# GNSS Multipath Detection Using Continuous Time-Series C/N0
## 2 Features of Measured C/N\({}_{0}\) in Dense Urban Areas
### Measured C/N\({}_{0}\) in Dense Urban Areas  
To investigate the characteristics of C/N\({}_{0}\) in dense urban areas, we obtained raw measurements near high-rise buildings in Tokyo. The configuration of the target location is illustrated in Figure 2. The right side of the figure shows the 3D Google map, and the red circle represents the GNSS antenna location. The left side of the figure shows the 2D Google map and the height information of the surrounding buildings at this location. In this figure, the top denotes the north. As can be observed from Figure 2, it was likely that NLOS signals would be received from the higher buildings on the azimuth of 290\({}^{\circ}\). Data from the GPS, GLONASS, BDS, QZSS, and Galileo were recorded on a street near Tokyo Station in a typical urban-canyon area for 30 min from 8:15:00 GPS time (GPST) on April 3, 2020. A u-blox F9P, which is a low-cost dual-frequency receiver with a standard patch antenna, was used to record the data at 1 Hz. These data were also used to verify the pseudo-range residuals. Figure 3 presents the sky plots of all satellites over a 15\({}^{\circ}\) mask angle at 8:25:00 GPST and the condition of the satellites. A 3D map was also used in this case to specify the multipath types of all satellites. The satellite position and estimation of the radio wave propagation path were calculated using previously developed software known as GPS-Studio [16]. In this study, the accuracy of the 3D map data GEOSPACE3D was approximately 1.5 m, and the map did not include trees and signs. The building shapes in the study area were nonuniform in the height direction. Hence, the building shape was modified for this study using GIS software called QGIS to prevent incorrect estimation of the propagation path. Modifications were made within a circle with a radius of 500 m that was centered on the antenna under evaluation. In Figure 3, the white and black circles indicate the blocked  
Figure 1: Three multipath types in Global Navigation Satellite System (GNSS). or NLOS satellites, whereas the red circles indicate the LOS satellites. The four satellites GPS 01, QZSS 03, Galileo 01, and BDS 07 were selected to demonstrate the temporal C/N\({}_{0}\) of the L1 band for 30 min as LOS signals. We selected these four satellites because these they were clearly regarded to receive LOS signals all the time based on a 3D map. Moreover, the four satellites GPS 22, GPS 27, GPS 30, and GLONASS 02 were selected to demonstrate the temporal C/N\({}_{0}\) of the L1 band for 30 min as NLOS signals because these four satellites were clearly regarded to receive NLOS signals all the time based on a 3D map. Figure 4 shows the temporal C/N\({}_{0}\) mainly receiving LOS signals. Figure 5 shows the temporal C/N\({}_{0}\) mainly receiving NLOS signals. TOW represents time of week in GPST. As can be observed from Figure 4, the C/N\({}_{0}\) of the LOS signals did not fluctuate substantially, with the exception of Galileo 01. The C/N\({}_{0}\) value of Galileo 01 was first affected by diffraction and then received LOS + reflected signal for a certain time. As can be observed from Figure 5, the C/N\({}_{0}\) of the NLOS signals fluctuated strongly in all satellites. In fact, other satellites that recognized NLOS reception, which are not shown in Figure 5, exhibited a similar tendency. The LOS signals of GPS 22, GPS 27, and GLONASS 02 were clearly blocked by the buildings on the azimuth of 110\({}^{\circ}\). However, the C/N\({}_{0}\) values of the three satellites were mostly sufficient to track the carrier phase measurements over approximately 30 dB-Hz. More importantly, stable C/N\({}_{0}\) could not be observed owing to the specular reflection, despite these signals of the three satellites clearly being reflected by the tall building on the azimuth of 290\({}^{\circ}\). This indicates that the diffracted signal owing to the building on the azimuth of 110\({}^{\circ}\) could be received with NLOS signals (reflected by the building on the azimuth of 290\({}^{\circ}\)) simultaneously.