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Navigation satellite system plays a major role in finding the position of a user. Similar to GPS, Navigation with Indian Constellation (NavIC) is developed by India to cater the country needs. The NavIC Standard Positioning Service User Receiver (UR) placed at ACS College of Engineering (12.8914° N, 77.4657° E), Bangalore for field trial and data collection. The accuracy of the navigation system is influenced by several kinds of error factors, among which the signal delay influenced by the ionosphere is the greatest error factor. The delay in signal causes error in satellite signal range data and it is called range error. This range error can reduce the accuracy of user position. Hence estimation of range error is very essential. In order to give the appropriate user position, estimation of Total Electron Content (TEC) is vital, which indicates ionospheric error (signal delay). In this paper, VTEC of ionosphere is estimated for the entire day and over a month. The observation data required for estimation of TEC is collected from NavIC SPS receiver located at ACS College of Engineering Station (ACSCES), Bangalore. By using estimated VTEC value, it is possible to correct range error which results in accurate position estimation. NavIC TEC derived using pseudo range at ACSCES is compared with GPS TEC and IRI-2016 TEC which belongs to IISC Station. From the comparison, it is observed that, the maximum NavIC TEC is 43.0552 TECU and maximum GPS TEC is 44.6131 TECU and maximum IRI-2016 TEC is 18.6 TECU. RMSE between GPS and NavIC TEC is 5.486 TECU, correlation coefficient is 0.9748 and average difference is 5.2306 TECU. Similarly, RMSE between NavIC and IRI-2016 TEC is 9.9899 TECU, correlation coefficient is 0.93 and average difference is 9.421 TECU. From the collected data, C/No are plotted for each satellite. From the C/No plots, it is observed that, C/No is good i.e. above 40 dB-Hz. Based on the results, it is evident that, NavIC is suitable for navigational applications in Indian region. [ABSTRACT FROM AUTHOR]

Ionosphere is the upper atmosphere region that contains sufficient number of electrons which disturb the propagation of radio signal travel from navigational satellite to ground/user receiver. Ionospheric delay in range measurement is related to its Total Electron Content (TEC). Ionospheric delay results in range error and degrades the user position accuracy of navigational satellite systems such as Global Positioning System (GPS) and Indian Regional Navigational Satellite System (IRNSS). Hence a suitable TEC prediction model to correct the range delay in single frequency range measurement is necessary. In dual frequency receiver, ionospheric delay is estimated and eliminated using the two range measurements performed at the same time. This paper describes the TEC prediction methodology using Ordinary Kriging based Surrogate Model (OKSM). OKSM is evaluated using the data received and collected from the IRNSS receiver station installed at ACS College of Engineering (ACSCE), Bengaluru (12.8913 °N, 77.4658 °E), India and other International GNSS Service (IGS) network stations. IRNSS TEC data (January 2018) is calculated by using dual frequency (L5 & S) pseudo range method and TEC is smoothed by normal cubic smoothing spline method. IRNSS Vertical TEC (VTEC) is predicted from 16 January 2018 to 26 January 2018 by using previous six days of estimated VTEC values. Similarly, GPS VTEC for IGS station at IISC, Bengaluru is also predicted for same duration to validate the developed OKSM. In order to evaluate the performance of the developed forecasting model for different geographic locations, solar activity conditions and seasons, the VTEC is predicted and analyzed for different latitude regions such as low-latitude PHON station (6.9599 °N, 158.2101 °E), mid-latitude ALGO station (45.9588 °N, −78.0714 °E) and high-latitude NRIL station (69.3618 °N, 88.3597 °E) during different solar activity conditions (Low-2008, Medium-2011 and High-2013 solar activity) and during different seasons (spring, summer, rainy and winter) in the year 2017. From the analysis of OKSM prediction results, it is observed that, RMSE of predicted TEC varies from 0.79 to 3.6 TECU, MAE is 0.4 to 3 TECU and MAPE is within 40% for ionospheric quiet days. VTEC is also predicted during storm days (26 October 2003 to 31 October 2003). To study the performance of the model, VTEC prediction results of OKSM are compared with prediction results from Standard Persistence Model (SPM) and VTEC derived from International Reference Ionosphere (IRI-2016) model. The RMSE of OKSM is 1.9679 TECU, MAE is 1.245 TECU and MAPE is 9%, whereas for SPM, RMSE is 4.8372 TECU, MAE is 3.7496 TECU and MAPE is 36%. Similarly, for IRI-2016 model, RMSE is 7.9 TECU, MAE is 7.1976 TECU and MAPE is 66%. Therefore, TEC predictions by OKSM are better than SPM and IRI-2016. The results show that the OKSM is useful for applications in ionospheric studies. [ABSTRACT FROM AUTHOR]

The Indian Regional Navigation Satellite System (IRNSS) is an indigenously developed satellite navigation system to meet practical needs. The system, comprising a constellation of seven satellites in GEO orbit, has been fully operational since 2018. It is essential to evaluate the performance of the IRNSS continuously for various applications. As a part of ISRO field trial and data collection program an IRNSS Standard Positioning Service User Receiver (UR) placed at ACS College of Engineering (ACSCE), Bangalore, for independent field trial and data collection. The receiver is operational on a 24 × 7 basis. A MATLAB Graphical User Interface has been developed to analyze and plot the data variation of signal strength, elevation angle, visibility of satellites, user position, position error, geometric dilution of precision (GDOP) and find the availability of the number of satellites plotted for every second based on the received data. From the results, it is observed that the signal strength (C/No) is good, i.e. above 40 dBHz, visibility of satellites at receiver location is good. The mean position at user location is found to be X = 1349700 m , Y = 6070902 m , Z = 1413860 m and latitude of 12.8914 degree, longitude of 77.465 degree and altitude of 739 m. The mean position from IRNSS is compared with Google map results showing a good match. The geometry distance of receiver location with respect to Earth center is estimated and observed. The RMS of position error for L1, L5 and dual frequency (L5+S) at ACSCE, Bangalore, is 9.7444 m, 6.6873 m and 5.6667 m, respectively. Hence, as expected the dual-frequency (L5+S) receiver gives an accurate position rather than the single-frequency signals. The IRNSS TEC is measured using Ionospheric group delay and the pseudo-range of L5 and S band which is collected from ACSCE receiver. A third order Savitzky-Golay-Filtered technique is used for TEC smoothing. RMSE between IRNSS TEC from pseudo-range and GPS TEC is 0.6482 TECU and the correlation coefficient is 0.9981. RMSE between IRNSS TEC from ionospheric delay of L5/S and GPS TEC is 1.971 TECU and the correlation coefficient is 0.9966. Finally, smoothed TEC values derived from pseudo-range measurements give a good result and can be used to generate daily TEC maps. In order to analyze the performance of IRNSS over the Indian region, we have chosen three other receiver stations located at Osmania University (Hyderabad), University of Burdwan (Bardhaman, West Bengal) and Shri Mata Vaishno Devi University (Katra, Jammu and Kashmir). Based on the results, we conclude that the IRNSS constellation is performing well and providing good signals for accurate user position determination and ionospheric data analysis. [ABSTRACT FROM AUTHOR]

Total Electron Content (TEC) is used for calculation of Ionospheric delay. The Precise forecast of TEC is useful to correct the range measurements. TEC depends on the time of measurement, solar radiation (SSN & F10.7), geomagnetic index (AP & KP), season and geographic location of the user. In this paper, Cokriging geostatistical method is applied to build the Surrogate Model (COKSM) to estimate the range error based on predicted Vertical Total Electron Content (VTEC). The model is tested with pseudo-range measurements of L5 & S band data received from the operational NavIC/GPS receiver positioned at ACSCE, Bangalore, India and also using L1& L2 data of IGS network station. In order to assess the developed model, we have predicted and analyzed the ACSCE-NavIC TEC and IISC-GPS TEC and found that COKSM has predicted well for both NavIC (ACSCE) and GPS (IISC) TEC. The average RMSE of COKSM for NavIC TEC prediction is 1.4920 TECU, mean accuracy is 1.1151 TECU and average correlation coefficient is 0.9854. For GPS TEC prediction COKSM yields average RMSE of 1.1435 TECU, mean accuracy as 0.9080 TECU and average correlation coefficient of 0.9926. The average range error of NavIC and GPS are 0.2126 and 0.0938 meters. In order to estimate the performance of COKSM, it is compared with the Median model, Fourier series, NTCM-GL, SPM, LSTM and TIEGM/WEIMER models. Based on the comparison results it is observed that COKSM predicts well than other prediction models and provides the RMSE of 2.1480 TECU, correlation coefficient as 0.9810 and mean accuracy of 1.4044 TECU, also COKSM performs 4.6% better than Median model, 26.10% better than Fourier series model, 56.44% better than NTCM-GL, 56% superior than SPM model and 4.43% better than LSTM model. Apart from this, COKSM performance is assessed by comparing the forecasting results with TIEGM/WEIMER model during the St. Patrick's storm and found that the average range error of COKSM is 1.65 m and TIEGM/Weimer model yields 2.06 m during the chosen period. These results indicate that COKSM gives better prediction results than other models and suitable for navigation applications. [ABSTRACT FROM AUTHOR]