# Assessment of IRNSS-Only Data Processing: Availability, Single-Frequency SPP and Short-Baseline RTK
## 5 Results and Analysis
### Performance of Short-Baseline RTK Positioning  
Due to the limited number of available IRNSS satellites and the unstable tracking of IRNSS satellites by the MGEX stations, it is difficult to perform the IRNSS-only long-baseline precise relative positioning. In this section, the performance of the IRNSS single-system short-baseline RTK positioning is assessed based on the datasets from the two stations YARR and YAR3 spanning seven consecutive days from 7-13 July 2019. The length of the short baseline is approximately 20 m. For comparative analysis, the results of the GPS-only and GPS/IRNSS cases are also provided. In the short-baseline RTK, only GPS L1 and IRNSS L5 signals are used. Reference baseline values are obtained in static relative positioning based on the seven-day datasets. Figure 15 illustrates the epoch-wise position errors of the ambiguity-fixed solutions for IRNSS-only, GPS-only, and GPS/IRNSS short-baseline RTK on 7 July 2019. The epoch-wise position errors of IRNSS-only cases are less than 5 cm in the horizontal direction and 10 cm in the vertical direction, while those of both GPS-only and GPS/IRNSS cases are smaller than 1 cm in the horizontal direction and 3 cm in the vertical direction. The RTK solutions of GPS-only and GPS/IRNSS cases are comparable in the three directions. We further analyze the service rate, ASR, mean positioning bias, and STD value of the positioning error for the single-day short-baseline RTK results under the three system combination cases. When the ratio-test value is larger than three, the ambiguity is considered to be successfully fixed. The service rate refers to the percentage of the number of epochs, at which the position solutions (including both ambiguity-float and ambiguity-fixed solutions) can be achieved over the total epochs. The ASR is taken as the percentage of the number of epochs with successfully fixed ambiguities over that with available ambiguity-float or ambiguity-fixed position solutions. Table 4 shows the 7-day  
Figure 15: Epoch-wise position errors of the ambiguity-fixed solutions for IRNSS-only, GPS-only, and GPS/IRNSS short-baseline RTK on 7 July 2019.  
average results of these statistical values. The service rate of the IRNSS-only case is 71.5%, and that of the other two cases reaches 100.0%. In addition, the ASR of the IRNSS-only case is only 64.0%, and that of the other two cases reaches nearly 100.0% (specifically 99.5% for GPS and 99.9% for GPS/IRNSS). Regarding the mean positioning biases, they are at the centimeter level for the IRNSS-only case, which are 5.4, \(-\)21.1, and \(-\)0.2 mm in the east, north, and up directions, respectively. The GPS-only case has significantly smaller mean positioning biases than the IRNSS-only case, which are reduced to \(-\)0.3, \(-\)0.1, and \(-\)3.4 mm in the three directions, respectively. The introduction of IRNSS observations slightly pollutes the accurate GPS-only results perhaps due to the severe multipath-like interferences as shown in the IRNSS-derived coordinates (see Figure 15). Regarding the STD value of positioning errors, it is 7.8, 19.2, and 29.0 mm for the IRNSS-only case in the three directions, respectively, whereas that of the GPS-only case is much better, which is reduced by 61.5%, 85.4%, and 68.3% to 3.0, 2.8, and 9.2 mm in the three directions, respectively. The GPS/IRNSS integration slightly increases the STD error in the north and up directions compared with the GPS-only case, while the corresponding reduction in STD error can be 65.4%, 80.7%, and 64.8% in the three directions compared with the IRNSS-only case, respectively. Compared to the single-frequency short-baseline RTK positioning performance of BDS-3 that also covers Asian areas (e.g., [24], with RMS positioning errors of 3-8 mm in the horizontal directions and 9-19 mm in the vertical direction, and ASR of higher than 91%), that of IRNSS is obviously worse (with RMS positioning errors of 9.5/28.5/29.0 mm in the three directions, and ASR of 64%).