Using GPS Multicorrelator Receivers for Multipath Parameters Estimation

The performance of GPS may be degraded by many perturbations such as jamming, the effects of the ionosphere, and multipath. Many studies have been done to reduce the effect of multipath on the GPS measurements. Some of these are based on the radiation pattern of the receiving antenna, while most of them concentrate on the characteristics of the receiver tracking loops. A well-known implementation enabling the characterization of multipath effects on the tracking loops through the analysis of the shape of the correlation peak using a multicorrelator receiver has been proposed in [ 1 ]. The widespread use of multicorrelator receivers gave us the idea to try our own implementation of an identification and mitigation technique. The aim of the proposed paper is to describe a least squares method to identify different multipath parameters using multicorrelator outputs, and to present results of the application of this technique. The paper starts with a brief review of the impact of several reflected rays on the code and phase tracking loops. Then, the principle of multicorrelator receivers is described, and the particular structure of the multicorrelator firmware of the NovAtel Millenium receiver is given as an illustration. After this, the least squares technique used to estimate the relative amplitude, relative code and phase delays, code and phase tracking errors is presented. Results of the application of this technique on real data collected on a real receiver connected to a Spirent GPS generator are shown. These results illustrate the overall good performance of the method and its limitations. Finally, a conclusion is drawn on this technique and its possible capacity to improve the performance of tracking loops by removing multipath components in correlator outputs.