# GNSS Multipath Detection Using Continuous Time-Series C/N0
## 3 Proposed Strong Multipath Detection Using C/N\({}_{0}\) Information
### Flowchart of the Proposed Method  
Figure 10 depicts the flowchart of our proposed method, where our new approach is indicated in the gray-colored part. The detection method of LOS or NLOS is detailed in this part. Positioning software developed by our laboratory was used. The core part of the program was considerably similar to RTKLIB, and we modified certain functions such as the satellite selection to include the new concept. We also used velocity information deduced from the Doppler frequency [17]. RTKLIB is an open-source program package for standard and precise positioning with the GNSS [18]. First, GNSS observation data from both the base station and rover station were input. Thereafter, several satellite selection methods were performed. Both the pseudo-range and carrier phase measurements had to be generated from the receiver. Furthermore, half-cycle ambiguities had to be resolved in the case of the RTK-GNSS. The flag for this half-cycle checking from the receiver could be used for this purpose. The normal mask angle and required minimum C/N\({}_{0}\) were set for both the base station and rover station. The mask angle was set to 15\({}^{\circ}\). The value of the minimum C/N\({}_{0}\) for the L1 band (GPS and QZSS L1-C/A, GLONASS G1, Galileo E1, and BDS B1) was set to 32 dB-Hz, which is actually the minimum C/N\({}_{0}\) for all GNSS obtained in the open sky condition when the mask angle is set to 15\({}^{\circ}\). Furthermore, the value of the minimum C/N\({}_{0}\) for the L2 band (GPS and QZSS L2C, GLONASS G2, Galileo E5B, and BDS B2) was  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**SV**} & **90 th Percentile** & **Percentage of** & **Longest Period** & **Second** & **Third Longest** \\  & **of All Errors** & **C/N\({}_{0}\) \textgreater{}40** & **(s)** & **Longest Period** & **Period** \\  & **(m)** & **(\%)** & **(s)** & **(s)** & **(s)** \\ \hline G03 & 150.5 & 4.1 & 79 & 67 & 59 \\ G08 & 61.9 & 28.5 & 89 & 64 & 63 \\ G22 & 99.6 & 64.1 & 164 & 140 & 134 \\ G27 & 111.4 & 6.7 & 149 & 127 & 86 \\ G28 & 73.8 & 0 & 12 & 7 & 5 \\ G30 & 90.5 & 3.3 & 108 & 13 & 13 \\ J01 & 175.5 & 0 & 117 & 102 & 81 \\ E13 & 121.1 & 0 & 85 & 63 & 54 \\ E21 & 115.2 & 6.9 & 137 & 103 & 96 \\ E31 & 30.2 & 27.6 & 17 & - & - \\ E33 & 79.4 & 0 & 74 & 12 & 10 \\ R02 & 154.5 & 36.2 & 163 & 130 & 109 \\ R16 & 55.2 & 62.7 & - & - & - \\ R19 & 242.6 & 0 & 42 & 40 & 31 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Summary of continuous periods over threshold for selected satellites.  
Figure 9: Real C/N\({}_{0}\) for GPS 22 with elevation-dependent threshold and three longest periods.  
also set because we could expect multi-frequency diversity [19]. As the wavelength differed for the L1 band and L2 band frequencies of the same satellite system, the fluctuation period of C/N\({}_{0}\) owing to diffraction or reflection was different for the L1 band and L2 band. The minimum C/N\({}_{0}\) for L2P of the GPS was not checked because the u-blox F9P receiver does not output L2P signals. For the rover station, after applying these normal settings as in the base station, the time-series C/N\({}_{0}\) values were checked in terms of the threshold and period based on our proposed method. Subsequently, the residuals of the satellites in the least-squares method were checked. If the absolute residual of the satellite was the maximum and over 10 m, the satellite was repeatedly removed from the positioning provided that the HDOP was lower than 10. Finally, we processed these measurements to obtain the DGNSS and RTK-GNSS solutions. We compared the performance with or without checking the time-series C/N\({}_{0}\) based on our new approach. The other settings mentioned in the above remained exactly the same.