# Assessment of IRNSS-Only Data Processing: Availability, Single-Frequency SPP and Short-Baseline RTK
## 7 Conclusions  
Currently, the IRNSS has eight in-orbit satellites, and has the preliminary capability to provide the standalone navigation and positioning services in the service areas. This contribution investigates the current status of IRNSS single-system data processing, including the availability (i.e., the number of visible satellites, the service rate, and the PDOP value), the single-frequency SPP performance, and the single-frequency short-baseline RTK positioning performance. For comparative analysis, the results of the GPS single-system case and the GPS/IRNSS dual-system combination case are also provided. The datasets from 14 MGEX stations spanning a week from 7-13 July 2019 are employed. Regarding the theoretical availability of IRNSS constellation under a cut-off elevation angle of 10\({}^{\circ}\), there are 6-8 visible IRNSS satellites in its primary service areas, and at least four IRNSS satellites can be tracked in the secondary service areas. The service rate of IRNSS-only cases in the primary service areas is nearly 100.0%, and the corresponding average value over the secondary service areas can still be up to 88.4%. The average PDOP value of IRNSS-only cases fall between 3.3 and 6.2 in the primary service areas, and is usually less than 15 in the secondary service areas. The GPS/IRNSS dual-system  
Figure 16: Distribution of carrier phase observation residuals of ambiguity-fixed solutions derived from GPS/IRNSS integrated short-baseline RTK for GPS and IRNSS satellites. combination can significantly increase the number of visible satellites and reduce the PDOP value in the IRNSS service areas. The positioning accuracies of the IRNSS single-system SPP are 6.031, 6.015, and 9.668 m in the east, north, and up directions, respectively, and those of the GPS single-system SPP are 0.519, 0.815, and 2.293 m in the three directions, respectively. The GPS/IRNSS dual-system combined SPP can improve the 3D positioning accuracy by 10.1% and 82.6% over the GPS-only and IRNSS-only cases, respectively. The RMS statistics of code observation residuals derived from the GPS/IRNSS integrated SPP solutions are 1.203 and 0.808 m for the IRNSS and GPS satellites, respectively. The time series of single-epoch ISB estimates between IRNSS and GPS (in the GPS/IRNSS combined SPP solutions) have an obvious periodic characteristic, which coincides with the satellite orbit repetition period (i.e., a day). Moreover, the epoch-wise ISBs vary within 30 ns for the 7-day datasets, which indicates that the ISB between IRNSS and GPS cannot be ignored. The service rate and ASR of the IRNSS single-system short-baseline RTK positioning are 71.5% and 64.0%, respectively, and those of the GPS single-system case are both close to 100.0%. The mean positioning biases of the IRNSS single-system short-baseline RTK positioning are 5.4, \(-\)21.1, and \(-\)0.2 mm in the three directions, respectively. The accuracy of the GPS-only short-baseline RTK is significantly better than that of the IRNSS-only case, and the corresponding errors decrease to \(-\)0.3, \(-\)0.1, and \(-\)3.4 mm in the three directions, respectively. Compared with the GPS single-system case, the mean positioning biases of the GPS/IRNSS combined short-baseline RTK are comparable and those in the east and up directions are slightly reduced. As to the STD value of the short-baseline RTK positioning errors, the condition is similar to that of the mean positioning biases. The STD statistics of the IRNSS-only solution are 7.8, 19.2, and 29.0 mm in the three directions, respectively, and the corresponding values are reduced by 61.5%, 85.4%, and 68.3%, and 65.4%, 80.7%, and 64.8% for GPS-only and GPS/IRNSS cases, respectively. The RMS values of carrier phase observation residuals derived from GPS/IRNSS combined short-baseline RTK positioning for GPS satellites are 5 mm, and those of IRNSS satellites increase to 12 mm. Conceptualization, L.P. and W.Y. ; methodology, L.P.; software, L.P. and G.P. ; validation, L.P. and G.P. ; formal analysis, G.P. and L.P.; investigation, G.P.