Multipath in GPS navigation and positioning

Abstract

In GPS-based positioning and navigation, there are several error sources. Among them, multipath is by far the most obstinate factor that jeopardizes the accuracy and reliability of satellite-based positioning and navigation. Multipath is regarded as the delay in the line-of-sight signal from a transmitting satellite due to reflection or diffraction caused by surrounding objects near the observation site. As a result, the reflected or diffracted signals are phaseshifted with respect to the originally transmitted signals. Consequently, the distorted signals result in degraded positioning and navigation solutions. Multipath influences cannot be easily eliminated or cancelled through differential positioning or modeling because of the sophisticated scenarios and mechanisms, even if great efforts are made to reduce errors. So far, strategies for dealing with this influence can be classified as hardware and software solutions, as well as multipath mitigation by careful observation of site selection. The former includes design improvement of both the GPS/GNSS receiver and their antennas. The patented MEDLL technique, the narrow cross-correlator, wideband tracking technology, antenna array, and digital-beaming steering are all examples of hardware developments. Software processing can be categorized as geometrical modeling, time domain modeling, frequency domain analysis, and comprehensive spectrum processing. Software processing and hardware design for multipath mitigation coexist and are mutually promoted. It is noted that the International Association of Geodesy (IAG) has established a special study group, SSG 1.182, in for multipath research, which is chaired by Dr. Mike Stewart from the School of Spatial Sciences, Curtin University of Technology, Australia (http://www.cage.curtin.edu.au/ mike/ssg1.182/members.htm). The objectives of the SSG 1.182 group are to study GNSS multipath detection and mitigation techniques with the aim of improving existing high-precision positioning accuracies, and to provide information and guidelines for multipath detection and mitigation to facilitate high precision applications. The group has provided a comprehensive reference list for multipath studies: http://www.cage. curtin.edu.au/ mike/ssg1.182/biblio.htm. In addition to this, the following is a collection of selected Websites that give information about GPS multipath hardware and software research.