A precise Global Navigation Satellite System (GNSS) satellite orbit is an essential prerequisite for precise point positioning (PPP). Due to the daily orbit discontinuities (DODs) between adjacent daily orbit products provided by the International GNSS Service, the interpolation accuracy at the epochs near the day boundaries cannot be as high as expected and can significantly degrade the positioning

Reanalysis products have been applied to calculate the tropospheric delay for Global Navigation Satellite System (GNSS) positioning purposes widely. It is necessary to obtain high-precision tropospheric delay information from GNSS users with a high-precision tropospheric vertical stratification model because the height of the grids of the atmospheric reanalysis data is inconsistent with that of GNSS

The BeiDou-3 system uses the BeiDou Global broadcast Ionospheric delay correction Model (BDGIM) to describe global vertical total electron content (VTEC) distributions and provide ionospheric delay mitigations in single-frequency positioning. The transmission of BDGIM correction parameters in the navigation message of BeiDou-3 started in mid-2015. The limited coverage of BeiDou-3 transmitted BDGIM

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

Compared to the BeiDou regional navigation satellite system (BDS-2), the BeiDou global navigation satellite system (BDS-3) includes the newly designed B1C and B2a signals, which are compatible with the L1 and L5 frequencies of the global positioning system (GPS). Considering that the precise orbit determination (POD) of the BDS-3 constellation is currently restricted to the legacy B1I and B3I signals

We present the results of 10 years of research related to the development of a Rubidium vapor cell clock based on the principle of pulsed optical pumping (POP). Since in the pulsed approach, the clock operation phases take place at different times, this technique demonstrated to be very effective in curing several issues affecting traditional Rb clocks working in a continuous regime, like light shift

A near-real-time computerized ionospheric tomography (CIT) technique was developed over the East Asian sector to specify the 3-D electron density field. The technique is based on a plethora of Global Navigation Satellite System observables within the region of interest which is bounded horizontally 110°–160°E and 10°–60°N and extending from 80 to 25,000 km in altitude. Prior to deployment, studies

In the high orbit space, the visibility of GPS main lobe signal is poor due to the earth's occlusion and the increase in signal transmission distance. Therefore, the side lobe signals are essential for navigation mission, which puts forward higher requirements for the sensitivity of the receiver. In addition, the cross-correlation interference (CCI) caused by the large power difference between the

Micro-electro-mechanical system (MEMS)-based inertial measurement unit (IMU) together with single-frequency Global Navigation Satellite System (GNSS) receiver provides a cost-efficient solution for outdoor navigation. An accurate initial alignment is necessary to the GNSS/IMU integrated navigation system to guarantee a good performance. Existing in-motion alignment methods mostly rely on the velocity

We examine the sensitivity of the Global Positioning System (GPS) to non-tidal loading for a set of continental Eurasia permanent stations. We utilized daily vertical displacements available from the Nevada Geodetic Laboratory (NGL) at stations located at least 100 km away from the coast. Loading-induced predictions of displacements of earth’s crust are provided by the Earth-System-Modeling Group of

Due to poor local accuracy and temporal resolution, the GIM (global ionospheric map) application continues to be of restricted use in obtaining the characteristics of seismic-ionospheric effects. Utilizing spherical harmonic (SH) function and generalized trigonometric series (GTS), the latest 15 min/map GIM with high precision released from the Chinese Academy of Sciences (CAS), is expected to record

With the widespread application of global navigation satellite system, increasing amounts of gridded tropospheric data have been generated, increasing the difficulty of real-time transmission. We present that the global tropospheric grid data (GTGD) provided by Vienna mapping functions open access data have approximate sparse characteristics, and the compressed sensing (CS) method is used for sparse

With the rapid development of Global Navigation Satellite Systems (GNSS), precise point positioning (PPP) has been widely used for positioning, navigation, timing (PNT), and atmospheric sensing. Currently, the demand for low-cost single-frequency hardware is increasing. However, open-source single-frequency PPP (SFPPP) software, in particular those that employ uncombined GNSS observations, is scarce

Change detection within unequally spaced and non-stationary time series is crucial in various applications, such as environmental monitoring and satellite navigation. The jumps upon spectrum and trend (JUST) is developed to detect potential jumps within the trend component of time series segments. JUST can simultaneously estimate the trend and seasonal components of any equally or unequally spaced

Accurate timing is one of the key features of the Global Positioning System (GPS), which is employed in many critical infrastructures. Any imprecise time measurement in GPS-based structures, such as smart power grids, economic activities, and communication towers, can lead to disastrous results. The vulnerability of the stationary GPS receivers to the time synchronization attacks (TSAs) jeopardizes

Future generations of global navigation satellite systems (GNSSs) can benefit from optical technologies. Especially optical clocks could back-up or replace the currently used microwave clocks, having the potential to improve GNSS position determination enabled by their lower frequency instabilities. Furthermore, optical clock technologies—in combination with optical inter-satellite links—enable new

With the development of high-precision safety–critical applications using global navigation satellite systems (GNSS), fault detection and exclusion (FDE) is indispensable to guaranteeing the integrity of a GNSS positioning and navigation system. Many FDE algorithms have been developed based on the standard Kalman filter (KF), assuming that GNSS measurements come with Gaussian uncorrelated white noise

GNSS observation outage occurs inevitably in various situations, e.g., automobile driving in urban environments. Although the ambiguity resolution (AR) significantly shortens the initialization time of precise point positioning (PPP), frequent re-initialization of PPP AR may be needed due to outages. The inertial navigation system (INS) can be used for acquiring highly accurate position information

In a satellite navigation system, high-precision prediction of satellite clock bias directly determines the accuracy of navigation, positioning, and time synchronization and is the key to realizing autonomous navigation. To further improve satellite clock bias prediction accuracy, we establish a satellite clock bias prediction model by using long short-term memory (LSTM) that can accurately express

Global Navigation Satellite System (GNSS) tomography has proved its potential for sensing the three-dimensional (3D) distribution of atmospheric water vapor. Although the standard tomography model has improved, the geometry defect of GNSS acquisition remains a key problem and thus becomes the focus of this research. Thanks to the availability of high-resolution Moderate Resolution Imaging Spectroradiometer

For more than 20 years, precise point positioning (PPP) has been a well-established technique for carrier phase-based navigation. Traditionally, it relies on precise orbit and clock products to achieve accuracies in the order of centimeters. With the modernization of legacy GNSS constellations and the introduction of new systems such as Galileo, a continued reduction in the signal-in-space range error

Global navigation satellite systems (GNSSs) usually adopt constant-envelope multiplexing (CEM) techniques to deal with the nonlinear characteristic of high-power amplifiers (HPAs) on satellites. However, almost all the existing navigation signal CEM techniques assume that the bandwidth of the transmitter is large enough when compared to that of navigation signals, which often contradicts reality, especially

We have reconstructed integrated water vapor (IWV) using the zenith wet delays to track the properties of hurricanes and explore their spatial and temporal distributions estimated from 922 GPS stations. Our results show that a surge in GPS-derived IWV occurred at least six hours prior to the landfall of two major hurricanes (Harvey and Irma) that struck the Gulf and East Coasts of the USA in 2017.

A test campaign for carrier phase timing was conducted on the BDS/GNSS Open Testing Platform (BOTP), which was established by the National Time Service Center, Chinese Academy of Sciences (NTSC, CAS), using communication satellites in geosynchronous orbit. Its purpose was a navigation technology experiment and verification platform for BDS and GNSS. The system architecture of BOTP, a novel navigation

Monitoring sea level is critical due to climate change observed over the years. Global Navigation Satellite System Reflectometry (GNSS-R) has been widely demonstrated for coastal sea-level monitoring. The use of signal-to-noise ratio (SNR) observations from ground-based stations has been especially productive for altimetry applications. SNR records an interference pattern whose oscillation frequency

Non-line-of-sight (NLOS) global navigation satellite system (GNSS) signals are a major factor that limits the GNSS positioning accuracy in urban areas. An advanced GNSS signal processing technique, the vector tracking loop (VTL), has been applied to NLOS detection and correction, and its feasibility and superior performance have been reported in recent studies. In a VTL-based GNSS receiver, the navigation

The differential code biases (DCBs) of the global positioning system (GPS) receiver onboard low-Earth orbit (LEO) satellites are commonly estimated by a local spherical symmetry assumption together with the known GPS satellite DCBs from ground-based observations. Nowadays, more and more LEO satellites are equipped with GPS receivers for precise orbit determination, which provides a unique chance to

Gravity fields derived from GPS tracking of the three Swarm satellites have shown artifacts near the geomagnetic equator, where the carrier phase tracking on the L2 frequency is unable to follow rapid ionospheric path delay changes due to a limited tracking loop bandwidth of only 0.25 Hz in the early years of the mission. Based on the knowledge of the loop filter design, an analytical approach is developed

Global Navigation Satellite System raw measurements from Android smart devices make accurate positioning possible with advanced techniques, e.g., precise point positioning (PPP). To achieve the sub-meter-level positioning accuracy with low-cost smart devices, the PPP algorithm developed for geodetic receivers is adapted and an approach named Smart-PPP is proposed in this contribution. In Smart-PPP

The ionospheric delays and satellite differential code biases (DCBs) act as the significant error sources in the global navigation satellite system (GNSS) positioning, navigation and timing (PNT) services, and are still challenging to estimate correctly. In this study, the ionospheric vertical total electron content (VTEC) and satellite DCBs are estimated by a refining single-frequency precise point

High-rate precise point positioning with a global positioning system (GPS) is recognized as a powerful tool for large earthquake monitoring. However, its ability to monitor subdaily subtle deformation is still limited by unmodeled errors, which primarily contain the common-mode error (CME) and multipath. In this study, a combination of modified principal component analysis and the sidereal filtering

Low-earth-orbit (LEO) spacecraft formation flying (SFF) simulated on the Virginia Tech Formation Flying Testbed (VTFFTB) demonstrated the feasibility of detecting simplified ionospheric electron density (Ne) structures (i.e., one-dimensional equatorial plasma bubbles/EPBs) utilizing a differential total electron content (TEC) method. The Thermosphere-Ionosphere-Electrodynamics General Circulation Model

To meet the demands of precise orbit and clock determination, high-precision positioning, and navigation applications, a software called GREAT (GNSS + Research, Application and Teaching) was designed and developed at Wuhan University. As one important module in the GREAT software, GREAT-UPD was developed for multi-GNSS and multi-frequency uncalibrated phase delay (UPD) estimation. It can provide extra-wide-lane

Multipath signals formed by signal reflection coming from objects in the vicinity of Global Navigation Satellite System (GNSS) receivers result in a degradation of the tracking performance and an increase in the positioning error. By estimating the parameters of both line-of-sight signal and the multipath signals, superior multipath mitigation, spoofing suppression, and localization can be attained

Storm surges, one of the major causes of hurricane damage, lead to an abnormal rapid rise in water levels of up to a few feet for several minutes due to low pressure, strong winds, and high waves caused by a hurricane. This study utilizes GNSS-Reflectometry (GNSS-R) to monitor the unexpected water level change due to a storm surge using multi-frequency, multi-constellation GNSS. With an enhanced spectral

Single-difference (SD) ambiguity resolution (AR) and track-to-track (T2T) AR are two typical AR methods in precise orbit determination (POD) for Low Earth Orbit (LEO) satellites, which could improve the accuracy of orbits greatly. In this study, SD AR and T2T AR methods are introduced and analyzed. The performance of these two methods is assessed by three months of GPS observations from the Gravity

We present two different approaches to broadcasting information to retrieve the GNSS-to-GNSS time offsets needed by users of multi-GNSS signals. Both approaches rely on the broadcast of a single time offset of each GNSS time versus one common time scale instead of broadcasting the time offsets between each of the constellation pairs. The first common time scale is the average of the GNSS time scales

Unrepaired cycle slips in carrier phase measurements will result in re-initializing integer ambiguities, during which positioning accuracy will be compromised. However, the issue of cycle slip fixing has yet to be completely solved, which impedes the realization of continuous high-precision positioning, especially in real-time precise point positioning applications. Traditional cycle slip (detection

Apart from positioning accuracy, the reliability of a navigation system is also significant, especially for safety–critical applications, such as intelligent vehicle navigation. Generally, the Global Navigation Satellite System (GNSS) positioning algorithm assumed that measurement noise is uncorrelated white noise. However, the appearance of colored noise, which comes from various noise sources, does

While precise point positioning ambiguity resolution (PPP AR) is a valuable tool of the multi-constellation global navigation satellite system (multi-GNSS), phase biases are critical to implement PPP AR. Multi-frequency phase biases and satellite attitude files are provided freely by Centre National d’Etudes Spatiales (CNES), which are estimated based on GeoForschungs Zentrum (GFZ) satellite rapid

The BeiDou navigation satellite system (BDS) tracks medium earth orbit (MEO) satellites using only regional tracking stations in China. As a result, the broadcast clock accuracy of the MEO satellites decreases rapidly during the invisible arcs because of the lack of available observations. The inter-satellite link (ISL) technology of the third generation of BDS (BDS-3) can be used to extend the visible

Snow is an important water resource that plays a critical role in the global climate and hydrological cycle. Thus, Global Navigation Satellite System Interferometric Reflectometry (GNSS-IR) has emerged as a new remote sensing technology for monitoring snow depth. We developed the snow parameter processing software GiRsnow, based on GNSS-IR tools and a MATLAB environment, to obtain robust and effective

When observed from the ground, the frequency of the atomic clocks flying on the satellites of a Global Navigation Satellite System is referred to as apparent frequency, because it is observed through the on-board signal generation chain, the propagation path, the relativistic effects, the measurement system, and the clock estimation algorithm. As a consequence, the apparent clock frequency is affected

The nonideal characteristics of the entire channel of satellite navigation signals from generation, propagation to reception will cause signal distortions, resulting in pseudorange biases. Such kind of biases cannot be eliminated by differential technologies and has become a core error source in high-accuracy applications. We study the theoretical model and implementation method of a pseudorange-bias-free

Ionospheric scintillation is one of the most challenging problems in Global Navigation Satellite Systems (GNSS) positioning and navigation. Scintillation occurrence can not only lead to an increase in the probability of losing the GNSS signal lock but also reduce the precision of the pseudorange and carrier phase measurements, thus leading to positioning accuracy degradation. Statistical models developed

The fast and high-precision positioning with multiple Global Navigation Satellite Systems (multi-GNSS) has been challenging for decades. Although the single-frequency single system (SF-SS), satellite selection for multi-GNSS, and multi-GNSS-based partial ambiguity resolution (PAR) can achieve rapid positioning, the varying theoretical bases of them result in different fixed reliability of ambiguities

In order to improve the interoperability within the Global Navigation Satellite System (GNSS), the International Committee on Global Navigation Satellite Systems published a joint statement in December 2019 that stated that all GNSS providers agree to monitor and broadcast the time offsets between each system timescale and the Universal Time Coordinated (UTC) or the rapid realization of UTC (UTCr)

In recent years, with the rapid development of automated driving technology, the task for achieving continuous, dependable, and high-precision vehicle navigation becomes crucial. The integration of the global navigation satellite system (GNSS) and inertial navigation system (INS), as a proven technology, is confined by the grade of inertial measurement unit and time-increasing INS errors during GNSS

Knowledge of the signal-in-space (SIS) anomaly probability is important for the integrity monitoring of satellite navigation. An efficient SIS anomaly detection method is indispensable for characterizing the probability of SIS anomalies with sufficient confidence. The traditional GPS anomaly detection method based on the zero-mean Gaussian distribution assumption of the instantaneous signal-in-space

Precise baseline determination (PBD) is usually required for formation-flying satellite missions. For that purpose, the classical least squares (LS) estimation has been widely used for parameter estimation. It is known, however, that the LS estimation is highly sensitive to outliers in observations. Due to this fundamental defect, the LS estimation may fail to fulfill sub-millimeter or even millimeter

In a GPS-denied environment, even the combination of GPS and Inertial Navigation System (INS) cannot provide location reliably and accurately. We propose a new denoised stereo Visual Odometry VO/INS/GPS integration system for autonomous navigation based on tightly coupled fusion. The presented navigation system can estimate the location of the vehicle in either GPS-denied or low-texture environments

A Solar Radio Burst (SRB) is one of the most severe natural hazards affecting the performance of the global navigation satellite systems (GNSS). Considering the influence of different threat factors, the GNSS developers upgrade the systems to amend the accuracy and noise-proof features of the systems. In particular, GPS gradually replaces “old” satellites (GPS IIA, GPS IIR-A, GPS IIR-B) with new-generation

The combined use of multi-GNSS systems in positioning, navigation and timing requires taking into account the variable time offset between the individual system times. This offset can be determined at the user level as an additional unknown in the position-velocity-time (PVT) solution when a sufficient number of satellites is visible. However, a known value of the inter-system bias can also be injected

Coordinated Universal Time (UTC) is the worldwide standard of time, and UTC (k) is its physical implementation by any participating laboratory k. We describe a one-way real-time time service system that relies on GNSS to provide a realization UTC (NTSC) of China’s National Time Service Center, to a precision of sub-nanosecond. The system is inexpensive, easy to implement, and has been tested.

Solar radiation pressure (SRP) is the dominant non-gravitational perturbation for GPS satellites. In the IGS (International GNSS Service), this perturbation is modeled differently by individual analysis centers (ACs). The two most widely used methods are the Empirical CODE orbit Model (ECOM, ECOM2) and the JPL GSPM model. When using ECOM models, a box-wing model or other a priori models, as well as

We have proposed a new simplified zenith tropospheric delay model for Global Navigation Satellite System (GNSS) real-time applications using 10 years of numerical weather prediction data from the National Center for Environmental Prediction (NCEP). Our proposed model is a blind model in which the atmospheric input parameters are tabulated based on realistic atmospheric behavior. The model with only

The global navigation satellite system (GNSS) provides outstanding positioning services for outdoor activities with sufficient accuracies, but it has poor indoor performance. Indeed, indoor positioning is also expected to achieve the outdoor positioning level to cater to an even higher volume of user demands. A pseudolite (PL), also called a pseudosatellite, is a ground-based positioning system that

Reliable and correct carrier phase ambiguity resolution is the key to global navigation satellite system (GNSS) high-precision navigation and positioning applications. For kinematic situations, such as moving-baseline-based positioning and attitude determination, the baseline length between two antennas is constant; such a priori information could contribute to integer ambiguity resolution, especially

We propose a new data analysis process that is referred to as the upsampled common-view (UCV) method, which evolved via the interpolation techniques of portable clock trips and digital signal processing. By interpolating the locally measured global positioning system (GPS) P3 code time offsets to obtain global visible common-view (CV)-like results, we increase the number of data points at each epoch;

The time-hopping direct sequence spread spectrum (TH-DSSS) signal has been widely used in Pseudolites Positioning Systems to overcome the near-far problem. To capture the TH-DSSS signal, an additional parameter representing the time-hopping (TH) rules should be estimated in addition to the PRN code phase and carrier Doppler. However, the techniques of estimating a TH parameter in existing TH-DSSS signal