Binary Offset Carrier (BOC) signal planned for future Global Navigation Satellite System (GNSS) improves better positioning accuracy and smaller multipath error. However, due to the multiple side peaks in the auto-correlation function (ACF) of BOC modulated signals, the receiver may false lock onto one of the side peaks in tracking. This false lock would then result in a fatal tracking error. In this paper, we propose an unambiguous acquisition method for composite BOC (CBOC) to solve this problem. It aims to reduce the side peaks of the ACF for CBOC modulated signals. It is based on combination of traditional CBOC correlation function (CF) with reference CF of unmodulated pseudorandom noise code (PRN code). First, we present that cross-correlation function (CCF) with unmodulated PRN code is close to the secondary peaks of the traditional CBOC. Then, we obtain an unambiguous correlation function by substracting traditional CBOC ACF from these CFs. Finally, the acquisition performance for CBOC signals is examined, and it is shown that the proposed method has better performance in Additive White Gaussian Noise (AWGN) than the traditional unambiguous tracking methods.

Keywords: CBOC signal, pseudo correlation function, unambiguous tracking, side-peak cancelation