L1 Carrier Phase Multipath Error Reduction Using MEDLL Technology

Abstract

In single frequency (Ll) GPS receivers, multipath is the dominant error source in differential carrier phase and pseudorange measurements. Consequently, it is the dominant error effecting DGPS positioning accuracy. The Multipath Estimating Delay Lock Loop (MEDLL) is a method for mitigating the effects due to multipath within the receiver tracking loops. The MEDLL does this by separating the incoming signal into its line-of- sight and multipath components. Using the line-of-sight component, the unbiased measurements of code and carrier phase can be made. In previous papers, the authors have demonstrated MEDLL performance in mitigating the effects of multipath on C/A code pseudorange measurements. Also, they have shown that it is possible to use the MEDLL derived parameters to calculate a multipath error correction for the carrier phase measurements. This carrier phase multipath correction has now been implemented in NovAtel’s MEDLL receiver. Using a GPS signal simulator, the carrier phase performance of the MEDLL receiver for a single multipath and a multiple multipath case was compared to a standard phase lock loop. The results showed the MEDLL receiver was able to substantially reduce the carrier phase multipath errors as compared to a standard NovAtel receiver.