# Assessment of IRNSS-Only Data Processing: Availability, Single-Frequency SPP and Short-Baseline RTK
## 5 Results and Analysis  
### Availability of Satellite Constellation  
This section focuses on the availability assessment of IRNSS constellation in terms of the visible satellite numbers, service rates, and PDOP values. For comparative analysis, the results of GPS-only and GPS/IRNSS cases are also provided. The precise ephemeris products of IRNSS are absent at present, and thus the assessment is based on the coordinates of IRNSS and GPS satellites calculated by the broadcast ephemeris. According to the strategies described in [PERSON] et al. (2020), the whole world can be divided into 72 \(\times\) 72 grids with a spatial resolution of 2.5\({}^{\circ}\) (latitude) by 5\({}^{\circ}\) (longitude), and the center of each grid is taken as the position for the virtual stations. The sampling interval is 30 s, and the elevation cut-off angle is set to 10\({}^{\circ}\). The availability of satellite constellation is evaluated by analyzing the relative geometry of virtual receivers and employed satellites. The assessment is based on the single-day data on 12 July 2019, with the view that the orbit repetition period is one day for both GPS and IRNSS satellites. The global distribution of the average number of visible satellites over a day for the IRNSS-only case is displayed in Figure 3. The IRNSS satellite signals cannot be received in a large elliptic region (marked in white in Figure 3), which is centered at 97.5\({}^{\circ}\) W on the equator, and extends from 40\({}^{\circ}\) W to 160\({}^{\circ}\) W, and from 77.5\({}^{\circ}\) S to 77.5\({}^{\circ}\) N. In the areas with 80\({}^{\circ}\)E on the equator as the center, the west and east sides extending to 60\({}^{\circ}\) E and 100\({}^{\circ}\) E, and the north and south sides extending to 57.5\({}^{\circ}\) N and 57.5\({}^{\circ}\) S, users can observe 6-8 IRNSS satellites. These areas cover the primary service areas of IRNSS. Usually, there are also at least four visible IRNSS satellites in the secondary service areas as a result of the configuration of the IRNSS constellation. The average number of visible satellites for the GPS-only and GPS/IRNSS cases is shown in Figure 4. For the GPS-only case, the average value of visible GPS satellites over the middle and low latitude regions (15\({}^{\circ}\) N-60\({}^{\circ}\) N and 15\({}^{\circ}\) S-60\({}^{\circ}\) S) is 8.8, which is less than that over the other areas with a statistic of 9.9. The GPS/IRNSS integration can significantly increase the number of visible satellites in the IRNSS primary service areas, which reaches 15.0-17.7, while the corresponding satellite number in the IRNSS primary and secondary service areas ranges from 12.3 to 17.7. Usually, the position determination is considered to be feasible when at least four satellites are visible, and the PDOP value is less than 25. The service rate is the percentage of the time span, during which the positioning service is available, over the total analysis period (a day). The global distribution of the service rate of the IRNSS-only case is shown in Figure 5. The areas where the positioning service is always unavailable are marked in white in Figure 5. The service rate of IRNSS-only case reaches nearly 100.0% in the primary service areas. The average service rate of IRNSS-only cases over the secondary service areas is 88.4%. In addition, the service rate of IRNSS-only case decreases with the increasing distance from the primary service areas. The service rate of GPS-only and GPS/IRNSS cases is presented in Figure 6, which shows that the service rate for the two cases reaches 100.0% worldwide. Figure 3: Average number of visible satellites for IRNSS-only case. Figure 4: Average number of visible satellites for GPS-only and GPS/IRNSS cases. Figure 5: Service rate of IRNSS-only case (unit: %). Figure 6: Service rate of GPS-only case and GPS/IRNSS case (unit: %).