In this paper, we propose a novel signal modulation technique, Variable Binary Offset Carrier (V-BOC) for next-generation Global Navigation Satellite System (GNSS). The proposed modulation technique is based on the BOC signal that shifts the center frequency of the signal using a square wave and the Chirp signal that changes the frequency of the carrier wave over time, which discretely increases and decreases the frequency of the BOC signal over time. The auto-correlation (ACF) envelope of the V-BOC signal that is generated by selecting an adequate internal parameter in the proposed modulation technique shows a much sharper main lobe and a smaller secondary lobe than the conventional modulation technique’s envelopes such as Binary Phase Shift Keying (BPSK) and BOC signals. This characteristic can reduce the possibility of the receiver estimating erroneous code-locks in a signal tracking step in a multipath channel environment in an urban area where the time difference between Line of Sight (LOS) and None Line of Sight (NLOS) is very short. In addition, next-generation GNSS signals are highly likely to be affected by interference from numerous GNSS signals occupying the same band. Since the center frequency of the modulated signal is shifted by changing the frequency of the BOC signal according to time, the interference effect of other GNSS signals sharing the same band is very small. We use the Early-Late (EL) Discriminator, which is widely used in conventional receivers, to compare BPSK, BOC technique with code-lock performance to prove robustness in multipath environment. Moreover, we analyze Spectral Separation Coefficient (SSC) with signals in L1 band for interference effects from other GNSS signals. |
