Evaluation of the effect of multipath on Global Positioning System (GPS) performance via GPS simulation

In this study, Global Positioning Satellite (GPS) simulation is employed to study the effect of multipath on two handheld GPS receiversGarmin GPSmap 60CSx (evaluated GPS receiver) and Garmin GPSmap 60CS (reference GPS receiver). Both GPS receivers employ the GPS L1 coarse acquisition (C/A) signal. Based on the results of this study, it is found that the decrease in number of visibles satellites due to physical obsructions and increase in number of multipath signals cause increase in probable error values, due to decreasing carrier-to-noise density (C/N0) levels for GPS satellites tracked by the receiver. In addition, the differences between horizontal positioning error (HPE) and vertical positioning error (VPE) values increase due to the removal of satellites above the horizon, while overhead satellites are maintained. Varying probable error patterns are observed for readings taken at different times. This is due to the GPS satellite constellation being dynamic, causing varying GPS satellite geometry over time, resulting in GPS accuracy being time dependent. The repeatability of multipath at stationary sites when GPS satellites are in the same positions during each orbital pass (approximately 11 min, 58 s) allows for corrections to be generated based on history of multipath occurances over time