GPS Multipath Detection and Mitigation Timing Bias Techniques

Abstract

In this thesis, timing-based methods of multipath mitigation and detection are developed. GPS pseudorange measurements are used to calculate a receiver's position and timing bias, which is a measurement of the di erence between the GPS satellite clocks and receiver clock. The timing bias will be monitored while the receiver is disciplined with a chip-scale atomic clock (CSAC), which has exceptional stability and accuracy, and has recently been made available to the public at an a ordable cost. The CSAC controls the receiver's timing bias drift rate, allowing for the use of the timing bias to detect multipath and spoo ng. Under normal operation, the clock in a GPS receiver drifts too rapidly to be used for multipath detection, and must the timing bias must always be solved for as a nuisance parameter. Di erent grades of clocks will be examined in a benign environment to attain accurate models of the speci c clocks being used, and to determine what the clock drifts are without external in uences. The clock models will then be used to detect multipath in a dynamic test. After detection, an algorithm to remove faulty GPS signals will be implemented, creating an accurate, multipath-free position solution. In addition to detecting multipath, the clock model will provide a reasonable estimate of the clock drift when there are fewer than four satellites available. This allows for a reduction from four to three satellites needed to solve for position, as well as the ability to predict clock drift during a GPS outage. Finally, a spoo ng simulation will be outlined and simulated using a low-cost ublox receiver. The ublox clock is not as good as a CSAC, but performs acceptably for determining whether or not the receiver is being spoofed.