The reduction of multipath errors is a significant challenge in the Global Navigation Satellite System (GNSS), especially when receiving non-line-of-sight (NLOS) signals. However, selecting line-of-sight (LOS) satellites correctly is still a difficult task in dense urban areas, even with the latest GNSS receivers. This study demonstrates a new method of utilization of C/N0 of the GNSS to detect NLOS signals. The elevation-dependent threshold of the C/N0 setting may be effective in mitigating multipath errors. However, the C/N0 fluctuation affected by NLOS signals is quite large. If the C/N0 is over the threshold, the satellite is used for positioning even if it is still affected by the NLOS signal, which causes the positioning error to jump easily. To overcome this issue, we focused on the value of continuous time-series C/N0 for a certain period. If the C/N0 of the satellite was less than the determined threshold, the satellite was not used for positioning for a certain period, even if the C/N0 recovered over the threshold. Three static tests were conducted at challenging locations near high-rise buildings in Tokyo. The results proved that our method could substantially mitigate multipath errors in differential GNSS by appropriately removing the NLOS signals. Therefore, the performance of real-time kinematic GNSS was significantly improved.

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The Quasi-Zenith Satellite System (QZSS), Japanese positioning satellite constellation has two types of precise point positioning (PPP) services: centimeter-level augmentation service (CLAS) for land and multi-GNSS advanced demonstration tool for orbit and clock analysis (MADOCA). Currently, both CLAS and PPP correction data are broadcasted through the QZSS. It is highly good time to evaluate CLAS and PPP service in Japan. CLAS service has advantage in convergence time compared with PPP service. In the case of short gap like as overpasses, the convergence time is within 1 minute. The motivation of this research is to investigate the integration of CLAS or PPP results and our previous integration method using low-cost IMU/Odometer sensors. In reality, several commercial receivers capable of using CLAS or PPP correction services are already released in Japan. We used outputs of these receivers for absolute positions and loosely-coupled integration using Kalman filter is used to integrate them. The test data were obtained on the sea and expressway in 2019. Firstly, the performance of PPP and CLAS on the sea using the commercial receiver was evaluated. For the reference of these positions, normal RTK was obtained in parallel in this test on the sea. In the test on the expressway, POLSV was used in parallel to produce the precise positions as a reference. Looking at the test results on the sea, the fix rate of CLAS was from 63 % to 94. The standard deviation in horizontal was within 10 cm. On the other hand, the result of PPP was slightly worse than the result of CLAS. We didn't evaluate the integrated navigation on the sea because it was impossible for us to obtain the speed information from the ship for now. Looking at the test results on the expressway, the fix rate of CLAS was also good over 70 %. The navigation performance of this integrated system was analyzed. The horizontal accuracy including some GNSS outages was stable and the standard deviation of all horizontal errors was 0.35 m. The 99 percentile value for the absolute horizontal errors was 1.34 m. 99.57 % of all solutions were less than 1.5 m. With regard to the test results of PPP and integrated system on the expressway, the results were introduced in Pacific ION 2019.

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