BPSK-like Methods for Hybrid-Search Acquisition of Galileo Signals

Abstract

The Binary Offset Carrier (BOC) modulation which has been proposed for future Galileo and GPS M-code signals, provides a higher spectral separation from BPSK-modulated signals, such as GPS C/A code. The absolute value of the auto-correlation function of a BOC signal has a narrower main lobe, which may increase the resolution of delay estimates, but also presents deep fades, which may lead to a higher number of timing hypotheses to acquire the signal. In order to get rid of these ambiguities, several approaches have been proposed in literature, which provide an unambiguous BPSK-like shape of correlation function. In this paper we analyze, compare and develop further two BPSK-like methods which allow to acquire a BOC-signal unambiguously. The focus is on hybrid search, where several time-frequency bins are searched in parallel. We introduce here a modified version of a BPSK-like method which decreases the receiver complexity and is valid for both odd and even BOC orders. We analyze both single-side band (SSB) processing (i.e., only one band is used) and dual-side band (DSB) processing (i.e., upper and lower bands are combined non-coherently). While eliminating the ambiguities in auto-correlation function, both SSB and DSB processing present some performance degradation, induced by the band selection and non-coherent processing. The analysis is done in the presence of multipath fading channels. As a benchmark, we keep also the ambiguous BOC processing. We consider parameters specified in the proposals for Galileo system Open Service (OS), respectively Publicly Regulated Service (PRS).