Case Study: Performance Observation of NavIC Ionodelay and Positioning Accuracy
TL;DR: After correcting the ionosphere, troposphere, clock, and other deviations, the average ∼70% NavIC positioning accuracy is improved for the overall observed duration, conditions, and locations.
Abstract: The NavIC is an Indian satellite based navigation system uses the L5 and S-band signals to provide 10 m (metres) and 0.1 m positioning accuracy services for civilian and military users respectively...
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TL;DR: In this paper, the role of ionospheric determinants, such as TEC and scintillation S4, on the accuracy of augmented navigation over low latitude region using a dual-frequency NAVigation with Indian Constellation (NavIC) receiver installed at BITS-Pilani K.K. Birla Goa Campus (Geog. Lat. 15.39 ° N, Geog. Long.
11 citations
TL;DR: GNSS provides precise Position, Velocity, and Timing (PVT) information and various types of receivers of varying cost and complexity are used for collection and collection.
Abstract: Global Navigation Satellite System (GNSS) provides precise Position, Velocity, and Timing (PVT) information. Various types of receivers of varying cost and complexity are used for collection and us...
7 citations
TL;DR: In this paper, the authors investigated the occurrence of tracking failure and effects on the positional accuracy of the NavIC L5-band and S-band system under direct exposure of X2.2 and X9.3 solar flares.
Abstract: The solar flares and geomagnetic storms are considered a potential threat for the upcoming Indian Regional Navigation Satellite System or Navigation with Indian Constellation (NavIC). Therefore, we investigated in detail the occurrence of tracking failure and effects on the positional accuracy of the NavIC L5-band and S-band system under direct exposure of X2.2 and X9.3 solar flare on September 6, 2017, X9.3 is the strongest event since the NavIC signals are in the service. The regional NavIC data (5–6 September 2017) from the equatorial region Trivandrum station and the Equatorial Ionization Anomaly area in India (Surat, Bombay, Hyderabad and Gandhinagar stations), are collected using the accord NavIC dual-frequency (L5-band and S-band) receivers. We have shown that the 1G NavIC signals remain in loss of lock condition for 1 h on September 6, 2017 (X2.2 and X9.3 solar flares), and as a result, positioning accuracy deviated on September 6, 2017. Hence, the solar flare event considered a potential threat for future NavIC based autonomous navigation technologies.
5 citations
DOI•
01 Jan 2021
TL;DR: For enhancing the position accuracy over low latitude Indian sub-continent, satellite-receiver geometry is investigated using weighted least squares-based Dilution of Precision (WGDoP) algorithm using GPS and NavIC combined constellation over Hyderabad region.
Abstract: Positioning accuracy of any navigation system plays a vital role in precise positioning applications like CAT-1 aircraft landings, surveying, etc. GNSS positioning accuracy can be affected by many factors like multipath, refraction in atmospheric layers, and satellite-receiver geometry. As Geometric Dilution of Precision (GDoP) is a dimensionless unit, which characterizes the geometry of satellite-receiver. For enhancing the position accuracy over low latitude Indian sub-continent, satellite-receiver geometry is investigated using weighted least squares-based Dilution of Precision (WGDoP) algorithm using GPS and NavIC combined constellation over Hyderabad region. The results are validated with IGS data of the receiver located at Navigation and Communication Research Centre (NCRC), Chaitanya Bharathi Institute of Technology (CBIT), Hyderabad.
5 citations
DOI•
05 Aug 2021
TL;DR: In this paper, the effect of artificial or natural error sources on satellite signals depends on their location, traveling path and traveling path, and the performance analysis of NavlC signals has been evaluated in terms of Power Spectral Density, acquisition and post-processing parameters like C / No, elevation angle, pseudoranges, ionospheric delay and troposphere delay concerning the location of NavIC receiver at low latitude SVNIT, Surat Station.
Abstract: The navigation and positioning system is vital in both civil and military applications. It has become an integral part of our day-to-day life. Navigation with Indian Constellation (NavIC) is the latest addition in the area of satellite-based navigation systems. To achieve the required positioning accuracy of any satellite-based navigation system, the performance accuracy of an individual satellite is more important. The effect of artificial or natural error sources on satellite signals depends on their location, traveling path. In this paper, the NavlC L5-band and S-band signals are considered. The digital IF data is used, which is logged from NavIC receiver, and the performance analysis of NavlC signals has been evaluated in terms of Power Spectral Density, acquisition and post-processing parameters like C / No, elevation angle, pseudoranges, ionospheric delay and troposphere delay concerning the location of NavIC receiver at low latitude SVNIT, Surat Station (21 °9'50.04” N, 72° 47’1.26” E). This kind of analysis can be useful for future applications of the NavlC.
2 citations
References
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TL;DR: The algorithm designed for this purpose, and implemented in the GPS satellites, requires only eight coefficients sent as part of the satellite message, and contains numerous approximations designed to reduce user computational requirements, yet preserves the essential elements required to obtaingroup delay values along multiple satellite viewing directions.
Abstract: The goal in designing an ionospheric time-delay correctionalgorithm for the single-frequency global positioning system userwas to include the main features of the complex behavior of theionosphere, yet require a minimum of coefficients and usercomputational time, while still yielding an rms correction of at least50 percent. The algorithm designed for this purpose, andimplemented in the GPS satellites, requires only eight coefficientssent as part of the satellite message, contains numerousapproximations designed to reduce user computationalrequirements, yet preserves the essential elements required to obtaingroup delay values along multiple satellite viewing directions.
1,181 citations
TL;DR: In this paper, it was shown that at any point in a dry atmosphere, the atmospheric refractivity depends on both pressure and temperature (the ratio P/T), not of temperature.
Abstract: Knowledge of the height integral of atmospheric refractivity (n — 1), where n is the refractive index, is essential for prediction of atmospheric range effect at any elevation angle. Observed values of the height integral for the lower, nonionized atmosphere can be obtained from weather balloon ascent data. Year-long collections of data from widely separated locations were used to relate this integral to surface data. Although (n — 1) at any point in a dry atmosphere depends on both pressure and temperature (the ratio P/T), the height integral of the observed dry part of (n — 1) is a linear function of surface pressure only, not of temperature. This is theoretically correct since P/T is equivalent to density, and the integral of density with height yields surface pressure. By application of this finding, the equivalent height for a (theoretically justified) quartic (n — 1) model (dry part) should be found to vary directly as surface temperature; the value obtained (least-squares fit to observed data) is 40.1 km for surface T = 0°C with a height expansion coefficient of 0.149 km per surface degree C. This would reduce the equivalent height to zero near 0° Kelvin. This theoretical model matches observed height integrals with an rms error of a few millimeters out of 2.3 meters (far less than 1%). Agreement between stations is excellent. A study of the more variable but much smaller wet part is in progress. The wet part is significant at radio but not at optical frequencies.
273 citations
"Case Study: Performance Observation..." refers methods in this paper
...78° E) station data of the first week of September 2016, 2017 and 2018 is compared after correcting the satellite clock correction, ionospheric and tropospheric delays by the dual-frequency method [1–4] and the Hopfield model [17]....
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Jiuhou Lei1, Fuqing Huang1, Xuetao Chen1, Jiahao Zhong1, Dexin Ren1, Wenbin Wang2, Xinan Yue3, Xiaoli Luan1, Mingjiao Jia1, Xiankang Dou1, Lianhuan Hu3, Baiqi Ning3, Charles Owolabi1, Jinsong Chen, Guozhu Li3, Xianghui Xue1 •
91 citations
TL;DR: In this article, a modified planar fit model is applied for GPS aided geo augmented navigation (GAGAN) data on similar lines as was done for WAAS and the results are encouraging.
Abstract: Several countries have been developing satellite-based augmentation systems (SBAS) for improving positional accuracy of global positioning system (GPS). India is also developing one such system popularly known as GPS aided geo augmented navigation (GAGAN) system. Modelling of ionospheric effects is one of the major challenges in developing precise and reliable GAGAN. The high values of total electron content (TEC), the large diurnal and seasonal variability and intense irregularities present in the low-latitude ionosphere, lead to unacceptable positional errors in GAGAN service region. Todd Walter et al. of Stanford University, USA have made significant contribution in the area of SBAS ionospheric grid modelling by developing the popularly known planar fit model. It is reported by Walter et al. (2000) that a constant decorrelation value of 35 cm was proposed over the wide area augmentation system (WAAS) service region. To provide accurate estimation of ionospheric delays at user ionospheric pierce points (IPP) during a storm or intense irregularities, an irregularity detector and a decorrelation adaptor are incorporated in the modelling. As planar fit model is not adequate to model intense irregularities of Indian ionosphere, a modified planar fit model is applied for GAGAN data on similar lines as was done for WAAS and the results are encouraging.
50 citations
"Case Study: Performance Observation..." refers methods in this paper
...GAGAN for the low latitude Indian subcontinent is mitigated based on different regional grid models such as MinimumMean Square Error [11], Kriging, Inverse Distance Weighted (IDW) with the Klobuchar model and planar fit model [12]....
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01 Oct 2007
TL;DR: In this article, a near real-time grid-based ionospheric delay model for correcting propagation delay at 1575.42 MHz and 1227.6 MHz was proposed to meet the requirement of correction with 0.5 m maximum residue over Indian region.
Abstract: Satellite Based Augmentation System (SBAS), being developed by Indian Space Research Organization (ISRO) in collaboration with Airports Authority of India (AAI) is known as “GPS Aided GEO Augmented Navigation” (GAGAN). It is expected to offer better accuracy and integrity of navigation service than with GPS alone by providing correction terms to the GPS signals. This is achieved by modelling a Near Real Time Grid Based Ionospheric Delay Model for correcting propagation delay at 1575.42 MHz (L1) using measurements at 1575.42 and 1227.6 MHz (L2). Existing algorithms are replaced by Kriging based model to meet the requirement of correction with 0.5 m maximum residue over Indian region. Details of the data collection and pre-processing, including estimation of the Total Electron Content (TEC), which is a measure of ionospheric delay, has been described. Kriging algorithm and some preliminary results of studies are also presented in this paper. This includes the spatial decorrelation of the stochastic random field over the deterministic variation of ionospheric TEC. Its variation with time and locations are investigated and a temporal dependence found to exist. Large scale ionospheric irregularities and depletions that cause severe amplitude and phase scintillations are also studied. Their impacts on GAGAN are also shown. Some major scientific studies required to be carried out over Indian region to improve the GAGAN performance is discussed.
37 citations