Evaluation of Ionospheric Delay Effects on Multi-GNSS Positioning Performance

Abstract

Ionospheric delay is a significant error source in multi-GNSS positioning. We present different processing strategies to fully exploit the ionospheric delay effects on multi-frequency and multi-GNSS positioning performance, including standard point positioning (SPP) and precise point positioning (PPP) scenarios. Datasets collected from 10 stations over thirty consecutive days provided by multi-GNSS experiment (MGEX) stations were used for single-frequency SPP/PPP and dual-frequency PPP tests with quad-constellation signals. The experimental results show that for single-frequency SPP, the Global Ionosphere Maps (GIMs) correction achieves the best accuracy, and the accuracy of the Neustrelitz TEC model (NTCM) solution is better than that of the broadcast ionospheric model (BIM) in the E and U components. Eliminating ionospheric parameters by observation combination is equivalent to estimating the parameters in PPP. Compared with the single-frequency uncombined (UC) approach, the average convergence time of PPP with the external ionospheric models is reduced. The improvement in BIM-, NTCM- and GIM-constrained quad-constellation L2 single-frequency PPP was 15.2%, 24.8% and 28.6%, respectively. The improvement in convergence time of dual-frequency PPP with ionospheric models was different for different constellations and the GLONASS-only solution showed the least improvement. The improvement in the convergence time of BIM-, NTCM- and GIM-constrained quad-constellation L1/L2 dual-frequency PPP was 5.2%, 6.2% and 8.5%, respectively, compared with the UC solution. The positioning accuracy of PPP is slightly better with the ionosphere constraint and the performance of the GIM-constrained PPP is the best. The combination of multi-GNSS can effectively improve the positioning performance.

Estimation of GPS Differential Code Biases Based on Independent Reference Station and Recursive Filter

“…Recently, a number of algorithms for GNSS DCB estimates based on multi-frequency measurements have been proposed [7][8][9]. Apart from the commonly adopted method by setting the DCB as a constant during the GNSS TEC estimation [10][11][12][13][14][15], some other algorithms are proposed to decrease the computation costs by utilizing global ionospheric maps [4]. Furthermore, various optimization methods have been proposed for faster DCB determination and more accurate ionospheric modeling, such as optimization on DCB estimation based on regional or single station ionospheric modeling [16][17][18][19][20][21][22][23][24][25][26][27][28][29].…”

“…Nowadays, Global Navigation Satellite Systems (GNSS) observations provide various ways to estimate geophysical parameters, and one of the most important parameters is the total electron content (TEC) measurements for Earth's ionosphere research [1][2][3][4][5][6]. Due to the frequency dispersive property of the ionosphere, the ionospheric delay experienced by electromagnetic signals can be estimated by dual-frequency measurements.…”

Performance of Selected Ionospheric Models in Multi-Global Navigation Satellite System Single-Frequency Positioning over China

“…In addition, the GLONASS pseudo-range inter-frequency biases (IFBs) should be estimated for each GLONASS frequency in PPP since the GLONASS adopts frequency division multiple access (FDMA) technique to distinguish the signals from different satellites [18,19]. Therefore, the multi-GNSS GRAPHIC model can be presented as follows [20,21]:…”

“…In the ionosphere-constrained SF-PPP model, the ionospheric delay regarded as an unknown parameter can be estimated by adding the pseudo-ionospheric observations from the empirical model with constraints. The undifferenced and uncombined pseudo-range and carrier phase observations with one satellite can be written as [17,20]:…”

“…t is the corresponding local time at IPP in hours. Since the precision of the GIM model is approximately 2-8 TECU, the variance of the zenith ionospheric delay σ 2 ion,0 and σ 2 ion,1 are set as 0.09 m 2 and 0.09 m 2 , respectively [20]. Similarly, the Grid as a regional ionospheric model has an accuracy of 0.5 m in zenith direction, hence both σ 2 ion,0 and σ 2 ion,1 are set as 0.25 m 2 .…”