Brief Study to Improve Robustness for RTK-GNSS with QZSS (Quasi-Zenith Satellite System)

Real-time kinematic Global Navigation Satellite System (RTK-GNSS) is a real-time satellite positioning system. The range from the user’s GNSS antenna, which is determined by the phase measurement of the carrier waves from the GNSS satellites, to the carrier waves from the GNSS satellites is precise to the millimeter level. Thus, an object's position, both horizontal and vertical, can be determined to within several centimeters. Research on the ambiguity resolution technique for RTK-GNSS has been ongoing around the world for a long time. In this work, the authors have attempted to resolve the ambiguity by using carrier phase raw data from two GPS receivers. It was demonstrated that it is possible to reduce the ambiguity and time to the first fix by selecting the optimal satellite combination for double phase difference. Double phase difference shapes the surface of the position of a rotary hyperboloid, focusing on two satellites’ locations in use. It was shown that the faster the rotary hyperboloid movement, the shorter the time to resolve ambiguity and the time to first fix. This is because the faster the rotary hyperboloid moves in space, and the smaller the ionospheric and tropospheric range error become, the easier it is to resolve the ambiguity from a real number to a fixed integer number. Usually, the pivot satellite is selected to calculate the double phase difference. Instead, two satellites within close geometric distance were selected for double phase difference. The pivot satellite was not selected. Furthermore, because the calculation performance by computers has increased, as many dependent multi-GNSS double phase differences were calculated as possible to improve robustness for RTK-GNSS after the lowest number of independent ambiguity was resolved. For this reason, the double phase difference includes the ionospheric and tropospheric range error. Thus, the all-integer ambiguities of many dependent double phase differences were resolved. Further, position continued to be fixed, even when the radio waves from satellites to vehicles in a skyscraper were received off and on. Finally, these research results can be used together with the current ambiguity resolution technique for RTK-GNSS.