GPS Receiver Simulation and Software Verification

Abstract

The GPS receiver is a receiver capable of tracking the signal from a Global Positioning System (GPS) satellite containing carrier and code tracking loops characterized by their bandwidth and order. A math model of a CPS receiver that uses Monte Carlo techniques to simulate the many effects to be modeled if one is to predict the performance of a GPS receiver when it is operating near its SNR threshold is described. Among these are: (1) predetection filter characteristics, (2) dynamic stress effects, (3) phase or frequency loop error characteristics, (4) envelope detector algorithm, (5) postdetection filtering characteristics, (6) code loop error characteristics, (7) noise sample generation with proper degree of correlation, (8) effect on carrier and code loops when carrier oscillator has a frequency error, (9) effect on carrier and code loops when code loop has a phase error, (10) sampled data effects on carrier and code loop filters and digital oscillators, and (11) threshold improvement as a result of narrower loop bandwidths when inertial aiding is possible. By imbedding a modified version of this GPS receiver model in an interactive software development tool, the verification of actual digital receiver software in a simulated real-time environment can be performed. The design, implementation, and use of such an interactive software development tool is described in the second half of this paper.