A Practical Approach to the Reduction of Pseudorange Multipath Errors in a Ll GPS Receiver

Abstract

The reduction of multipath biases on GPS measurements has traditionally been achieved through innovative antenna design, such as choke ring ground planes, and careful antenna site selection. These methods, although effective, are not always practical, especially in a kinematic environment. The implementation of Narrow Correlator mspacing design in GPS receiver code tracking loops has greatly reduced the multipath bias and the measurement noise on C/A code pseudorange measurements. Even with these advancements the bias due to multipath is still dominant in GPS position calculations. This paper introduces a new tracking loop which takes full advantage of the Narrow CorrelatorT5t spacing design, but in addition, is much more resistant to multipath effects on the correlation function and thereby reduces the multipath bias on the pseudorange measurements. The theory behind this new tracking loop design is presented along with its implementation into existing receiver hardware. Test results from a prototype receiver are presented. They show a 25 to 50 percent reduction of multipath error effects in the DGPS position solution as compared to a standard narrow correlator receiver.