Analysis and Verification to the Effects of NH Code for Beidou Signal Acquisition and Tracking

The conventional acquisition and tracking strategies may be effected for the reason that the NH code is added to the modern GNSS signals. Based on the signal model, this paper illustrated the frequency discriminator's working principle in the GNSS receiver, and verified that when the navigation data bits are modulated by the NH code, the tracking loop should choose a frequency discriminator which is insensitive to data bit transition. By analyzing the probability density function of the integration magnitudes and the effect of frequency error to the integration magnitudes, this paper drew a conclusion that before tracking the modern GNSS signals, the searching process should acquire more precise Doppler frequency estimation. Software and hardware receiver tests showed that the new GNSS signal should be tracked by the two-quadrant discriminator and precise estimation is needed, otherwise the four-quadrant discriminator will lock in a wrong frequency and the two-quadrant discriminator will lose lock.