in terms of probability of false alarm) for different value of SNR will be studied. In order to compare the various acquisition systems and to identify the schemes that can be successfully used in the acquisition of Galileo signals, a simulation based analysis has been performed in order to identify the best acquisition schemes (and the relative parameters) that can work with the Galileo signals trading the receiver complexity with the expected performance