Innovations-based code discriminator for GPS/Galileo BOC signals

Binary offset carrier (BOC) modulation was considered for modernized military GPS and for the European navigation system, Galileo. Although it performs better than conventional BPSK modulation, the BOC waveforms have autocorrelation functions with multiple peaks that lead to potential tracking ambiguities. We propose to minimize this problem with a bank of extended Kalman filters (EKF) that tracks the phase/frequency from the quadrature components of the incoming signal. The code discriminator is a weighted sum of code delays with the weights being nonlinear functions of the EKF innovations. When compared to the early-late power discriminator, the proposed algorithm is much less prone to lose the tracking of the BOC autocorrelation main peak.