GNSS Applications Research Articles

Design and Implementation of a Tri-Band Miniaturized Planar Inverted-F Antenna with Double Resonator for GPS Application

In this paper, a new planar inverted-F antenna is presented for GNSS applications and the DCS band. The proposed antenna structure is based on capacitive slots that achieve multiband behavior. The antenna has two resonators of dimensions (31mm×17mm×0.35mm) and (20.5mm×17.5mm× 0.35mm), a ground plane (60mm×17.5mm×0.35mm) and 6.5mm height. A prototype was implemented and good agreement was noticed between the simulation and test results, indicating three resonant frequencies, namely 1.176GHz, 1.8GHz and 2.8GHz. Radiation characteristics and diversity performance of the proposed structure is presented with detail.

GPS satellite inter-frequency clock bias estimation using triple-frequency raw observations

This study proposes a unified uncombined model to estimate GPS satellite inter-frequency clock bias (IFCB) in both triple-frequency code and carrier-phase observations. In the proposed model, the formulae of both phase-based and code-based IFCBs are rigorously derived. Specifically, satellite phase-based IFCB refers to its time-variant part and it is modeled as a periodic function related to the sun–spacecraft–earth angle. A zero-mean condition of all available GPS satellites that support triple-frequency data is introduced to render satellite code-based IFCB estimable. Three months of data from 40 globally distributed stations of the International GNSS Service Multi-GNSS Experiment are used to test our method. The results show that the four-order periodic function is suitable for eliminating the 12-h, 6-h, 4-h, and 3-h periods that exist in the a posteriori phase residuals when no periodic function is used. For comparison, the geometry-free and ionosphere-free (GFIF) phase combination and differential code bias (DCB) products released by DLR (German Aerospace Center) and IGG (Institute of Geodesy and Geophysics, China) are also used to calculate the satellite phase-based and code-based IFCBs, respectively. The results show that (1) the average root mean square (RMS) of the phase-based IFCB difference between the proposed method and the GFIF phase combination is 4.3 mm; (2) the average RMS in the eclipse period increased by 50% compared with the average RMS in the eclipse-free period; (3) the mean monthly STD for code-based IFCB from the proposed method is 0.09 ns; and (4) the average RMS values of code-based IFCB differences between the proposed method and the DCB products released by DLR and IGG are 0.32 and 0.38 ns. This proposed model also provides a general approach for multi-frequency GNSS applications such as precise orbit and clock determination.

Validation of NeQuick 2 Model Topside Ionosphere and Plasmasphere Electron Content Using COSMIC POD TEC

AbstractAn accurate representation of the topside ionosphere and plasmasphere electron content is still one of the important issues for ionospheric models, particularly for those used in GNSS applications. In this work, a validation of NeQuick 2 empirical ionospheric model has been performed in terms of ionosphere topside and plasmasphere electron content in the altitude range ~800–20,200 km. For this purpose, total electron content (TEC) data derived from precise orbit determination (POD) antennas onboard COSMIC low earth orbit (LEO) satellites tracking GPS signals have been used. The data span the period from 2006 to 2018 and correspond to different heliogeophysical conditions. In order to remove unrealistic TEC values from the validation process, a specific filtering procedure has been applied to POD‐derived TEC data. Subsequently, the statistical analysis of the difference between the modeled and the corresponding experimentally derived TEC values has been performed on data obtained during geomagnetically quiet periods. The results are presented as a function of solar activity level, season, local time, and geomagnetic latitude plots. They show that NeQuick 2 model underestimates the ionosphere topside and plasmasphere electron content, particularly during the early morning hours. The conditions under which the discrepancy between the model and experimental data is the highest have been also identified and considered as indications for future model improvements.

Smart lock system for Airbnb Platform using global navigation satellite system services

Over the last two decades, the world changes have occurred faster and faster. The services provided by GNSS represent major business drivers. Innovative and effective GNSS applications such as location-based smart-phone and hand-held device apps, navigation services and fleet management represent value-added services. The smart lock system is based on the Airbnb [1] platform for lease or rent short-term lodging and solves both a technical/operational limitation and trustfulness issue [2]. The solution is to link the housing, the reservation number and the mobile phone of the customer so that, with the help of localization services, the smart lock of the apartment could be opened only by the person wearing the mobile device, when that person reaches the destination, and only in the specified period of time when the reservation is made. The proposed solution adds value to the already implemented idea, and the targeted market is almost worldwide and can be extended also for car rentals and other rent services.

A Novel Approach to Improve GNSS Precise Point Positioning During Strong Ionospheric Scintillation: Theory and Demonstration

At equatorial latitudes, ionospheric scintillation is the major limitation in achieving high-accuracy GNSS positioning. This is because scintillation affects the tracking ability of GNSS receivers causing losses of lock and degradation on code pseudorange and carrier phase measurements, thus degrading accuracy. During strong ionospheric scintillation, such effects are more severe and GNSS users cannot rely on the integrity, reliability, and availability required for safety-critical applications. In this paper, we propose a novel approach able to greatly reduce these effects of scintillation on precise point positioning (PPP). Our new approach consists of three steps: 1) a new functional model that corrects the effects of range errors in the observables; 2) a new stochastic model that uses these corrections to generate more accurate positioning; and 3) a new strategy to attenuate the effects of losses of lock and consequent ambiguities re-initializations that are caused by the need to re-initialize the tracking. We demonstrate the effectiveness of our method in an experiment using a 30-day static dataset affected by different levels of scintillation in the Brazilian southeastern region. Even with limitations imposed by data gaps, our results demonstrate improvements of up to 80% in the positioning accuracy. We show that, in the best cases, our method can completely negate the effects of ionospheric scintillation and can recover the original PPP accuracy that would have existed without any scintillation. The significance of this paper lies in the improvement it offers in the integrity, reliability, and availability of GNSS services and applications.

Between-satellite single-difference integer ambiguity resolution in GPS/GNSS network solutions

In various GNSS applications with high requirements for precision, integer ambiguity resolution (IAR) is of great significance for taking full advantage of precise carrier-phase observations. Until now, there are two approaches to achieving IAR in network solutions, i.e., to resolve double-difference (DD) integer ambiguities or to resolve zero-difference (ZD) integer ambiguities. In this paper, we will present an approach to resolving between-satellite single-difference (BSSD) integer ambiguities in network solutions. BSSD ambiguity fixing can be divided into two main steps: Firstly, WL satellite FCBs are estimated to help to fix WL BSSD ambiguities and then narrow-lane (NL) BSSD ambiguity resolution is performed in a bootstrapping mode: datum BSSD ambiguities are selected and compulsorily fixed to the nearest integers and then a standard sequential fixing procedure is employed for the remaining independent BSSD ambiguities. Network solutions with GPS data from about 130 stations were conducted to validate the proposed approach. Experimental results show that the quality of satellite orbits, station coordinates and satellite clocks obtained with the new approach was almost the same as that with the DD approach. It is also shown that the new approach enjoyed slightly higher fixing ratio for both WL and NL ambiguities and was superior in computation efficiency, e.g., an improvement of 60% on average was achieved in this study. As demonstrated by experiments of precise point positioning (PPP) with 30-min data, satellite clocks achieved with the new approach have the ability to support IAR in PPP, just like those achieved with ZD IAR approach.

A new model for reduction of Azimuth asymmetry biases of tropospheric delay

ABSTRACTNowadays, a GNSS application is one of the main backbones of lifestyle. The GNSS signal that comes from space satellites to receivers on Earth suffers some delays. The troposphere layer is one of the basic sources of delay to signals. To detect the delay, many models have been produced taking into account the receiver location and satellite zenith angle. Most of these models give vertically perfect representation without accounting the horizontal asymmetry effect. The horizontally graded difference “azimuth asymmetry” is negligible at high elevation angles up to 10°. At low elevation angles, the asymmetry is significant. At 2° elevation angle, the asymmetry is about 72 mm for east and west and about 66 mm for south. Using the Precise Tropospheric Delay Database (PTD), the difference in horizontal plane delays is studied. A new model is proposed and compared to PTD calculations. The model has three coefficients obtained for high zenith angles (70° to 88°). These coefficients are modelled as a function of zenith angle and used to give a horizontal gradient factor which is multiplied by the northern mapping function to map it to any azimuth. The proposed model makes significant improvement. For east and west directions, the model decreases the bias from around 72 mm to be about 1.0 mm. For the southern direction, the produced model needs an improvement to get closer to the true asymmetry.Abbreviations: GNSS: Global Navigation Satellite Systems; HG: Horizontal Gradient; MF: Mapping Function; PTD: Precise Tropospheric Delay Database; Z: Zenith Angle; ZHD: Zenith Hydrostatic Delay; ZTD: Zenith Total Delay; ZWD: Zenith Wet Delay

Time Series of Land subsidence rate on Coastal Demak Using GNSS CORS UDIP and DINSAR

Most of the studies land subsidence and impact have been done on the north coastal area of Java, especially Semarang and Demak. This landsubsidence has a very serious impact both in the infra structure, the economy and the environment. Techniques of observing landsubsidence using geodetic methods have been widely practiced. Geodetic technology is undergoing rapid development, especially in GNSS navigation satellite technology as well as satellite radar interferometry. Both have advantages and disadvantages of each. In this study will examine the application of DinSAR interferometric techniques and GNSS technology to predict the rate of land subsidence coastal of Demak regency. This paper also emphasize the role of GNSS and DinSAR application in deformation especially for landsubsidence monitoring.

Deformation Monitoring of Reservoir Dams Using GNSS: An Application to South-to-North Water Diversion Project, China

Deformation monitoring plays an important role in performance monitoring to ensure the reservoir dams and embankments are functioning as designed. This work should be the first deformation monitoring application of GNSS in China's huge South-to-North Water Diversion Project. A GNSS deformation monitoring system, equipped with 4G data transmission and automated data processing software, is established at Shuangwangcheng Reservoir, an important regulation control project on the Eastern Route. Precision evaluations of different observation sessions from both GPS and BDS are conducted, and results show that the performance of BDS is comparable to that of GPS, especially for longer observation session solutions. The 1 mm horizontal and 2 mm vertical precisions of daily solutions meet the deformation monitoring requirement of the project. The deformation time series reveal an uneven settlement of Shuangwangcheng Reservoir dam. The causes of deformation are analyzed and the water level change in the reservoir is deemed as the main factor.

Application of GNSS for UAVs

Application of GNSS for UAVs

Dual-frequency carrier smoothed code filtering with dynamical ionospheric delay modeling

In GNSS applications, carrier-smoothed-code is a widely used technique to combine code pseudo-range and carrier phase measurements. A dynamical ionospheric delay modeling method is proposed based on Kalman filter and least-squares theory. The level of the process noise is adaptively tuned along with the real-time KF state estimation, based on the online variance component estimation method. Meanwhile, the correlations of the time differenced carrier phase measurements are considered. This approach avoids overly optimistically evaluating the estimate and improves the transient accuracy of the estimates. A real GPS dataset is employed to check the performance of the proposed method under different conditions. The results show that the new algorithm can model the ionospheric delay variation well with different sampling intervals or even in ionospheric abnormal environment. The positioning accuracy can be confirmed, about 21%, 35% and 16% better are obtained in the N, E, and U direction than raw dataset.

Multi-GNSS triple-frequency differential code bias (DCB) determination with precise point positioning (PPP)

Differential code biases (DCBs) account for the most significant systematical biases when sensing the earth’s ionosphere with GNSS observations and are also important correction parameters in GNSS applications of positioning, navigation and timing. With the continuous modernization of the American GPS and Russian GLONASS systems, and also the rapid developments of the European Galileo and Chinese BeiDou systems, there is a strong demand of precise satellite DCB products for multiple constellations and frequencies. This study proposes a new method for the precise determination of multi-GNSS triple-frequency DCBs, which can be divided into three steps. The first step is to precisely retrieve slant ionospheric delays and “additional code biases” based on a newly established full-rank triple-frequency precise point positioning (PPP) model with raw observations. Both the slant ionospheric delays and “additional code biases” containing the DCBs need to be estimated. Then, an enhanced IGGDCB (IGG stands for Institute of Geodesy and Geophysics) method is used to estimate the DCBs between the first and second frequency bands with the PPP-derived slant ionospheric delays. At last, the previously estimated DCBs between the first and second frequency bands are substituted into the “additional code biases” and DCBs between the first and third frequency bands are estimated. Multi-GNSS slant ionospheric delays from the triple-frequency PPP method are compared with those from the traditional dual-frequency carrier-to-code level (CCL) method, in terms of formal precision and zero-baseline experiment. Quad-system average formal precisions are 0.08 and 0.41 TECU, for PPP and CCL methods, respectively, indicating the obvious improvements of PPP over CCL. One month of data from 60 globally distributed multi-GNSS experiment stations are selected, and totally eight types of DCBs are estimated for GPS, GLONASS, Galileo and BeiDou. Multi-GNSS satellite DCBs generated with the proposed method are compared with the products from different agencies, including Center for Orbit Determination in Europe (CODE), Deutsches zentrum fur Luft-und Raumfahrt (DLR) and Chinese Academy of Sciences (CAS). For GPS C1WC2 W DCBs, RMS values with respect to CODE products are 0.24, 0.07 and 0.09 ns for DLR, CAS and IGG (this study), respectively. RMS values are 0.31/0.25 and 0.19/0.15 ns, for GPS C1WC5X and C1WC5Q DCBs and with respect to DLR/CAS, respectively. For GLONASS C1PC2P DCBs, RMS values with respect to CODE are 0.68, 0.49 and 0.33 ns for DLR, CAS and IGG, respectively. For Galileo, RMS values are 0.16/0.20 and 0.13/0.14 ns, for C1XC5X and C1XC7X DCBs and with respect to DLR/CAS, respectively. For BeiDou, RMS values are 0.32/0.25 and 0.34/0.41, for C2IC7I and C2IC6I DCBs and with respect to DLR/CAS. These results show that the proposed method can provide multi-GNSS and multi-frequency satellite DCB estimation with high precision, processing efficiency and flexibility.

Variations and modeling of the atmospheric weighted mean temperature for ground-based GNSS applications: Central Arabian Peninsula

In this study, 107,776 radiosonde observations from seven sites in Saudi Arabia for the period 1985–2016 were used to calculate the atmospheric weighted mean temperature (Tm) and investigate its variations. The results showed that the Tm exhibited a seasonal cycle, with a maximum Tm during summer and a minimum Tm during winter. For each site, and for the combined data from all sites, a simple empirical model was developed and tested to predict the Tm based on surface temperatures. The predictability of fourteen Tm-Ts (surface air temperature) models proposed by several investigators was carried out. The predictions of these models differ from one site to another. While some models give adequate predictions for one site, they fail in others. However, some models present reasonable estimates when the measured data from all sites are combined. Comparisons between measured (from radiosonde observations) and calculated precipitable water vapour (PWV) values for some sites using different Tm values were carried out. By using the site specific Tm-Ts models, the mean bias error (MBE) and root mean square error (RMSE) were below one 1 mm, and between 4 and 5 mm, respectively. On the other hand, the regional developed model developed by this study gives sub-mm MBE values and about 12 mm RMSE. Using seven of the Tm-Ts models found in the literature, the PWV values were calculated for the same selected sites. The accuracies of these models are comparable with those developed in this study for each site.

Software tools for GNSS interferometric reflectometry (GNSS-IR)

GNSS-R interferometric reflectometry (also known as GNSS-IR, or GPS-IR for GPS signals) is a technique that uses data from geodetic-quality GNSS instruments for sensing the near-field environment. In contrast to positioning, atmospheric, and timing applications of GNSS, GNSS-IR uses the signal-to-noise ratio (SNR) data. Software is provided to translate GNSS files, map GNSS-IR reflection zones, calculate GNSS-IR Nyquist frequencies, and estimate changes in the height of a reflecting surface from GNSS SNR data.

Prediction of Multipath Interference for Static GNSS Applications

Prediction of Multipath Interference for Static GNSS Applications

Quality assessment of GNSS observations from an Android N smartphone and positioning performance analysis using time-differenced filtering approach

The development of low-cost GNSS chips inspired the development of advanced positioning, navigation and timing devices. In ‘I/O of 2016’, Google announced that GNSS observations from devices running the Android version 7 operating system would be available to developers. Providing GNSS application developers the opportunity to develop advanced processing algorithms for accurate position estimation using pseudorange, Doppler and carrier phase observations. The quality of GNSS observations from Android smartphones and their accuracy in estimating position is assessed. The observed carrier-to-noise density ratio (C/N0), pseudorange noise, pseudorange rate error and phase rate error of GNSS observations are evaluated. The results demonstrate that the average (C/N0) value is approximately 10 dB-Hz lower than the representative values obtained from a geodetic-quality antenna and receiver. The station single-difference pseudorange residuals on all available signals vary from − 20 to 20 m, and the value of pseudorange rate varies within ± 10 m/s. In addition, the phase rate and Doppler reaches approximately ± 0.2 m/s. Different from the geodetic receivers, the signal noise ratio (SNR) obtained from smartphone varies more significantly, regardless of elevation angle. Therefore, the SNR-dependent weighting method is preferred during data processing. Furthermore, the results of the static data analysis show that the horizontal and vertical RMS position errors are less than 0.8 and 1.4 m, respectively, when Doppler and phase observations are incorporated into the positioning solution.

Climatology of the scintillation onset over southern Brazil

Abstract. This work presents an analysis of the climatology of the onset time of ionospheric scintillations at low latitude over the southern Brazilian territory near the peak of the equatorial ionization anomaly (EIA). Data from L1 frequency GPS receiver located in Cachoeira Paulista (22.4∘ S, 45.0∘ W; dip latitude 16.9∘ S), from September 1998 to November 2014, covering a period between solar cycles 23 and 24, were used in the present analysis of the scintillation onset time. The results show that the start time of the ionospheric scintillation follows a pattern, starting about 40 min earlier, in the months of November and December, when compared to January and February. The analyses presented here show that such temporal behavior seems to be associated with the ionospheric prereversal vertical drift (PRVD) magnitude and time. The influence of solar activity in the percentage of GPS links affected is also addressed together with the respective ionospheric prereversal vertical drift behavior. Based on this climatological study a set of empirical equations is proposed to be used for a GNSS alert about the scintillation prediction. The identification of this kind of pattern may support GNSS applications for aviation and oil extraction maritime stations positioning. Keywords. Ionosphere (ionospheric irregularities; modeling and forecasting) – radio science (space and satellite communication)

A Novel Array-Based Spoofing and Jamming Suppression Method for GNSS Receiver

GNSS is now affecting in various aspects of human life, while it is susceptible to interference including jamming and spoofing, which will make itself be caught in serious risk. Therefore, reliable safeguards are urgently necessary to ensure the safety of GNSS applications. Array signals received by different array sensors contain the spatial characteristics of GNSS signals from different directions, which offer possible approaches to spoofing mitigation based on the general assumption that all spoofing pseudorandom noises are from the same direction. Given this, a novel array signal processing method is proposed in this paper, which can adaptively suppress jamming and spoofing and enhance the useful signals simultaneously. This proposed method can be compatible with the traditional GPS receiver without the need of adjusting the GPS receiver hardware. The effectiveness of this proposed method is verified by simulation results.

Novel wide-beam cross-dipole CP antenna for GNSS applications

A wide-beam circularly polarized (CP) cross-dipole antenna for GNSS applications is proposed in this article. This cross-dipole antenna is fed by a coaxial cable, on which the slots is added to optimize the impedance matching. These two pairs of dipole arms are designed with different lengths to obtain the circularly polarized radiation. Enhanced wide-beam CP radiation characteristics can be achieved by curving the dipole arms and adjusting the distance between the arms and the metallic ground plane. The study of proposed antenna performance with different geometric parameters has been conducted. The final antenna exhibits a good impedance bandwidth (IBW) of ∼13.1% (1.50-1.71 GHz), and the 3-dB axial-ratio bandwidth is over 7% (1.52-1.64 GHz). Broad pattern coverage of more than 140°, pure CP radiation at all designed bands and a wide 3 dB axial-ratio beamwidth (ARBW) of nearly 150° makes this antenna an excellent candidate for satellite communications and navigation systems.

Positioning performance of the NTCM model driven by GPS Klobuchar model parameters

Users of the Global Positioning System (GPS) utilize the Ionospheric Correction Algorithm (ICA) also known as Klobuchar model for correcting ionospheric signal delay or range error. Recently, we developed an ionosphere correction algorithm called NTCM-Klobpar model for single frequency GNSS applications. The model is driven by a parameter computed from GPS Klobuchar model and consecutively can be used instead of the GPS Klobuchar model for ionospheric corrections. In the presented work we compare the positioning solutions obtained using NTCM-Klobpar with those using the Klobuchar model. Our investigation using worldwide ground GPS data from a quiet and a perturbed ionospheric and geomagnetic activity period of 17 days each shows that the 24-hour prediction performance of the NTCM-Klobpar is better than the GPS Klobuchar model in global average. The root mean squared deviation of the 3D position errors are found to be about 0.24 and 0.45 m less for the NTCM-Klobpar compared to the GPS Klobuchar model during quiet and perturbed condition, respectively. The presented algorithm has the potential to continuously improve the accuracy of GPS single frequency mass market devices with only little software modification.