L1 Signals Research Articles

GNSS Signal Distortion Estimation: A Comparative Analysis of L5 Signal from GPS II and GPS III

The nonlinear navigation payload transmission channel introduces errors at a system level, resulting in a distortion of the received signal and affecting differential positioning users. This work models the transmission channel of the navigation payload and uses the joint estimation algorithm to calculate the digital distortion and analog channel response of the transmission channel from the received signal. On the above basis, the algorithm and model are verified by GPS-L5 measured data, and the channel characteristics of GPS II and GPS III are deeply analyzed. The results show that the existing GPS IIF satellites have a digital distortion, which is negligible in GPS III satellites. Regarding the analog channel response, GPS III has better amplitude and group delay consistency than GPS II. Lastly, the ranging bias caused by the transmission channel of the navigation payload is provided to the user for reference, and GPS III is improved by approximately 0.02 m compared with GPS II. This study provides support for adjusting the satellite signal pre-distortion and enriches subsequent GNSS signal quality assessment work; it can also be used as a reference for differential positioning users.

Double difference method with zero and short base length carrier phase measurements for Navigation with Indian Constellation satellites L5 (1176.45 MHz) signal quality analysis

SummaryThe carrier phase (CP) measurements should be unambiguous to achieve the enhanced accuracy of Global Navigation Satellite System (GNSS) services. However, all the real‐time CP measurements are manipulated by different errors, namely, satellite and receiver clock error, ionosphere delay, troposphere delay, integer ambiguity, etc. Even after removing or minimizing all these errors, the CP measurements are influenced by multipath error and receiver hardware residual or bias. In this research article, a double difference (DD) method is proposed to estimate residual or bias in CP observations of Navigation with Indian Constellation (NavIC). The proposed method abolishes all the common errors and provides bias. However, the CP measurement with a bit of bias value can be considered a high‐quality signal. Here, we investigate the quality of NavIC satellites L5 (1176.45 MHz) signal with real‐time measurements obtained through zero base length (ZBL) and short base length (SBL) experiments conducted at Kurnool (15.79°N, 78.07°E), India. The results show that the CP measurement bias of the L5 signal is within the range ±0.338 and ±1.688 m, respectively, for stationary and moving receivers. The bias was enhanced to 3.71 m for the SBL measurements. The results also demonstrate that the bias is low when carrier to noise (C/No) is high, and its range is nearly the same for all the days. This research would be helpful to estimate the bias that improves accuracy of precise point positioning (PPP) applications.

Carrier-Aided Dual-Frequency Vectorized Tracking Architecture for NavIC Signals

A new carrier-aided dual-frequency vectorized tracking (CA-DFVT) architecture for the Navigation with Indian Constellation (NavIC) is presented. CA-DFVT tracks both NavIC L5 (1176.45 MHz) and S-band (2492.028 MHz) signals concurrently. It uses the precise carrier phase measurements from the S-band signal and the unambiguous code phase measurements from the L5 signal to form a new measurement model for the extended Kalman filter (EKF) to estimate the position, velocity, and time (PVT) solutions. The new measurement model takes advantage of the benefits of the higher frequency S-band signal, i.e., less ionospheric delay and carrier phase noise, as well as the L5 signal’s inherent noise mitigation capabilities. Compared to the single-frequency approach, the dual-frequency approach in CA-DFVT eliminates the ionospheric effect and minimizes other errors, resulting in better navigation solutions. The proposed CA-DFVT enhances the reliability and robustness of NavIC signal tracking and position estimation in interference and high dynamics environments. We used static and dynamic field tests to validate the performance and robustness of the proposed CA-DFVT receiver architecture. In comparison to single-frequency (L5/S-band) vector tracking, the CA-DFVT receiver demonstrated consistent signal tracking and position estimation with higher position accuracy. In the static case, the mean horizontal position accuracy of CA-DFVT improves by approximately 2–4 and 9–14 m compared to L5-only VT and S-only VT, respectively, while, in the dynamic case, it improves by approximately 2–5 and 25–42 m, respectively.

Soil Moisture Estimation Based on GNSS-R Using L5 Signals From a Quasi-Zenith Satellite System

Soil Moisture Estimation Based on GNSS-R Using L5 Signals From a Quasi-Zenith Satellite System

Coherent GNSS-Reflections Characterization Over Ocean and Sea Ice Based on Spire Global CubeSat Data

This article assesses the coherency of Global Navigation Satellite System (GNSS) signals reflected off the oceans and sea ice under grazing angle geometries and received aboard low Earth orbit (LEO) CubeSats for precision altimetry applications. The coherency is characterized as a function of ocean surface conditions and reflected signal parameters based on Spire Global CubeSat data collected from January to April 2019. The data contain 50-Hz GPS L1 and L2 carrier phase estimations obtained by open-loop tracking. Indicators based on the circular statistics of the excess-phase noise are developed to identify coherent and semicoherent reflections. Based on these indicators, we found that ~1% and 44% of GPS reflections over the ocean and sea ice, respectively, have potential for precision altimetry. The coherent and semicoherent reflection rates reach 23% in areas less than 200 km from the coastline and under calm sea conditions. Over young sea ice over the Arctic, this rate can be as high as 70%. There is a strong relationship between coherency and signal strength, and the coherency occurrence rate improves as the grazing angle decreases. The quality of the L1 and L2 coherent reflections is similar over sea ice, while, for reflections over the ocean, L1 signals are predominantly noisier and less coherent than the L2 signals. Using a postprocessing filtering method, the semicoherent reflections can achieve a similar level of altimetry precision as that of the coherent ones, thereby increasing the along-track length of the retrieved altimetry profile.

Assessment of GPS positioning performance using different signals in the context of ionospheric scintillation: a month-long case study on São José dos Campos, Brazil

The ionospheric scintillation associated to small-scale irregularities in the ionospheric layer can lead to performance degradation of Global Navigation Satellite Systems (GNSS) signals, and the reduction of positioning accuracy. The influence of the ionospheric layer on the GNSS systems is expected to be different for each signal since it is transmitted on different carrier frequencies. This paper presents the results of a quantitative analysis of the scintillation amplitude of GPS (Global Positioning System) signals at L1, L2 and L5 frequencies, aiming to evaluate the impact of the ionospheric scintillation effects on the GPS frequencies. As the ionospheric scintillation may impact positioning accuracy, we also present an assessment of GPS point positioning using those frequencies. The GPS sample data were collected for 30 days between November and December 2014 at SJCE station located in São José dos Campos (SP), Brazil. Such a region is subjected to the equatorial anomaly effects being characterized by the occurrence of strong ionosphere scintillation. Considering the quantitative analysis, during the different levels of ionospheric scintillation presented a similar behavior, the magnitude of scintillations is small for the L1 signal and larger for L5. In general, the results confirmed that lower frequencies (L2 and L5) suffer more impact from intense scintillation than L1. Regarding the positioning assessment, the multi-frequency positioning was more accurate than single frequency. Considering dual-frequency positioning, results with L1-L2 were more accurate than those with L1-L5 signals. With single-frequency positioning, the L1 signal was more accurate compared to the L2 frequency.

Analysis and Mitigation of Crosstalk Effect on Coastal GNSS-R Code-Level Altimetry Using L5 Signals from QZSS GEO

Coastal Global Navigation Satellite System Reflectometry (GNSS-R) can be used as a valuable supplement for conventional tide gauges, which can be applied for marine environment monitoring and disaster warning. Incidentally, an important problem in dual-antenna GNSS-R altimetry is the crosstalk effect, which means that the direct signal leaks into the down-looking antenna dedicated to the reflected signals. When the path delay between the direct and reflected signals is less than one chip length, the delay waveform of the reflected signal is distorted, and the code-level altimetry precision decreases consequently. To solve this problem, the author deduced the influence of signal crosstalk on the reflected signal structure as the same as the multipath effect. Then, a simulation and a coastal experiment are performed to analyze the crosstalk effect on code delay measurements. The L5 signal transmitted by the Quasi-Zenith Satellite System (QZSS) from a geosynchronous equatorial orbit (GEO) satellite is used to avoid the signal power variations with the elevation, so that high-precision GNSS-R code altimetry measurements are achieved in the experiment. Theoretically and experimentally, we found there exists a bias in proportion to the power of the crosstalk signals and a high-frequency term related to the phase delay between the direct and reflected signals. After weakening the crosstalk by correcting the delay waveform, the results show that the RMSE between 23-h sea level height (SSH) measurements and the in-situ observations is about 9.5 cm.

Chronic Lymphocytic Leukemia, T-Cell Large Granular Lymphocytic Leukemia in a Pediatric Patient without Underlying Condition

BackgroundLarge granular lymphocytic (LGL) leukemia is a rare hematological malignancy in children. The two types of LGL leukemia that have been described are T-cell and Natural Killer cell leukemia. It is most commonly diagnosed in older adults, average age of 60-year-old. About 20 cases of LGL leukemia have been reported in children and young adults. All the patients in the reported cases had immune dysregulation conditions, such as chronic graft versus host disease, common variable immunodeficiency disorder, Crohn's disease and autoimmune hemolytic anemia. Here we report a case of T-cell LGL leukemia in a 11-year-old boy without underlying condition who presented with chronic neutropenia associated with gingival hypertrophy, recurrent skin abscesses, aphthous ulcers, clubbing of nails and low bone density.MethodsMulti-institution collaboration and literature review.Case Description11-year-old male with two years history of episodic gum bleeding with gingival hypertrophy, skin abscesses, aphthous ulcers, chronic neutropenia and lymphocytosis presented to our clinic for further evaluation. Initial workup demonstrated moderate to severe neutropenia (absolute neutrophil count between 400/ul to 800/ul) with low segmented neutrophils of 2-4% and high lymphocytes of more than 80%, but normal white blood cell count, hemoglobin for age and platelet count. Peripheral blood smear showed several variant lymphocytes with cytoplasmic blebs and no immature cells present. Expansion of T-cell large granular lymphocytes were detected in peripheral blood by flow cytometry. Due to new symptom of lower back pain, a lumbar Magnetic Resonance Imaging was performed. Results showed low bone density with mild compression deformity of L1 and abnormal heterogeneous marrow signal with heterogeneous contrast enhancement. The abnormal bone marrow signal promoted the investigation of bone marrow aspiration and biopsy. Flow cytometry detected forty-five percent of lymphocytes with immuno-phenotype of CD3+, CD8+, CD57+, CD16+, CD7+ and CD5-. The morphology of minimal cytoplasm and mature chromatin along with immunophenotype were consistent with clonal T-cell large granular lymphocytic proliferation/leukemia. Further cytogenetic tests showed TCR gamma and beta genes rearrangement, STAT3 N647I mutation with normal male karyotype. A peripheral blood congenital neutropenia panel, which included a total of 18 genes, found a heterozygous mutation c 279 G>A in the Gata2 gene; a variant of uncertain significance. Next generation sequencing showed somatic mutations of TRGV10, TRGV8 TRGJ1, TNFAIP3 and STAT3. However, there was no germline mutations detected in sample from skin biopsy. Comprehensive evaluation by immunology, rheumatology and gastroenterology failed to detect any underlying conditions.ConclusionDue to rarity of LGL leukemia in pediatrics, standard of care guidelines are currently unavailable. Extrapolated from limited literature, two management options are considered: watch and wait approach versus early initiation of immunosuppressant chemotherapy. Improved diagnostics can aide management strategies in this patient population. DisclosuresNo relevant conflicts of interest to declare.

Estimating the Fractional Cycle Biases for GPS Triple-Frequency Precise Point Positioning with Ambiguity Resolution Based on IGS Ultra-Rapid Predicted Orbits

We investigate the estimation of the fractional cycle biases (FCBs) for GPS triple-frequency uncombined precise point positioning (PPP) with ambiguity resolution (AR) based on the IGS ultra-rapid predicted (IGU) orbits. The impact of the IGU orbit errors on the performance of GPS triple-frequency PPP AR is also assessed. The extra-wide-lane (EWL), wide-lane (WL) and narrow-lane (NL) FCBs are generated with the single difference (SD) between satellites model using the global reference stations based on the IGU orbits. For comparison purposes, the EWL, WL and NL FCBs based on the IGS final precise (IGF) orbits are estimated. Each of the EWL, WL and NL FCBs based on IGF and IGU orbits are converted to the uncombined FCBs to implement the static and kinematic triple-frequency PPP AR. Due to the short wavelengths of NL ambiguities, the IGU orbit errors significantly impact the precision and stability of NL FCBs. An average STD of 0.033 cycles is achieved for the NL FCBs based on IGF orbits, while the value of the NL FCBs based on IGU orbits is 0.133 cycles. In contrast, the EWL and WL FCBs generated based on IGU orbits have comparable precision and stability to those generated based on IGF orbits. The use of IGU orbits results in an increased time-to-first-fix (TTFF) and lower fixing rates compared to the use of IGF orbits. Average TTFFs of 23.3 min (static) and 31.1 min (kinematic) and fixing rates of 98.1% (static) and 97.4% (kinematic) are achieved for the triple-frequency PPP AR based on IGF orbits. The average TTFFs increase to 27.0 min (static) and 37.9 min (kinematic) with fixing rates of 97.0% (static) and 96.3% (kinematic) based on the IGU orbits. The convergence times and positioning accuracy of PPP and PPP AR based on IGU orbits are slightly worse than those based on IGF orbits. Additionally, limited by the number of satellites transmitting three frequency signals, the introduction of the third frequency, L5, has a marginal impact on the performance of PPP and PPP AR. The GPS triple-frequency PPP AR performance is expected to improve with the deployment of new-generation satellites capable of transmitting the L5 signal.

Evaluation and Correction of Elevation Angle Influence for Coastal GNSS-R Ocean Altimetry

The elevation angle influence on coastal GNSS-R ocean code-based altimetry for GPS signals (L1 C/A and L5) and BDS B1 signals is investigated, and the corresponding correction method is presented. The study first focuses on the coastal ocean altimetry method, including the general experiment geometry and the code delay estimation using the single-point tracking algorithm. The peak power and the maximum first derivative are used as the location of the specular point. Then, the sensitivity of the height retrieved using the above coastal ocean altimetry method to elevation angle is analyzed based on the Z-V model. It can be seen that the elevation angle has a significant influence on the height retrieval, which will affect the precision of the coastal GNSS-R ocean altimetry. Finally, two correction methods, the model-driven method and the data-driven method, are proposed. The coastal altimetry experiments demonstrate that the correction methods can correct the elevation angle influence, and the data-driven method is more effective. The experimental results show that, after correcting the elevation angle influence, the code-based altimetry precision of the GPS L1 C/A signal, L5 signal, and BDS B1 signal can be up to the meter level, decimeter level (less than 4 decimeters), and meter level with respect to a reference tide gauge (TG) data set, respectively, without smoothing over time. These results provide information to guide the sea surface height retrieval using coastal GNSS-R, especially multi-satellite observation and GNSS signal with a higher chipping rate.

Improving GNSS-R Sea Surface Altimetry Precision Based on the Novel Dual Circularly Polarized Phased Array Antenna Model

Antenna is one of the key payloads of the GNSS-R system, and the gain is an important performance parameter. The signal-to-noise ratio (SNR) of the received signal can be improved by increasing the gain of the GNSS-R antenna, therefore the measurement accuracy is improved. However, the antenna gain and its beam width, these two performance parameters, are contradictory. If the gain of the antenna is increased, its beam width will inevitably become narrower. This narrowed beam width will affect the width of the survey strip for the GNSS-R system, which cannot meet the requirement of the high-precision and high-spatial resolution spaceborne GNSS-R sea surface altimetry in the future. In this paper, a novel dual circularly polarized phased array antenna (NDCPPA) is proposed and investigated. First, the GNSS-R satellites currently operating in orbit are all cGNSS-R systems, which use the traditional element antenna (TEA) method for measurement. The antenna used in this method is with low gain, which limits the improvement of sea surface measurement accuracy. In response to this problem, this paper establishes an NDCPPA model of iGNSS-R measurement system based on the theory of coherent signal processing on the sea surface. This model uses the high-gain scanning beam to increase the gain of the iGNSS-R antenna without affecting its coverage area, thereby improving the sea surface altimetry precision. Second, in order to verify the gain improvement effect brought by adopting the NDCPPA model, an NDCPPA model verification prototype for iGNSS-R sea surface altimetry was designed and fabricated, and then measured in a microwave anechoic chamber. The measurement results show that, compared with the TEA method, the antenna gain of our proposed verification prototype is enhanced by 9.5 dB. And the measured and designed value of the gain of the verification prototype matches well. Third, based on the GPS L1 signal, the NDCPPA model is used to analyze the effect of improving the precision of sea surface altimetry. Compared with the TEA method, the proposed model can increase the altimetric precision of the nadir point from 7.27 m to 0.21 m, which effectively improves the performance of the iGNSS-R altimetry. The NDCPPA model proposed in this article can provide the theoretical method basis and the crucial technical support for the future high-precision and high-spatial-resolution GNSS-R sea surface altimetry verification satellite.

GPS L1 signals absorption in high-latitude lower ionosphere during severe geomagnetic storm in June 2015

Based on the results of an analysis of FORMOSAT-3/COSMIC radio occultation measurements, the absorption of DM-radio waves (wavelength ∼19 cm) in the lower high-latitude ionosphere of the Earth was detected. The maximum absorption value is ∼3 dB in the range from ∼60 to ∼90 km and, in some cases, it reaches ∼10 dB at altitudes from ∼90 to ∼95 km. A method for determining the vertical profiles of the absorption coefficient by solving the inverse problem of radiosonding in the Earth’s lower ionosphere is proposed. The absorption layers, caused by powerful bursts of X-ray radiation and strong changes in geomagnetic conditions during the storm, were reliably identified in individual sessions. It was found that, at altitudes from ∼90 to ∼100 km, the value of the absorption coefficient of DM-radio waves reached values (5.69 ± 1.35)·10−3 dB/km.

A deep fading assessment of the modernized L2C and L5 signals for low-latitude regions

A deep fading assessment of the modernized L2C and L5 signals for low-latitude regions

Determination of sea level variations in Turkish Mediterranean coast using GNSS reflectometry

Global Navigation Satellite System Reflectometry (GNSS-R) can be used to measure sea level heights based on reflected signals recorded as oscillations in signal-to-noise ratio (SNR) data. This study utilizes the SNR data from an existing MERS, located in Erdemli, Mersin on the Mediterranean coast of Turkey over a one-year time period. The dominant multipath frequency in the SNR data is derived with two methods presented in this study: the Lomb-Scargle periodogram (LSP) and the LSP with the Moving Average (MA) filtering. The results of both methods are compared in terms of the accuracy and correlation with respect to sea level records from the nearby Erdemli tide gauge. The correlations between the GNSS-R and tide gauge by using the LSP are 0.88 and 0.84 for GPS L1 and L5 signals, respectively. With the LSP with MA method, the correlations are increased by 0.91 and 0.88 for GPS L1 and L5 signals, respectively.

A gradient descend method‐based none‐line‐of‐sight‐induced code delay searching in global navigation satellite system

In urban areas with narrow streets and tall buildings, none-line-of-sight (NLOS) or multipath (MP) signals severely attenuate the positioning accuracy of the global navigation satellite system (GNSS). vector tracking loop (VT) has been employed in NLOS/MP signal detection and correction; its feasibility and superior performance have been assessed and demonstrated in previous research studies. In VT, the navigation solutions are fed back to calculate the signal tacking parameters and complete the carrier and code tracking. The NLOS/MP reception induces code delay to the code tracking. The generated local signal replicas are mixed with the received signal; the code and carrier discriminators’ outputs are employed as the measurements to estimate the navigation solutions in the VT navigation filter. In order to extract the code delay induced by the NLOS or MP, multiple correlators (MCs) are usually utilised to search for the code delay. However, more correlators will bring much heavier computation load and a real position is necessary for calculating the signal tracking parameters. The strap-down inertial navigation system (SINS) can generate short-term accurate navigation solutions. In this work, a gradient descend (GD) method is designed for extracting the NLOS/MP-induced delay in the correlators’ measurements level. The VT/SINS ultra-tightly coupled navigation system (VT-UTC) is developed to obtain mutual aiding between these individual systems. In VT-UTC, the corrected SINS navigation solutions are employed for calculating the signal tracking parameters, and reliable navigation solutions from the SINS can help to extract the code delays induced by the NLOS. Two field tests with global positioning system L1 signal are carried out for assessing the performance of the GD method in the VT-UTC framework. Comparisons between the MC and GD method show that the correlators’ computation reduces a lot since much fewer correlators are calculated in the code delay searching. Also, reliable navigation solutions from the SINS could help to calculate the signal tracking parameter while in-view GNSS satellites are limited.

On the Properties of and Ionospheric Conditions Associated With a Mid‐Latitude Scintillation Event Observed Over Southern United States

AbstractWhile low and high‐latitude ionospheric scintillation have been extensively reported, significantly less information is available about the properties of and conditions leading to mid‐latitude scintillations. Here, we report and discuss scintillation observations made in the Southern United States (UT Dallas, 32.99°N, 96.76°W, 43.2°N dip latitude) on June 1st, 2013. The measurements were made by a specialized dual‐frequency GPS‐based scintillation monitor which allowed us to determine main properties of this mid‐latitude scintillation event. Additionally, simultaneous airglow observations and ionospheric total electron content (TEC) maps provided insight on the conditions leading to observed scintillations. Moderate amplitude scintillations (S4>∼0.4) occurred in both L1 and L2C signals, and severe (S4 > ∼0.8) events occurred in L2C signals at low (<30°) elevation angles. Phase scintillation accompanied amplitude fadings, with maximum σϕ values exceeding 0.5 radians in L2C. We also show that the observed phase scintillation magnitudes increased with amplitude scintillation severity. Decorrelation times were mostly between 0.25 and 1.25 s, with mean value around 0.65 s for both L1 and L2C. Frequency scaling of S4 matched fairly well the predictions of weak scattering theory but held for observations of moderate and strong amplitude scintillation as well. Scintillation occurred during the main phase of a modest magnetic storm that, nevertheless, prompted an extreme equatorward movement of the mid‐latitude trough and large background TEC enhancements over the US. Scintillations, however, occurred within TEC and airglow depletions observed over Texas. Finally, scintillation properties including severity and rapidity, and associated TEC signatures are comparable to those associated with equatorial spread F.

GLONASS\u2013only FDMA+CDMA RTK: Performance and outlook

An assessment of standalone GLONASS RTK performance is provided using its FDMA and CDMA signals. The new integer-estimable GLONASS FDMA model (Teunissen 2019), which guarantees the integer-estimability of its ambiguities, is employed. We introduce the combined integer-estimable GLONASS FDMA+CDMA model and compare its strength against the FDMA model for instantaneous integer ambiguity resolution and positioning. Various combinations of GLONASS signals are considered including FDMA L1, FDMA+CDMA L1+L3, FDMA L1+L2 and FDMA+CDMA L1+L2+L3. To provide insight into the current RTK performance of GLONASS, we used observations of a short baseline to analyze the integer ambiguity resolution success rate and positioning precision, formally and empirically. To provide insight into the future RTK performance of GLONASS, we present a formal analysis of the integer ambiguity resolution success rate and ADOP, assuming that all the GLONASS satellites transmit FDMA L1, L2 and CDMA L3 signals. A formal analysis of standalone GLONASS ambiguity resolution based on current and future GLONASS constellation is then presented for different locations around the world.

Investigating Ionospheric Scintillation Effects on Multifrequency GPS Signals

Over the last 15 years, the satellite constellation of the global positioning system (GPS) has been modernized for more precise applications, with the introduction of the L2C and L5 signals. However, among other effects, they are susceptible to severe ionospheric effects, particularly in the equatorial and low-latitude regions. Equatorial plasma bubbles, resulting from the combination of the ionospheric electrodynamics with plasma instability mechanisms and thermospheric coupling, may generate irregularity structures with scale sizes ranging from hundreds of kilometers to a few meters (or less). Ionospheric irregularities may cause deep amplitude fades and phase shifts to transionospheric signals. That is, they are responsible for amplitude and phase scintillation, which degrade receiver operations and may cause failures and unavailability to positioning and navigation services under extreme conditions. The objective of the present work is to analyze ionospheric scintillation effects on the L2C and L5 GPS signals, to compare their vulnerabilities with those of the L1 signal. The data used in this analysis were collected between November 2014 and March 2015, during the maximum solar activity of cycle 24 (a period of great scintillation incidence), by scintillation monitors deployed at four different sites in the Brazilian territory: Fortaleza, Presidente Prudente, Sao Jose dos Campos, and Porto Alegre. Intensity fades will be analyzed, considering different thresholds, to reveal their empirical probability distributions of scintillation occurrence, average fading occurrences and durations. The results will show that greater probabilities of strong scintillation occurrences are present in the modernized signals, reaching up to five times more events in the L5 signal in comparison with those in the legacy L1 signal. It will be shown that the L5 average fade duration is distinctly longer than the corresponding ones for the other frequencies, considering the same site, threshold, and L1 amplitude scintillation level. The results will also show that the average fade duration decreases according to the average ratio 0.6 s/3 dB within the threshold range from − 6 to − 15 dB, considering the same amplitude scintillation level and location.

Performance evaluation of tracking NavIC L5 signals under scintillation conditions

Ionosphere scintillation causes rapid and abrupt fluctuations in the intensity and phase of the signal due to the ionosphere irregularities. It is proved to be detrimental to the effective functioning of navigation systems. The reliability and integrity of GNSS system is dependent on the performance of signal tracking loops of the GNSS receivers which are adversely affected during scintillation. The study presents the analysis of the impact of scintillation on the receiver performance particularly carrier tracking loops which may provide cues of handling scintillation signals and overcome its drastic influence on the receiver functioning. The performance of the carrier tracking loop under scintillation is analysed and evaluated in terms of signal locking ability, correlator power, carrier to noise ratio and tracking error. The methodology involves generating simulated scintillation signals based on statistical model and modulating the real NavIC L5 signals with simulated scintillations to generate scintillated signal to test the performance of the software implemented carrier tracking loop. The study concludes with possible strategies such as adaptable loop bandwidth and extending integration time to subdue scintillation effects on receiver performance.

Signal‐In‐Space Performance Under Multiconstellation Environment From an Indian Low Latitude Station

AbstractGlobal 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.