CSAC-Aided GPS Multipath Mitigation

This paper introduces a method for GPS multipath mitigation using a chip-scale atomic clock (CSAC). A CSAC provides a stable, accurate timing source to a GPS receiver. Because the clock on a GPS receiver is typically not synchronized to the GPS satellite clocks, there is a difference between the two clocks, which is called a timing bias. Since a typical GPS solution requires solving for 3D position and a timing bias, at least four GPS satellites must be in view to get a time and position solution. Using the CSAC, the initial timing bias will be solved for, and future measurements of the timing bias will be computed. When the measurements exceed a certain threshold, at least one of the satellites in view has been corrupted by multipath. Then a solution involving only fewer satellites than are in view will be solved for. Baseline testing was done in clear sky in an open field at Auburn University. Multipath testing was also done with antennas on a test vehicle in downtown Atlanta, an area known to be an urban canyon with high instances of multipath, as well as around downtown Auburn, where multipath is possible, but not as detrimental as in downtown Atlanta. The algorithm's ability to navigate using only three satellites Finally, the proposed technique will be compared to other multipath algorithms developed at Auburn University, which include angle-of-arrival (AOA) and carrier-phase residual techniques.