Multipaths of the GPS signal reaching the GPS receiver lead to undesirable tracking errors and inaccurate ranging information. In this paper, we consider the multipath effect on noncoherent early-minus-late power discriminator. Analytical treatment of the effect of the carrier phase offset of the multipath relative to the direct path on the GPS receiver performance is provided. Compared with the well-known coherent discriminator, the noncoherent discriminator presents different tracking accuracy and sensitivity to multipath delay, magnitude, and phase. The paper considers the front-end precorrelation filter, which is typically applied to remove out-of-band interference and noise. Selections of suitable precorrelation filter bandwidth in conjunction with the early-late correlator spacing can aid in mitigating the multipath impeding effects on delay lock loop (DLL) and receiver discriminators. Computer simulations of the impact of a dominant multipath on the discriminator tracking performance are provided. It is assumed that the early and late correlations are performed within the same navigation symbol, and no symbol transitions are encountered over the correlation interval.
Proc. SPIE. 5819, Digital Wireless Communications VII and Space Communication Technologies
KEYWORDS: Error analysis, Global Positioning System, Signal to noise ratio, Receivers, Optical correlators, Statistical analysis, Interference (communication), Monte Carlo methods, Correlation function, Quantum efficiency
The use of GPS has broadened to include mounting on or inside manned or autonomous vehicles which makes it subject to interference generated from motor emissions. Many sources of interference are typically modeled as impulsive noise whose characteristics may vary in terms of power, pulse width, and pulse occurrences. In this paper, we examine the effect of impulsive noise on GPS delay lock loops (DLL). We consider the DLL for the GPS Coarse Acquisition code (C/A), which is used in civilian applications, but also needed in military GPS receivers to perform signal acquisition and tracking. We focus on the statistics of the noise components of the early, late, punctual correlators, which contribute to the discriminator error. The discriminator noise components are produced from the correlation between the impulsive noise and the early, late and punctual reference C/A code. Due to long time averaging, these components assume Gaussian distributions. The discriminator error variance is derived, incorporating the front-end precorrelation filter. It is shown that the synchronization error variance is significantly affected by the power of the received impulsive noise, the precorrelation filter, and the sample rate.