# GNSS Multipath Detection Using Continuous Time-Series C/N0
## 3 Proposed Strong Multipath Detection Using C/N\({}_{0}\) Information
### Method to Determine the Threshold and Period
Therefore, no information was available for the second and third longest periods. For GLONASS 16, large pseudo-range errors occurred in the final 30% of the duration when C/N\({}_{0}\) decreased below 30 dB-Hz. For the remaining 70% of the duration, C/N\({}_{0}\) was high and the pseudo-range errors were small. Therefore, no information was available regarding the continuous period over the threshold. As can be observed from Table 2, the longest period in total was 164 s for GPS 22, and the second longest period in total was 163 s for GLONASS 02. These two satellites were affected by strong NLOS signals from the tall building on the azimuth of 290\({}^{\circ}\), as illustrated in Figures 2 and 3. Figure 9 presents the case of the temporal C/N\({}_{0}\) for GPS 22 with the elevation-dependent threshold, in which the three longest periods according to both C/N\({}_{0}\) and the proposed threshold are depicted. Furthermore, GPS 08 and Galileo 21 were also affected by strong NLOS signals from the tall building on the azimuth of 290\({}^{\circ}\). Therefore, the longest periods forboth satellites were over 80 s. Conversely, the C/N\({}_{0}\) of the satellites that received continuous strong NLOS signals decreased below the threshold determined according to the above at least approximately every 160 s. The main reason for this is that the diffracted signal from the building on the azimuth of 110\({}^{\circ}\) was actually received to the antenna simultaneously. Another possible explanation is that the reflectance of the wall of the building on the azimuth of 290\({}^{\circ}\) changed according to the reflected point. Based on these results presented in Table 2, if we set the period that should not be used for positioning to approximately 180 s, we could mostly remove these satellites with large pseudo-range errors from the positioning in the case of these data. However, the suitable period will change according to several factors, such as the distance between the antenna and surrounding buildings, the reflection, and diffraction degrees. Therefore, we need to set the period in which the satellite is not used for positioning to at least 180 s. For example, if the distance between the antenna and building reduces, the period of fluctuation owing to the multipath becomes long. Examining this test configuration, it is clear that the distances between buildings are large. Therefore, according to the test configuration, the period should be set to much longer than 180 s. In this study, we used 240 s as the period and compared the results when changing the period to 180 and 300 s. Moreover, the remaining large pseudo-range error could be detected using the normal residual check in the least-squares method. With this proposed method, it is important to balance the number of available satellites for positioning because at least four satellites are required for positioning. With the advent of multiple GNSS in recent years, numerous satellites are available even in dense urban areas. Furthermore, low-cost multi-frequency and multi-GNSS receivers have emerged. Therefore, we can focus on removing the satellites with large pseudo-range errors from positioning without significant hesitation. Figure 8: Relationship between elevation angle and C/N\({}_{0}\), and proposed threshold (GPS L1-C/A).