RTK-GPS Reliability Improvement in Dense Urban Areas

The use of GNSS technology in urban areas is expected to increase. Since there are many buildings in such areas, the signal from a satellite is occasionally reflected or diffracted [1]. This leads to considerable multipath errors, and it is important to improve the reliability of GPS for the future ITS. For the safe use of GPS, positioning errors must be small, and it is necessary to know whether the errors exceed the threshold or not. To increase the reliability, it is important to detect inferior observations. The objective of this study is to improve the reliability and availability of RTK-GPS. We reveal the relationships between reliability and availability by performing a quality check on the GPS observation data. For example, the reliability decreases considerably when the number of usable satellites in RTK-GPS is four rather than five or more. We also propose an efficient signal-quality test for RTK-GPS on the basis of C/N0 (the carrier-to-noise ratio) to remove inferior GPS observations. We demonstrate the success of our method using raw GPS data obtained in dense urban areas.