Introduction of new navigation signals L2C (1227.60 MHz) and L5 (1176.45 MHz) to the existing GPS (Global Positioning System) spectrum, under the modernization program of GPS offers the improvement of position accuracy. The present study aims to understand the relative robustness of the L2C and L5 signals compared to legacy L1 C/A signal during periods of scintillations in terms of durations of cycle slips encountered from an anomaly crest location, Calcutta (22.58°N, 88.38°E geographic; magnetic dip 32°N). The data analyzed in this study were recorded during the vernal equinox of 2014 (February–April), a period of high solar activity of cycle 24. Results obtained from the comparative analyses, which are perhaps one of the first from the Indian longitude sector, indicate GPS L5 to be more robust than L1 C/A and L2C in terms of occurrence and duration of cycle slips under adverse ionospheric conditions. Furthermore, loss‐of‐lock events of duration greater than 6 s are found to be more frequent for S4 ≥ 0.6. It is found that frequency sensitivity of the GPS spectrum, in terms of occurrence of cycle slips and loss of locks are in conformity with earlier results from the equatorial region but are different from the high latitudes with respect to local time of occurrence and geomagnetic activity.

Global Navigation Satellite System (GNSS) signals have become a useful tool to analyze signal‐in‐space performance in the presence of ionospheric perturbations with a view to improve the performance of satellite‐based systems and services. For this purpose, continuous monitoring of the signal tracking capabilities of commercial GNSS receivers is a priority, particularly from regions around the crests of Equatorial Ionization Anomaly (EIA), which experiences some of the worst‐case scenarios attributed to ionospheric effects. Ample investigations are reported in literature on GPS signal fading characteristics, while the same for GLONASS and Galileo are limited from Indian low latitude region. The present study aims to report cases of cycle slips and loss‐of‐lock observed independently at GLONASS L1 CA, L2 CA and Galileo L1 BC and E5a, along with a comparative study of robustness of L1 signal in three different constellations GPS, GLONASS, and Galileo, sharing more‐or‐less common ionospheric volume. Data analyzed in this study was recorded during March 2014, a period of high solar activity, from station Calcutta (22.58°N, 88.38°E geographic; magnetic dip 34.54°), located near the northern crest of EIA. Results of this study reveal GLONASS L2 CA to be most affected signal out of all, during periods of ionospheric scintillations. However, when constellations are compared for a particular frequency (L1), Galileo appears to be the least affected. Results of this study could be significant toward better understanding of scintillation effects on GNSS signals while developing more robust applications, especially for a low latitude station.

The ever-increasing dependence on Global Positioning System (GPS) signals for applications based on communication and navigation has put more stringent demands for position determination with highest level of achievable accuracy. Satellite signals are commonly subject to propagation effects introduced by the medium of propagation that result in receiver position errors. One major source of error in the GPS signal results from group delay/carrier phase advance introduced by the Total Electron Content (TEC) present in the ionosphere along the ray path of the signal (Basu et al., 1999;DasGupta et al., 2004). Variation in TEC values could depend on a number of parameters like solar activity (predominant source of variability), local time, season, and geomagnetic conditions (Aarons, 1982;Carrano et al., 2012). In addition, location plays an important role as some of the highest values of TEC are observed in equatorial and low-latitude regions (Aarons, 1982;DasGupta et al., 2006). Therefore, due to the influence of these effects, the positional accuracy of a receiver can be critically compromised, especially in equatorial region (Paul et al., 2017). While arriving at a position solution, stand-alone single frequency receivers rely upon model-based ionospheric error correction, whereas dual-frequency receivers are at advantage of removing the first order ionospheric delay effects, using direct TEC measurement. Therefore, ionospheric effects can be dominant for single-frequency stand-alone GPS receiver and relatively less for dual-frequency receiver and Differential Global Positioning System (DGPS). The ionospheric error budget is measured to reduce from 4 m for single frequency receivers to 1 m for dual-frequency receivers (Spilker et al., 1996). Previous reports by Skone and Shrestha (2002) reveal that the position determined by DGPS was degraded up to 25-30 m, at a location near equatorial anomaly in Brazil, during a high solar activity period of 1999-2000. Positioning error by a single frequency GPS receiver has been reported to be tens of meters during intense scintillation periods in Thailand (Dubey et al., 2006).The ionosphere being a dispersive medium, group delay (carrier phase advance) of a radio signal, is a function of the frequency (f) of operation (

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