Performance Evaluation of the Dual-Frequency Ionospheric Free Combination on BDS-3 Single Point Positioning Accuracy

Abstract

This article analyzes the BDS Phase III (BDS-3) single point positioning (SPP) kinematic mode performance, under seven different dual-frequency ionospheric free combinations (IFC), namely B1C/B2a, B1C/B3I, B1I/B2a, B1I/B2b, B1I/B3I, B2a/B3I, and B2b/B3I, using the observation data of 84 static multi-GNSS experiment (MGEX) stations for 7 days. And the three coordinates are estimated each epoch as white noise. We have derived a detailed SPP model based on timing group delay (TGD) and inter-signal correction (ISC) for IFC. Next, the BDS-3's five signals are assessed in regard to carrier-to-noise density ratio (C/N0) and code multipath (MP), B2b exhibits the best data quality, with an average C/N0 of 44.51 dB-Hz and the code MP value of 22.40 cm. The difference of C/N0 among BDS-3 single frequency signal is not obvious. The average number of satellites for all seven different IFCs is between 8.45 and 8.56, and the average PDOP value is between 2.03 and 2.08. There is not much difference in the number of satellites and PDOP between different IFCs. The root mean square error (RMSE) was used to assess the SPP performance. The sorted order of SPP kinematic performance of dual-frequency IFC, from best to worst, is B1C/B2a, B1C/B3I, B1I/B2a, B1I/B2b, B1I/B3I, B2a/B3I, and B2b/B3I. The results show that the SPP kinematic accuracy of the B1C/B2a dual-frequency IFC in the three directions of north, east, and up (NEU) is 0.70, 0.69, and 1.68 m, respectively, and B2b/B3I IFC is 3.63, 3.72, and 8.49 m, respectively. B1C/B2a has a positioning accuracy ~5 times better than B2b/B3I. If there are multiple IFC, it is recommended to use B1C/B2a in SPP.