In this paper, we propose an efficient method for eliminating ambiguity in the acquisition and tracking processes of binary offset carrier (BOC)-modulated signals. Our contribution is realized in two stages. The first one is based on the use, at the receiver end, of optimized locally generated subcarrier sequences to get a completely unambiguous composite correlation function (CF). This first stage is used to initialize and control the second stage of the proposed method designed on the basis of a maximum likelihood algorithm (MLA) to mitigate, specifically, multipath (MP) effect. In fact, the idea is to combine, in this second stage, the received signal (affected by noise and MP) with a set of locally generated ideal BOC(m,n)-modulated signals, which are delayed and weighted by the MLA-estimated parameters of delays, amplitudes, and phases of all the MP signals, to obtain an unambiguous CF with better performance. The simulation results, based on MATLAB tool, have demonstrated that the proposed method effectively eliminates the ambiguity problem. Besides, a comparative study with several methods has shown that the proposed method grants better performance than the most popular techniques. K E Y W O R D S

No abstract

In Global Navigation Satellite System (GNSS) applications, the Binary Offset Carrier (BOC) modulation provides superior benefits vis-a-vis the classical Binary Phase Shift Keying (BPSK) one. Nevertheless, this modulation type presents a major drawback due to the presence of secondary peaks in envelope of the received signal Autocorrelation Function (ACF). This is due to the fact that the ACF side peaks may create false lock points in the Discrimination Function (DF) envelope of the Delay Locked Loop (DLL) structure, producing ambiguity in both acquisition and tracking processes. In the present paper, the Strobe Double Phase Estimator (SDPE) technique for multipath (MP) effect reduction is used in BOC modulated signals acquisition and its performance is analyzed and then enhanced by applying a proposed scheme that is efficient and valid for all BOC modulated signals. The suggested method is based on the use of the SDPE approach for coherent configuration in conjunction with the same approach for non-coherent configuration. As result, the ACF resulting from this combination is unambiguous. Besides, a large evaluative comparison between the new algorithm and the SDPE technique is achieved together with a performance evaluation of the proposed method in MP environment based on the Root Mean Square Error (RMSE) criterion. The obtained results have shown that our proposed scheme presents better performances in the presence of MP.

No abstract