Ultra-wideband Radio Aided Carrier Phase Ambiguity Resolution in Real-Time Kinematic GPS Relative Positioning

Abstract

In this thesis, ultra-wideband radios (UWBs) are integrated into the real-time kinematic (RTK) algorithm using differential GPS techniques to achieve a highly precise relative positioning vector between GPS antennas. This has potential applications including an autonomous leader-follower scenario or an unmanned aerial refueling scenario. The UWBs give a range measurement between antennas, while the RTK solution gives a three dimensional relative positioning vector. This UWB range measurement can be integrated into the RTK algorithm to add robustness and increase accuracy. When two GPS receivers are within a close proximity, most of the errors that degrade the GPS signal are correlated between the two receivers and can be mitigated by using differential techniques. This can be done using either a static base station, as is the case for RTK, or using a dynamic base, as is the case for DRTK. These algorithms are explained in detail in this thesis, as well as results showing the improved accuracy. The difficulty of the RTK algorithm is that it must resolve ambiguities in the carrier phase once the receiver has locked on to a satellite’s signal. The least squares ambiguity adjustment (LAMBDA) method was created to help resolve these ambiguities. When the baseline between GPS antennas is known, this known baseline can be used as a constraint and can be integrated into the LAMBDA method, resulting in a C-LAMBDA method. This thesis uses the UWB range measurements in place of the known baseline in the C-LAMBDA method and results showing its improvement over the standard LAMBDA method are presented. By looking at the experimental results, some conclusions can be made. As long as the accuracy of the UWB range measurements is within a few centimeters, it is shown that it can be used in the C-LAMBDA method as the baseline constraint in helping to resolve the carrier phase ambiguities.