Multi-frequency GPS Research Articles

A study of equatorial plasma bubble structure using VHF radar and GNSS scintillations over the low-latitude regions

Ionospheric irregularities can cause detrimental effects on the global navigation satellite system (GNSS) signals, often in the form of rapid fluctuations in both amplitude and phase. Over the low-latitude regions, the equatorial plasma bubble (EPB) frequently arises after sunset, leading to GNSS scintillations since the signals propagate through ionospheric irregularities. The relationship between amplitude ionospheric scintillations (S4 index) on GNSS signals and EPB characteristics is presented. We investigate the geometrical relationship between backscatter echoes associated with the EPB and the multi-constellation and multi-frequency scintillations, specifically, GPS and Galileo constellations with L1/E1 and L5/E5a signals. By analyzing the GNSS scintillations along the GNSS signal paths, the GNSS ionospheric pierce points (IPPs) are mapped with S4 index at different altitudes and projected along the magnetic field line together with the backscatter echoes at the equatorial atmosphere radar (EAR), West Sumatra, Indonesia. Our results are obtained for moderate scintillation cases due to limited data available for this study. The results show the EPB impact ionospheric scintillations. The S4 index on the L5/E5a signal is more susceptible to scintillations than the L1/E1 signal. Moreover, we found a high correlation between EAR backscatter echoes and S4 values on both L1/E1 and L5/E5a at an altitude between 250 and 350 km, indicating that the EPB occurs on the bottomside of the ionosphere.

Modeling multifrequency GPS multipath fading in land vehicle environments

The reliability and performance of GPS receivers depend on the quality of the signal received, which can be largely affected by the interference caused by buildings, trees, and other obstacles. Since obstacles are always present in practical applications, several statistical representations have been developed along the years to measure, predict, and compensate errors induced by interferences. Two of the most used models to characterize GPS signal fading are the Nakagami-m and Rice, but in this work, we present evidence that supports the κ–μ distribution as the best fit to deal with multifrequency GPS multipath channels inside urban, rural, and forest areas. A synthetic signal simulator was developed to create propagation cases involving scattering clusters and specular reflections. Additionally, experimental measurements are presented to confirm the κ–μ distribution as the best distribution to characterize different situations on the available three GPS frequencies. We then present typical values of fading coefficients in L1, L2C, and L5 signals, for cases involving urban canyons, regular urban, rural, and dense vegetation areas. These coefficients can also be used to evaluate the receiver performance under similar cases or may be applied in weights measurement methods for positioning computation improvement.

Generalized Multifrequency GPS Carrier Tracking Architecture: Design and Performance Analysis

This article presents a generalized multifrequency carrier tracking architecture applicable to multifrequency global navigation satellite system receivers operating in frequency-selective fading environments. This architecture unifies a conventional single-frequency-independent tracking (ST) mode, which only operates on measurements from a single carrier, a multifrequency joint tracking (JT) mode, which linearly combines measurements from multiple carriers, and a multifrequency optimal tracking (OT) mode, which incorporates signal intensity in multicarrier combinations via an aggregate Kalman filter. The analytical closed-form expressions of the tracking error variance for the ST, JT, and OT modes are derived for theoretical analysis and comparison. Their tracking performances are evaluated and quantified using a simulated triple-frequency GPS signal with varying combinations of signal strengths. To have a fair assessment in real-world scenarios, real data collected during strong ionospheric, tropospheric scintillations, and multipath reflections and scattering are also used for performance evaluations in ST, JT, and OT modes.

Assessing the performance of multi-frequency GPS, Galileo and BeiDou PPP ambiguity resolution

ABSTRACT The authors investigate the benefits for the precise point positioning (PPP) ambiguity resolution technique of using the GPS L1, L2 and L5; Galileo E1, E5a, E5b and E6; and BeiDou B1, B2 and B3 measurements. Data from 17 reference stations over a period of 31 consecutive days in 2018 were used. It was found that the four-frequency Galileo combination of E1+E5a+E5b+E6 provides the lowest geometric and ambiguity variance. In a kinematic test using triple- and four-frequency GNSS measurements, the solution convergence time can be shortened by an average of 5 minutes as compared to the triple-frequency GPS-only PPP case.

Characterizing the Complex Two N‐Wave Ionospheric Signature of the 2016 Kaikoura Earthquake

AbstractMajor earthquakes (>∼6.5 Mw) can generate observable waves which propagate not only through the Earth but also through the Earth's ionosphere. These traveling ionospheric disturbances can be observed using multifrequency GPS receivers to measure the ensuing perturbations in the Total Electron Content of the ionosphere. Assisted by a statistical approach we developed to indicate the occurrence of a significant TEC perturbation from the normal background behavior, we detect a traveling ionospheric disturbance generated by the 2016 7.8 Mw Kaikoura earthquake occurring in New Zealand on the 13th of November. The disturbance was detected ∼8 min after the earthquake, propagating toward the equator at ∼1 km/s with a peak‐to‐peak amplitude of ∼0.22 Total Electron Content units. The coseismic waveform exhibits complex structure unlike that of the expected N‐wave for coseismic ionospheric disturbances, with observations of oscillations with 4‐min periodicity and of two N‐waves. This observed complexity in the ionosphere likely reflects the impact of the complex, multifault structure of the earthquake.

A Multifrequency GPS Signal Strong Equatorial Ionospheric Scintillation Simulator: Algorithm, Performance, and Characterization

This paper presents a physics-based, data-consistent, multifrequency GPS scintillation signal simulator. The simulator is based on the two-component power-law phase screen derived from real GPS scintillation measurements. The real data used to initialize the simulator, simulator outputs, and receiver-processed results are compared to demonstrate the simulator accuracy and the receiver processing effects. This simulator will enable better characterization of ionospheric scintillation effects and development of robust receiver algorithms during strong equatorial scintillation.

Ionospheric Scintillation Simulation on Equatorial GPS Signals for Dynamic Platforms

This paper presents a physics-based, data-consistent, multifrequency GPS scintillation signal simulator for dynamic platforms in the equatorial region. This simulator is based on a two-dimensional two-component power-law phase screen model which is described by a compact set of parameters. The time scale factor is mainly investigated in this paper, which determines the decorrelation time of the simulation signal and is affected by various factors including propagation geometry, irregularity drift velocity, and dynamics of the platform. The comparison between the initialization and simulation data for stationary receivers shows the effectiveness of the simulator. In addition, this paper examines the influence of the platform dynamics on simulation signals with respect to the geomagnetic field direction and the irregularity drift velocity. The simulator presented in this paper will provide a viable tool for dynamic GPS scintillation signal simulation and will aid the design for robust receiver processing algorithms during scintillation for dynamic platforms.

GNSS Jamming Resilience for Close to Shore Navigation in the Northern Sea

Navigational error accounts for half of the accidents and serious incidents in close to shore maritime transport in Norway predominantly due to the rapidly changing weather conditions and the dangerous nature of the narrow inshore waters found along the Norwegian coast. This creates a dependence on Differential Global Positioning System (DGPS) use and any disruption to this service can lead to an increased accident rate. The aim of this paper is to research the jamming vulnerability of existing maritime receivers and to understand if an upgrade to a multi-constellation or multi-frequency receiver would improve system resilience. The novelty of this work is a comparison of jamming resilience between different combinations of multiple constellations (GPS and Globalnaya Navigatsionnaya Sputnikovaya Sistema (GLONASS)) and multi-frequency Global Navigation Satellite System (GNSS) signals. This paper presents results from GNSS jamming trials conducted in the northern part of Norway, confirming previous research and indicating that typical maritime GPS receivers are easy to jam and may produce erroneous positional information. Results demonstrate that the single frequency multi-constellation receivers offer better jamming resilience than multi-frequency (L1 + L2) GPS receivers. Further, the GLONASS constellation demonstrated a better resilience than GPS. Results demonstrate a known correlation between GPS L1 and L2 frequencies, as well as a probable over-dependence on GPS for signal acquisition, meaning that no signal can be received without GPS L1 present. With these limitations in mind, the authors suggest that the most economic update to the single frequency GPS receivers, currently used for maritime applications, should be multi-constellation GPS + GLONASS receivers. This solution is cheaper and it also offer better jamming resistance for close to shore navigation than dual frequency receivers.

Comparison of the effect of high‐latitude and equatorial ionospheric scintillation on GPS signals during the maximum of solar cycle 24

AbstractRadio signal scintillation caused by electron density irregularities in the ionosphere affects the accuracy and integrity of Global Navigation Satellite Systems, especially in the equatorial and high‐latitude regions during solar maxima. Scintillation in these two regions, nevertheless, is usually influenced by different factors and thus has different characteristics that cause different effects on GNSS signals. This paper compares the characteristics of high‐latitude and equatorial scintillation using multifrequency GPS scintillation data collected at Gakona, Alaska, Jicamarca, Peru, and Ascension Island during the 24th solar maximum. Several statistical distributions are established based on the data to characterize the intensity, duration, and occurrence frequency of scintillation. Results show that scintillation in the equatorial region is generally more severe and longer lasting, while high‐latitude scintillation is, in general, more moderate and usually dominated by phase fluctuations. Results also reveal the different impacts of solar activity, geomagnetic activity, and seasons on scintillation in different geographic locations.