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Ground subsidence caused by underground coalmining result in the formation of ponding water on the ground surface. Monitoring the surface water level is crucial for studying the hydrologic cycle in mining areas. In this paper, we propose a combined technique using Global Navigation Satellite System Real-Time Kinematic (GNSS RTK) and GNSS Interferometric Reflectometry (GNSS-IR) to estimate the surface water level in areas of ground subsidence caused by underground coal mining. GNSS RTK is used to measure the geodetic height of the GNSS antenna, which is then converted into the normal height using the local height anomaly model. GNSS-IR is employed to estimate the height from the water surface to the GNSS antenna (or, the reflector height). To enhance the accuracy of the reflector height estimation, a weighted average model has been developed. This model is based on the coefficient of determination of the signal fitted by the Lomb-Scargle spectrogram and can be utilized to combine the reflector height estimations derived from multiple GNSS system and band reflection signals. By subtracting the GNSS-IR reflector height from the GNSS RTK-based normal height, the proposed method-based surface water level estimation can be obtained. In an experimental campaign, a low-cost GNSS receiver was utilized for the collection of dual-frequency observations over a period of 60 days. The collected GNSS observations were used to test the method presented in this paper. The experimental campaign demonstrates a good agreement between the surface water level estimations derived from the method presented in this paper and the reference observations. [ABSTRACT FROM AUTHOR]

Understanding ionospheric irregularities and their dynamics is crucial, with the rate of change of the total electron content index (ROTI) serving as a significant metric for this purpose. However, inconsistencies in ROTI magnitudes have been noted when sampled at one‐second interval across various Global Navigation Satellite System (GNSS) receivers. This study presents a detailed statistical analysis to investigate inconsistencies in ROTI using multi‐GNSS observations in conjunction with four distinct GNSS receiver types. Various factors affecting the ROTI inconsistencies among receivers were examined, including differences in sampling rates (1, 5, 15, and 30 s), and varying time window widths (1, 2, and 5 min). By examination of data obtained from GNSS receivers with zero or short baselines on a global scale, the analysis uncovered substantial variations in multi‐GNSS ROTI values across the four assessed receiver types. The main findings suggest that reducing the sampling rate reduces the inconsistencies in the magnitude of ROTI, particularly at lower sampling rates. This reduction can be attributed to the exclusion of high‐frequency components in the ROTI spectrum. Interestingly, the width of the time window is found to have minimal impact on the ROTI magnitude. The study also shows a direct correlation between a larger magnitude of ROTI and the increased noise in the signals tracked by receivers. These results emphasize the importance of considering sampling rates and GNSS receiver types when utilizing ROTI to investigate ionospheric irregularities. Plain Language Summary: Studying the changes in the ionosphere is important, and the rate of change of total electron content index (ROTI) is a key measure used for this purpose. ROTI is calculated using data from Global Navigation Satellite Systems (GNSS). However, variations in ROTI values were seen when measured at one‐second interval using different types of GNSS receivers. This study looked at these variations by analyzing ROTI data from multiple GNSS systems (BeiDou, GPS, GLONASS, and Galileo) and different types of GNSS receivers (Septentrio, Javad, Trimble, and Leica). Factors like sampling rates (1, 5, 15, and 30 s) and time window widths (1, 2, and 5 min) were considered during the analysis. The research found notable differences in multi‐GNSS ROTI values among the receiver types, with the Septentrio and Trimble receiver showing the most significant variations. Lowering the sampling rate led to fewer inconsistencies at slower rates, which is caused by a decrease in the multi‐GNSS ROTI values due to missing high‐frequency components. It was interesting to discover that the duration of the time window had little impact on ROTI values. These results stress the importance of paying attention to sampling rates and the type of GNSS receiver when using ROTI to study ionospheric irregularities. Key Points: Differences in multi‐GNSS ROTI values were observed across various receiver types at zero/short‐baseline stations globallyLowering the sampling rate decreased inconsistencies in the multi‐GNSS ROTI values among diverse receiversTime window width had a minimal impact on both the consistency and magnitude of multi‐GNSS ROTI values [ABSTRACT FROM AUTHOR]

Unpiloted technology requires attitude measurement from global positioning system to adjust the moving direction of car. However, the measurement result from the satellites suffer from fluctuation, which reduces the control ability of system. Thus, we propose our novel algorithm. First, it builds double difference observation equation based the measurements from two satellites. Second, the least squares algorithm is utilized to calculate double difference integer ambiguity. Third, it constructs the length of baseline to calculate baseline vector, which improves the solution success rate of integer ambiguity and reduces frequency of mutation occurs in attitude angle solving process. Finally, baseline vector is employed to solve the attitude angle of unpiloted car. The extensive experimental results demonstrate that the success rate of the attitude reach 95% within 2° of error under the constraint of the baseline, and the error of the attitude is less than 1° under the dynamic condition. [ABSTRACT FROM AUTHOR]

When processing the carrier phase, the global navigation satellite system (GNSS) grants the highest precision for geodetic measurements. The analysis centers (ACs) from the International GNSS Service (IGS) provide different data such as precise clock data, precise orbits, reference frame, ionosphere and troposphere data, as well as other geodetic products. Each individual AC has its own strategy for delivering the abovementioned products, with one of the key elements being the cutoff elevation angle. Typically, this angle is arbitrarily chosen using generic values without studying the impact of this choice on the obtained results, in particular when very precise positions are considered. This article addresses this issue. To this end, the article has two key sections, and the first is to evaluate the impact of using the two different cutoff elevation angles that are most widely used: (a) 3 degrees cutoff and (b) 10 degrees cutoff elevation angle. This analysis is completed in two major parts: (i) the analysis of the root mean square (RMS) for the carrier phase and (ii) the analysis of the station position in terms of repeatability. The second key section of the paper is a comprehensive carrier phase analysis conducted by adopting a new approach using a mean of the 25-point average RMS (A-RMS) and the single-point RMS and using an ionosphere-free linear combination. By using the ratio between the 25-point average RMS and the single-point RMS we can define the type of scatter that dominates the phase solution. The analyzed data span a one-year period. The tested GNSS stations belong to the EUREF Permanent Network (EPN) and the International GNSS Service (IGS). These comprise 55 GNSS stations, of which only 23 GNSS stations had more than 95% data availability for the entire year. The RMS and A-RMS are analyzed in conjunction with the precipitable water vapor (PWV), which shows clear signs of temporal correlation. Of the 23 GNSS stations, three stations show an increase of around 50% of the phase RMS when using a 3° cutoff elevation angle, and only four stations have a difference of 5% between the phase RMS when using both cutoff elevation angles. When using the A-RMS, there is an average improvement of 37% of the phase scatter for the 10° cutoff elevation angle, whereas for the 3° cutoff elevation angle, the improvement is around 33%. Based on studying this ratio, four stations indicate that the scatter is dominated by the stronger-than-usual dominance of long-period variations, whereas the others show short-term noise. In terms of station position repeatability, the weighted root mean square (WRMS) is used as an indicator, and the results between the differences of using a 3° and 10° cutoff elevation angle strategy show a difference of −0.16 mm for the North component, −0.21 mm for the East component and a value of −0.75 mm for the Up component, indicating the importance of using optimal cutoff angles. [ABSTRACT FROM AUTHOR]

Ground subsidence caused by underground coalmining result in the formation of ponding water on the ground surface. Monitoring the surface water level is crucial for studying the hydrologic cycle in mining areas. In this paper, we propose a combined technique using Global Navigation Satellite System Real-Time Kinematic (GNSS RTK) and GNSS Interferometric Reflectometry (GNSS-IR) to estimate the surface water level in areas of ground subsidence caused by underground coal mining. GNSS RTK is used to measure the geodetic height of the GNSS antenna, which is then converted into the normal height using the local height anomaly model. GNSS-IR is employed to estimate the height from the water surface to the GNSS antenna (or, the reflector height). To enhance the accuracy of the reflector height estimation, a weighted average model has been developed. This model is based on the coefficient of determination of the signal fitted by the Lomb-Scargle spectrogram and can be utilized to combine the reflector height estimations derived from multiple GNSS system and band reflection signals. By subtracting the GNSS-IR reflector height from the GNSS RTK-based normal height, the proposed method-based surface water level estimation can be obtained. In an experimental campaign, a low-cost GNSS receiver was utilized for the collection of dual-frequency observations over a period of 60 days. The collected GNSS observations were used to test the method presented in this paper. The experimental campaign demonstrates a good agreement between the surface water level estimations derived from the method presented in this paper and the reference observations.

The non-nominal troposphere caused by hazardous horizontal tropospheric gradients poses a threat to the integrity of the safety–critical civil aviation precision approach supported by ground-based augmentation system (GBAS). The carrier phase-based monitors are widely applied for evaluating and detecting the non-nominal troposphere. However, the detection sensitivity of carrier phase-based monitor is limited by the reliability of ambiguity resolution. To isolate the impact of ambiguity resolution failure on the non-nominal troposphere monitoring, a two-step non-nominal troposphere monitor is proposed based on the multiple short-baseline reference receivers. The ambiguity resolution correctness and the non-nominal troposphere are sequentially monitored, respectively. The probabilities of false alarm and missed detection are dynamically allocated between the two-step monitoring to satisfy the integrity risk requirement. The real BDS dual-frequency data are utilized to test the proposed two-step monitoring method. The result shows that the detection sensitivity of the proposed method is improved by 40.5% when compared with the traditional single-step monitoring method. It has been demonstrated that the proposed method can effectively reduce the integrity risk of high-precision navigation service caused by the non-nominal troposphere. [ABSTRACT FROM AUTHOR]

When processing the carrier phase, the global navigation satellite system (GNSS) grants the highest precision for geodetic measurements. The analysis centers (ACs) from the International GNSS Service (IGS) provide different data such as precise clock data, precise orbits, reference frame, ionosphere and troposphere data, as well as other geodetic products. Each individual AC has its own strategy for delivering the abovementioned products, with one of the key elements being the cutoff elevation angle. Typically, this angle is arbitrarily chosen using generic values without studying the impact of this choice on the obtained results, in particular when very precise positions are considered. This article addresses this issue. To this end, the article has two key sections, and the first is to evaluate the impact of using the two different cutoff elevation angles that are most widely used: (a) 3 degrees cutoff and (b) 10 degrees cutoff elevation angle. This analysis is completed in two major parts: (i) the analysis of the root mean square (RMS) for the carrier phase and (ii) the analysis of the station position in terms of repeatability. The second key section of the paper is a comprehensive carrier phase analysis conducted by adopting a new approach using a mean of the 25-point average RMS (A-RMS) and the single-point RMS and using an ionosphere-free linear combination. By using the ratio between the 25-point average RMS and the single-point RMS we can define the type of scatter that dominates the phase solution. The analyzed data span a one-year period. The tested GNSS stations belong to the EUREF Permanent Network (EPN) and the International GNSS Service (IGS). These comprise 55 GNSS stations, of which only 23 GNSS stations had more than 95% data availability for the entire year. The RMS and A-RMS are analyzed in conjunction with the precipitable water vapor (PWV), which shows clear signs of temporal correlation. Of the 23 GNSS stations, three stations show an increase of around 50% of the phase RMS when using a 3° cutoff elevation angle, and only four stations have a difference of 5% between the phase RMS when using both cutoff elevation angles. When using the A-RMS, there is an average improvement of 37% of the phase scatter for the 10° cutoff elevation angle, whereas for the 3° cutoff elevation angle, the improvement is around 33%. Based on studying this ratio, four stations indicate that the scatter is dominated by the stronger-than-usual dominance of long-period variations, whereas the others show short-term noise. In terms of station position repeatability, the weighted root mean square (WRMS) is used as an indicator, and the results between the differences of using a 3° and 10° cutoff elevation angle strategy show a difference of −0.16 mm for the North component, −0.21 mm for the East component and a value of −0.75 mm for the Up component, indicating the importance of using optimal cutoff angles.

Today, land and ocean observations are crucial for monitoring climate change. The method of GNSS reflectometry is an opportunistic way to provide low-cost observations of many geophysical parameters. However, although this method has been the subject of numerous research studies, work is still in progress to improve its possibilities and fields of application. This paper focuses on GNSS reflectometry using carrier phase measurements for water altimetry measurements. The difficulties in implementing such a method lie in the need to collect a coherent signal and to solve the integer ambiguity value. In this context, the implementation of innovative signal processing is described, including the correlation of the reflected signals in dedicated software and the prolongation of the coherent integration time to enhance signal coherency. These processes were applied to data collected over Carcans-Hourtin Lake in France to compute the height of the reflection surface which was then compared to in situ GNSS buoy height measurements. The results show that at 300 ft (91.44 m), the differences between the lake heights measured with the buoy and with the reflectometry data can reach less than 1 cm for the L1, E1 and E5 GNSS signals. In addition, the slope of the geoid estimated with the reflectometry data is very consistent with that of the RAF20 geoid model, with a difference of up to less than 2 mm/km. [ABSTRACT FROM AUTHOR]

The GNSS performance is significantly degraded in urban or natural canyons because of the signal interferences caused by buildings, trees and slopes. Besides the multipath and non-line-of-sight receptions, the diffraction effect frequently occurs in urban and natural canyons to cause large errors when the Global Navigation Satellite System (GNSS) signals transmitting path is close to the obstruction edge. We first analyzed the characteristics of diffraction errors and proposed an obstruction adaptive elevation masks (OAEMs) determination method to eliminate the diffractions in the data processing. It shows that the diffraction error has an approximately linear pattern and was largely dependent on the horizontal distance of the diffraction point to the phase center of the GNSS antenna and the diffraction elevation. It can be far beyond the theoretical limitation of multipath error and achieve several phase wavelengths, and could have various patterns in time series, such as trend, period and regular or unregular fluctuations, according to the features or distributions of obstruction edges. We proposed an OAEMs determination method by detecting diffractions in time series subsections and mapping and stacking them in a hemispherical map. The results show that it can eliminate the large diffraction errors to reduce the outliers and large fluctuations in the time series, and the positioning precision and reliability could be improved to a large extent. Especially in vertical directions, the precision can be improved by more than 40%. [ABSTRACT FROM AUTHOR]

GNSS signals are so vulnerable that they can be easily jammed by accidental or malicious interference because of the low transmission power of satellites. Space-time array processing (STAP) technology is the most effective method for anti-jamming, but undesired bias is introduced by STAP, leading to signal distortion. Traditional methods usually calibrate antennas and apply distortionless algorithms to solve this problem. However, calibration is burdensome and cannot be widely used, and most distortionless algorithms require information on signal direction. Thus, these methods are not applicable in general array receivers. We propose the time-delay carrier phase bias estimation (TD-CPBE) algorithm for STAP bias correction, which does not need antenna calibration or signal direction information. TD-CPBE locates moments of jamming alterations, estimates the STAP-introduced carrier phase bias by open-loop tracking, and corrects bias with a phase shift in the tracking procedure. The simulation results show that TD-CPBE can effectively correct the STAP carrier phase bias with a residual error of less than 3°, which is close to that of the traditional distortionless algorithm, and the open sky experiment further verifies the proposed algorithm. Since TD-CPBE requires much less prior information, it is a very effective and applicable STAP carrier phase bias correction method. [ABSTRACT FROM AUTHOR]

The effective spoofing detection can prevent GNSS receiver from providing erroneous positioning, velocity and timing information. Most of the available multi-antennas carrier phase double difference-based spoofing detection methods, regardless of the aiding of inertial navigation system (INS), exploit the divergence in carrier phase double differences derived from the direction of arrival (DOA) characteristics of the authentic signal and spoofing signal. However, the traditional methods mainly implemented by dual-antenna GNSS receivers has spatial ambiguity and lacks global detection performance analysis. Furthermore, an INS-aided multi-antenna spoofing detection method is proposed without spatial ambiguity comparing the predicted signal DOA by INS and the vectoral carrier phase double differences measured by multi antennas. To analyze the influence of the antenna array baseline length and signal DOA on the detection performance, a comprehensive numerical simulation was conducted. The dead zone of the proposed detection method is revealed to assess the global spoofing detection performance. The effectiveness of the proposed method is verified under the GNSS positioning scenarios. In the worst case, spoofing signals can be effectively detected in 95.2% of the airspace under one time the wavelength antenna baseline configuration and in 99.3% of the airspace under five times the wavelength antenna baseline configuration, respectively.

ABSTRACTIndoor positioning with high accuracy plays an important role in different application scenarios. As a widely used mobile communication signal, the Long-Term Evolution (LTE) network can be well received in indoor and outdoor environments. This article studies a method of using different reference signals in the LTE downlink for carrier phase time of arrival (TOA) estimation. Specifically, a solution is proposed and a multipath tracking Software Defined Receiver (SDR) is developed for indoor positioning. With our SDR indoor positioning system, the pilot signals of the LTE signals are firstly obtained by the coarse synchronization and demodulation. Then, with the assistance of the pilot signals, the time delay acquisition, the multipath estimating delay lock loop (MEDLL) algorithm, and the multipath anomaly detection are sequentially carried out to obtain navigation observations of received signals. Furthermore, to compare the performance of different pilot signals, the Secondary Synchronous Signals (SSS) and Cell Reference Signals (CRS) are used as pilot signals for carrier phase-based TOA estimation, respectively. Finally, to quantify the accuracy of our multipath tracking SDR, indoor field tests are carried out in a conference environment, where an LTE base station is installed for commercial use. Our test results based on CRS show that, in the static test scenarios, the TOA accuracy measured by the 1-σ error interval is about 0.5 m, while in the mobile environment, the probability of range accuracy within 1.0 m is 95%.

The official launch of the Chinese BeiDou Navigation Satellite System with global coverage (BDS-3) presents significant opportunities for various applications, including precision agriculture and autonomous driving, among others. With its global spatial coverage and hybrid space constellation comprising geosynchronous Earth orbit (GEO), inclined geosynchronous orbit (IGSO), and medium Earth orbit (MEO) satellites, BDS can significantly contribute to various GNSS remote sensing applications that require real-time, precise water surface height measurements with high temporal and spatial resolution, such as in tidal monitoring. In this paper, we propose a carrier-phase-based method for BDS Reflectometry (BDS-R) to precisely retrieve real-time water surface height. Firstly, the BDS-R altimetry method is introduced, along with a detailed explanation of the data processing procedures. Secondly, a quality control method tailored to the characteristics of low-cost BDS devices is developed. Thirdly, a land altimetry experiment is conducted to evaluate the precision of BDS-R and analyze the specific contribution of the BDS hybrid constellation. Finally, a water surface altimetry experiment validates the real-time monitoring capabilities for low-cost BDS-R. The results indicate that low-cost BDS-R can achieve real-time centimeter-level water level monitoring with a temporal resolution of 1 s in lakefront environments. The performance of BDS-R can be significantly improved by the BDS hybrid constellation, particularly IGSOs. It is concluded that low-cost BDS-R has great potential for promoting ground-based GNSS remote sensing applications. [ABSTRACT FROM AUTHOR]

Global Navigation Satellite Systems (GNSS) are used to provide accurate position, navigation, and time (PNT) information to users in various sectors of our society including transportation. Augmentation systems such as differential GNSS (DGNSS), real-time kinematics (RTK), and Precise Point Positioning (PPP) improve the GNSS performance, and providing reliable measurements from its reference station is very crucial. To ensure safe and accurate PNT solutions, code and carrier measurements must be monitored for potential faults or a performance degrade. Although there exist numerous methods to model and monitor the measurements, research on the carrier phase measurements is not as extensive as the code measurements. This paper introduces a split of residuals into receiver noise and multipath components to customize their estimation according to their respective statistical properties. This study also proposes a method to use machine learning-based non-linear regression to effectively model and monitor potential faults in the GNSS measurements including the carrier phase. A training dataset is used to model the nominal quantities of GNSS measurement residuals, and inflation factors are applied to over-bound the fault-free residuals. These inflated residuals are coupled with uncertainty factors to compute thresholds for monitoring carrier phase residuals, and the effectiveness of the thresholds is validated with a test dataset by achieving the false alarm rate of 6.61 × 10 − 6 , slightly lower than the desired level of 10 − 5 . [ABSTRACT FROM AUTHOR]

A method is presented for isolating iodine isotopes from aqueous coolant of the nuclear power plants' first circuit. At first, all forms of iodine radionuclides are converted into molecular form by the sequential addition of a carrier–potassium iodide, as well as hydroxylamine chloride, nitric acid and potassium nitrite. Then molecular iodine is transferred into the gas phase and volatile iodine radionuclides are immobilized on a membrane impregnated with metallic silver. The main advantage of the method is high selectivity of iodine release in relation to radionuclides interfering with the measurement of its activity. [ABSTRACT FROM AUTHOR]

Copyright of Acta Scientiarum Naturalium Universitatis Sunyatseni / Zhongshan Daxue Xuebao is the property of Sun-Yat-Sen University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Ionospheric scintillation affects the positioning, navigation and timing services of the Global Navigation Satellite System (GNSS), calling for an urgent need for scintillation monitoring on a global scale. To monitor the ionospheric scintillation with each carrier of the 30-s sampling interval GNSS observations, a scintillation extraction method is proposed based on the Morse wavelet transform, together with the determination of the symmetry parameter, the time-bandwidth product, the characteristic frequency range and the threshold of the scintillation. After testing with four-year observations collected at 15 middle- and high-latitude stations, results show that the extracted scintillation indicator can detect the occurrence but fails to provide the magnitude of the scintillation with the 30-s-sampling-interval observations. Compared to the state-of-the-art scintillation index extracted from the ionospheric scintillation monitoring receiver, the proposed scintillation indicator is applicable in utilizing 30-s sampling interval GNSS observations to monitor scintillations in high-latitude regions, especially for those with long durations, hence making the widely available GNSS observations with low sampling intervals be introduced into the field of ionospheric scintillation monitoring on a global scale. [ABSTRACT FROM AUTHOR]

GPS precise point positioning (PPP) technique has been widely used in time and frequency transfer. The performance of PPP can be improved if the phase ambiguities are fixed to the correct integer number. In this study, GPS PPP integer ambiguity resolution (PPP AR) with CNES/CLS products is applied in time and frequency transfer. To eliminate the day boundary discontinuities and achieve continuous time and frequency transfer with GPS PPP AR, a method of modified satellites carrier phase continuity is proposed when multi-day GPS PPP AR solutions are calculated. In addition, to guarantee the robustness of time transfer results, a three-segment factor is used to adjust the variance of integer ambiguities constraints. Test results in comparison of PPP AR with an optical time link show that standard deviation is deduced about 40% and the frequency stability is improved about 50% for 3.5d averaging than BIPM PPP method. Besides, GPS PPP AR shows a better short-term frequency stability than BIPM IPPP while they show similar STD value and long-term frequency stability. Moreover, test results with zero-baseline, short-baseline and long-baseline time transfer links show that the average frequency stability improvement rates are about 40% compared with PPP float solutions, and about 30% compared with IGS final products when the averaging time is 21.3 h. [ABSTRACT FROM AUTHOR]

Indoor positioning with high accuracy plays an important role in different application scenarios. As a widely used mobile communication signal, the Long-Term Evolution (LTE) network can be well received in indoor and outdoor environments. This article studies a method of using different reference signals in the LTE downlink for carrier phase time of arrival (TOA) estimation. Specifically, a solution is proposed and a multipath tracking Software Defined Receiver (SDR) is developed for indoor positioning. With our SDR indoor positioning system, the pilot signals of the LTE signals are firstly obtained by the coarse synchronization and demodulation. Then, with the assistance of the pilot signals, the time delay acquisition, the multipath estimating delay lock loop (MEDLL) algorithm, and the multipath anomaly detection are sequentially carried out to obtain navigation observations of received signals. Furthermore, to compare the performance of different pilot signals, the Secondary Synchronous Signals (SSS) and Cell Reference Signals (CRS) are used as pilot signals for carrier phase-based TOA estimation, respectively. Finally, to quantify the accuracy of our multipath tracking SDR, indoor field tests are carried out in a conference environment, where an LTE base station is installed for commercial use. Our test results based on CRS show that, in the static test scenarios, the TOA accuracy measured by the 1-σ error interval is about 0.5 m, while in the mobile environment, the probability of range accuracy within 1.0 m is 95%. [ABSTRACT FROM AUTHOR]

Natural hazards and geomagnetic disturbances can generate a combination of atmospheric and ionospheric waves of different scales. The carrier phase of signals of global navigation satellite system (GNSS) can provide the highest efficiency to detect and study the weak ionospheric disturbances in contrast to total electron content (TEC) and TEC-based indices. We consider the border between the informative part of the carrier phase spectrum and the uninformative noises—the deviation frequency—as the promising means to improve the GNSS-based disturbance detection algorithms. The behavior of the deviation frequency of the carrier phase spectra was studied under quiet and disturbed geomagnetic conditions. The results showed that the deviation frequency value increases under magnetic storms. This effect was revealed for all GNSS constellations and signals regardless the GNSS type, receiver type/make and data rate (50 or 100 Hz). For the 100 Hz data, the most probable values of the deviation frequency grouped within ~28–40 Hz under quiet condition and shifted to ~37–48 Hz during the weak geomagnetic storms. Additionally, the lower values of deviation frequency of ~18–25 Hz almost disappear from the distribution of the deviation frequencies as it becomes narrower during geomagnetic storms. Considering that the small-scale irregularities shift the deviation frequencies, we can use this indicator as a "red alert" for weakest small-scale irregularities when the deviation frequency reaches ~35–50 Hz. [ABSTRACT FROM AUTHOR]

Ground-based positioning systems (GBPSs) can serve as a supplement and backup to global navigation satellite systems. GBPSs are known for their low cost and high flexibility, but most of them have difficulty in achieving rapid deployment and operation, since the coordinates of transmitters rely on external precise measurements. Several existing self-calibration methods based on carrier phase measurements require known points of GBPS transmitters or receivers, which implies dependence on external measurements. This paper proposes an autonomous coordinate establishment (ACE) method without using known reference points for GBPSs. ACE utilizes a kinematic receiver to collect carrier phase measurements and employs a three-step procedure to establish a regional coordinate system. In the first step, ACE uses the properties of matrix structures to decouple generalized ambiguities and coordinates. Then, ACE obtains the rough estimation of the transmitter coordinates via multi-dimensional scaling in the second step. In the third step, ACE refines the estimate by solving a least squares problem which would be difficult to solve without the previous two steps. Numerical simulations and a real-world experiment show that the coordinate estimation of ACE can achieve decimeter to centimeter-level accuracy. The proposed method enables rapid deployment and operation for GBPSs. [ABSTRACT FROM AUTHOR]

High-sensitivity carrier phase tracking is essential for new GNSS high-precision applications such as unmanned vehicles and smartphones. Increasing coherent integration time is the primary way to improve the sensitivity of carrier phase tracking, which is, however, significantly restricted by the receiver local oscillator instability. We propose a long coherent integration (LCI) architecture to improve carrier phase tracking. The architecture is equipped with a multichannel cooperative loop to track receiver oscillator errors and local loops to perform super-long coherent integration periods. The transfer function of LCI tracking loops is established in s-domain, and the tracking error models induced by thermal noise and Allan deviation oscillator phase noise are derived in z-domain. The performance of the LCI tracking architecture is tested through both simulation and actual GNSS signals. The proposed error models of LCI are validated through the semi-analytic simulation. Both simulation and real signal testing results indicate that LCI tracking loops can perform coherent integration up to 3 s and track extremely weak signals of 6 dB-Hz with carrier phase accuracy of around 4 degrees. [ABSTRACT FROM AUTHOR]

In order to solve the problem of low localization accuracy caused by indoor environment interference in the existing UHF RFID localization methods, an indoor extended Kalman filter (EKF) localization algorithm based on frequency hopping assisted RFID carrier phase was proposed.The virtual large bandwidth obtained by frequency hopping was used for rough distance estimation to realize multipath suppression, and the reliable dual frequency point selection and parameter optimization were completed through the phase after multipath suppression.Finally, EKF algorithm was used to realize high-precision and fast localization.Experimental results show that the average localization error of the proposed algorithm is 9.35 cm, and the real-time performance of the localization solution is nearly 10 times higher than the traditional integer solution method based on Chinese remainder theorem (CRT).

In order to improve the positioning accuracy and the speed of position solution in indoor wireless environment, a high-precision indoor fast positioning algorithm based on carrier phase was proposed.By introducing the reference terminal, the influence of clock error between devices on the accuracy of the positioning algorithm was completely eliminated by using the double difference between the carrier phase measurements of the terminal to be positioned and the reference terminal.Taking advantage of the invariability of integer ambiguity during the phase-locked loop lock-off, an iterative integer ambiguity resolution algorithm based on multi-time point measurement data was designed, and the fast integer ambiguity resolution was realized.After the integer ambiguity was solved, the terminal to be located could be located with high precision by using accurate carrier phase difference measurement.The simulation results show that the positioning algorithm proposed can completely overcome the influence of clock error on positioning performance, and can achieve centimeter-level positioning accuracy at very few sampling time points.

The TurboEdit method is widely used to detect cycle slips on the global navigation satellite system (GNSS) carrier-phase measurements. However, it leads to an increasing number of false alarms in detecting cycle slips under disturbed ionospheric conditions. Besides, once the method detects a cycle slip at one satellite, it treats dual frequencies with cycle slips rather than at one frequency. Considering these two challenges, we developed a solution-based iterative filter detection method to reduce the number of spurious cycle slip detection under disturbed ionospheric conditions. The method initially assumes that there is no cycle slip at each frequency. We then estimate the solutions without cycle slips. A decision of exiting cycle slips is made by examining and comparing the two results solutions with or without cycle slips in terms of usable satellites, ambiguities, and residuals. The uncombined precise point positioning (PPP) during disturbed ionospheric conditions on 17 March 2015 at high latitude was studied to validate the proposed method. Results showed that the detected number of spurious cycle slips was reduced significantly. With fewer marked cycle slips, more stable and smoother positioning performance was achieved when fewer ambiguity parameters were reinitialized. [ABSTRACT FROM AUTHOR]

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GNSS (Global Navigation Satellite System) receivers are not only able to accurately determine position, but also velocity, knowledge of which could be important in several applications. The most adopted technique for velocity estimation exploits the Doppler shift due to the relative motion between the signal source and the receiver. Alternatively, the TDCP (Time-Differenced Carrier Phase) technique, based on the differences between consecutive carrier-phase measurements, can be used. TDCP is theoretically able to achieve better performance compared with the Doppler-based approach, exploiting the high precision of a carrier-phase observable, and without suffering the ambiguity issue. The main objective of this study is to analyze TDCP performance on a smartphone GNSS chip. Smartphones GNSS receivers are usually characterized by noisy observables owing to the low quality of the antenna used; it is, therefore, interesting to compare the smartphone TDCP performance with that of the Doppler-based technique. To evaluate the benefits that TDCP can provide, especially in terms of the smartphone chip, these two approaches to velocity determination are compared using three different devices: a Novatel geodetic receiver, a u-blox multi-frequency receiver, and a Xiaomi Mi8 smartphone. The results demonstrate a performance degradation in the smartphone GNSS chip when TDCP is used, compared with the performance of higher-grade receivers. In fact, the Xiaomi Mi8 maximum errors are greater than those of the Novatel geodetic receiver, but they are still acceptable as they do not exceed 6 cm/s, making the TDCP technique a valid approach for advanced algorithms; indeed, TDCP velocity demonstrates a few mm/s accuracy with a smartphone. The application of a RAIM algorithm enables error reduction and the achievement of reliable information; the obtained solution reliability is about 89%. [ABSTRACT FROM AUTHOR]

A framework that could achieve submeter-level unmanned aerial vehicle (UAV) horizontal navigation in multipath-free environments with cellular carrier phase measurements is developed. This framework exploits the "loose" synchronization between cellular base transceiver station (BTS) clocks. It is shown through extensive experimental data that the beat frequency stability of cellular BTSs approaches that of atomic standards and that the clock deviations can be realized as a stable autoregressive moving average model. This BTS clock model is referred to as loose network synchronization. A rule-of-thumb is established for clustering the clock deviations to minimize the position estimation error, while significantly reducing the computational complexity. The presented models allow the UAV to achieve sustained carrier phase-based meter- to submeter-accurate navigation. To demonstrate the efficacy of the developed framework, this article presents three UAV flight experiments in Southern California, USA, utilizing signals from different cellular providers transmitting at different frequencies. The three experiments took place in open, semiurban environments with nearly multipath-free, line-of-sight (LOS) conditions, in which the UAV traveled 1.72, 3.07, and 0.61 km, achieving a horizontal position root mean squared error of 36.61, 88.58, and 89.33 cm, respectively, with respect to the UAV's on-board navigation system. [ABSTRACT FROM AUTHOR]

Compared with the traditional scalar tracking structure, the vector tracking structure of the satellite navigation receiver has a better signal tracking sensitivity in high dynamic and other situations. However, due to the limited accuracy, it is really hard for a vector tracking loop to maintain the lock of carrier phase. In order to solve this problem, a carrier phase tracking method for vector tracking loops is proposed. First, three common vector tracking structures are analyzed. Second, in the structure of double vector loops, phase compensation is estimated and used to improve the tracking accuracy of the carrier phase. Finally, simulations have been carried out to analyze and verify the feasibility of the proposed scheme. This method estimates and reduces the phase tracking error and has a better tracking effect than the traditional scalar structure. It provides a reference for the implementation of the vector tracking structure and the ultra-tight integrated navigation system. [ABSTRACT FROM AUTHOR]

Today, land and ocean observations are crucial for monitoring climate change. The method of GNSS reflectometry is an opportunistic way to provide low-cost observations of many geophysical parameters. However, although this method has been the subject of numerous research studies, work is still in progress to improve its possibilities and fields of application. This paper focuses on GNSS reflectometry using carrier phase measurements for water altimetry measurements. The difficulties in implementing such a method lie in the need to collect a coherent signal and to solve the integer ambiguity value. In this context, the implementation of innovative signal processing is described, including the correlation of the reflected signals in dedicated software and the prolongation of the coherent integration time to enhance signal coherency. These processes were applied to data collected over Carcans-Hourtin Lake in France to compute the height of the reflection surface which was then compared to in situ GNSS buoy height measurements. The results show that at 300 ft (91.44 m), the differences between the lake heights measured with the buoy and with the reflectometry data can reach less than 1 cm for the L1, E1 and E5 GNSS signals. In addition, the slope of the geoid estimated with the reflectometry data is very consistent with that of the RAF20 geoid model, with a difference of up to less than 2 mm/km.

To solve the problems of low positioning accuracy of traditional positioning algorithm and unsynchronized system clock in indoor wireless environment, a 3D positioning algorithm was proposed based on the fusion of triple-differential carrier phase measurements and time difference of arrival (TDoA) positioning.Considering that the time-varying clock offsets between wireless access points lead to lower positioning accuracy, the measurements from a reference terminal were used to eliminate the influence of time-varying clock offsets.The relative positions were estimated based on triple-differential carrier phase measurements, which were fused with unbiased differential TDoA positioning results to obtain the interim estimated positions.Furthermore, the carrier phase observation equations were linearized by Taylor expansion method, and the high-accuracy positioning was realized by solving the integer ambiguities.Simulation results show that the proposed algorithm eliminates the influence of time-varying clock offsets on positioning performance, and the integer ambiguities are resolved in a short time to achieve high-accuracy positioning.

• Vehicular heading and pitch angles estimation based on dual-GNSS. • Baseline length is investigated as nonlinear constraint to improve the estimation accuracy. • Independent from stationary base station or auxiliary sensor. • Low-cost GNSS receivers/antennas for accurate estimates. This contribution presents a vehicular heading and pitch angles estimation method based on the dual-antenna GNSS scheme, the baseline length is investigated as a priori nonlinear constraint to improve the estimation accuracy. The coordinates of the formed moving baseline are estimated first, the baseline length is exploited to enhance the ambiguity resolution process, and then its corresponding attitude angles are determined. The capability and reliability of the proposed algorithm are assessed by a real car-borne experiment with off-the-shelf, low-cost GNSS receivers. The driving trajectory contains both stationary periods and dynamic situations under the open sky and dense community environments. The experimental results show that, compared to the classical method that does not consider the baseline length constraint, the accuracy improvements of the proposed method on attitude angles range from 16.7% to 84.0% in different observation conditions, and the attitude errors of ambiguity fixed solutions are dominantly less than 5°. [ABSTRACT FROM AUTHOR]

Global Navigation Satellite Systems (GNSS) are used to provide accurate position, navigation, and time (PNT) information to users in various sectors of our society including transportation. Augmentation systems such as differential GNSS (DGNSS), real-time kinematics (RTK), and Precise Point Positioning (PPP) improve the GNSS performance, and providing reliable measurements from its reference station is very crucial. To ensure safe and accurate PNT solutions, code and carrier measurements must be monitored for potential faults or a performance degrade. Although there exist numerous methods to model and monitor the measurements, research on the carrier phase measurements is not as extensive as the code measurements. This paper introduces a split of residuals into receiver noise and multipath components to customize their estimation according to their respective statistical properties. This study also proposes a method to use machine learning-based non-linear regression to effectively model and monitor potential faults in the GNSS measurements including the carrier phase. A training dataset is used to model the nominal quantities of GNSS measurement residuals, and inflation factors are applied to over-bound the fault-free residuals. These inflated residuals are coupled with uncertainty factors to compute thresholds for monitoring carrier phase residuals, and the effectiveness of the thresholds is validated with a test dataset by achieving the false alarm rate of 6.61×10−6, slightly lower than the desired level of 10−5.

The official launch of the Chinese BeiDou Navigation Satellite System with global coverage (BDS-3) presents significant opportunities for various applications, including precision agriculture and autonomous driving, among others. With its global spatial coverage and hybrid space constellation comprising geosynchronous Earth orbit (GEO), inclined geosynchronous orbit (IGSO), and medium Earth orbit (MEO) satellites, BDS can significantly contribute to various GNSS remote sensing applications that require real-time, precise water surface height measurements with high temporal and spatial resolution, such as in tidal monitoring. In this paper, we propose a carrier-phase-based method for BDS Reflectometry (BDS-R) to precisely retrieve real-time water surface height. Firstly, the BDS-R altimetry method is introduced, along with a detailed explanation of the data processing procedures. Secondly, a quality control method tailored to the characteristics of low-cost BDS devices is developed. Thirdly, a land altimetry experiment is conducted to evaluate the precision of BDS-R and analyze the specific contribution of the BDS hybrid constellation. Finally, a water surface altimetry experiment validates the real-time monitoring capabilities for low-cost BDS-R. The results indicate that low-cost BDS-R can achieve real-time centimeter-level water level monitoring with a temporal resolution of 1 s in lakefront environments. The performance of BDS-R can be significantly improved by the BDS hybrid constellation, particularly IGSOs. It is concluded that low-cost BDS-R has great potential for promoting ground-based GNSS remote sensing applications.

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

High-precision position and attitude determination is becoming increasingly important given the surge in BeiDou globalization and 5G commercialization. The most widely employed global navigation satellite system (GNSS) receiver models—specifically, single-difference and double-difference algorithms—can provide reasonable performance and cost for general needs only. Many precision-demanding applications require attitude determination, such as logistics vehicles in transportation and driverless vehicles in cities. They also pursue more sophisticated and cost-effective schemes. This study proposes, for the first time, a novel concept of entanglement difference of carrier phase for the synchronized multi-antenna sets of each GNSS receiver without an inertial navigation system, which is justified by establishing a rigorous mathematical foundation. Moreover, through deliberate experimental design, implementation, and calibration at the system level, this study achieves record higher performances than typical commercial products on the attitude determination precision for the yaw, pitch, and roll angles in both static and dynamic experiments, which demonstrates the strength of this technique and paves the way for its commercialization in the growing GNSS market, especially for China’s BeiDou global networking applications.

Measurements from a geodetic global navigation satellite system (GNSS) setup can be deployed to retrieve geophysics parameters, because coherent reflections from the surrounding environment enter the antenna along with direct signals. Previous GNSS multipath studies of snow depth and sea level were mainly based on signals-to-noise ratio (SNR) measurements. In this article, two new methods based on combinations of pseudorange and carrier phase observations from multi-GNSS dual-frequency signals are proposed, which can be used as substitutes for the SNR method when there are no SNR observations. The first method is based on the combination of dual-frequency pseudorange, which is geometry-free, and avoids any consideration of the influence of ambiguity and cycle slip of carrier phase observations. The second method is based on the combination of dual-frequency pseudorange and carrier phase. This, too, is geometry-free, and is not affected by ionospheric delays. To test these two methods, parameter retrievals using multi-GNSS observations reflected from different surface materials were applied. The derived snow depth series over a 256-day period from SG27 station showed an optimal RMSE of 8 cm with respect to in situ data for both methods by using the combination of observations from GPS L2 and L5 frequency bands. In addition, in a separate 365-day experiment at AT01 station, sea levels were estimated using the proposed methods with optimal RMSE of 21 cm when compared with tide gauge measurements. All these results indicate that the two proposed methods can be seen as supplements to the applications of ground-based multipath reflectometry.

Earth reflected Global Navigation Satellite System (GNSS) signals can be received by dedicated orbital receivers for remote sensing and Earth observation (EO) purposes. Different spaceborne missions have been launched during the past years, most of which can only provide the delay-Doppler map (DDM) of the power of the reflected GNSS signals as their main data products. In addition to the power DDM products, some of these missions have collected a large amount of raw intermediate frequency (IF) data, which are the bit streams of raw signal samples recorded after the analog-to-digital converters (ADCs) and prior to any onboard digital processing. The unprocessed nature of these raw IF data provides an unique opportunity to explore the potential of GNSS Reflectometry (GNSS-R) technique for advanced geophysical applications and future spaceborne missions. To facilitate such explorations, the raw IF data sets from different missions have been processed by Institute of Space Sciences (ICE-CSIC, IEEC), and the corresponding data products, i.e., the complex waveform of the reflected signal, have been generated and released through our public open-data server. These complex waveform data products provide the measurements from different GNSS constellations (e.g., GPS, Galileo and BeiDou), and include both the amplitude and carrier phase information of the reflected GNSS signal at higher sampling rate (e.g., 1000 Hz). To demonstrate these advanced features of the data products, different applications, e.g., inland water detection and surface altimetry, are introduced in this paper. By making these complex waveform data products publicly available, new EO capability of the GNSS-R technique can be further explored by the community. Such early explorations are also relevant to ESA's next GNSS-R mission, HydroGNSS, which will provide similar complex observations operationally and continuously in the future. [ABSTRACT FROM AUTHOR]

Global navigation satellite system (GNSS) plays a vital role in high-precision positioning whereas detecting and mitigating carrier phase multipath error is still a significant challenge. Multipath error is closely related to the users’ environment, so it is difficult to mitigate by traditional differencing techniques. In this paper, we discuss the possibility and potential performance of multipath detection and mitigation with low-cost antennas in real-time kinematic (RTK) positioning. We employ two low-cost antennas and assume that the baseline length is known. We employ the carrier phase, ephemeris, and baseline length to detect the observed and estimated baseline vectors’ consistency in real-time. A reasonable threshold is proposed to detect the satellite signals with the multipath effect, then we eliminate these signals and use the remaining satellite signals for RTK positioning to mitigate multipath. The experiments are carried out in the open environment without multipath and the environment with specular multipath. Experimental results show that the false alarm rate of this method is entirely consistent with the theoretical value. When the number of satellites is six and eight, this method can reduce the RMS (root mean square) of positioning error by approximately 64% and 49%, respectively. At the same time, this method can improve the ambiguity success rate to above 99%. [ABSTRACT FROM AUTHOR]

GNSS receivers are vulnerable to spoofing attacks in which false satellite signals deceive receivers to compute false position and/or time estimates. This work derives and evaluates algorithms that perform spoofing mitigation by utilizing double differences of pseudorange or carrier phase measurements from multiple receivers. The algorithms identify pseudorange and carrier-phase measurements originating from spoofing signals, and omit these from the position and time computation. The algorithms are evaluated with simulated and live-sky meaconing attacks. The simulated spoofing attacks show that mitigation using pseudoranges is possible in these tests when the receivers are separated by five meters or more. At 20 meters, the pseudorange algorithm correctly authenticates six out of seven pseudoranges within 30 seconds in the same simulator tests. Using carrier phase allows mitigation with shorter distances between receivers, but requires better time synchronization between the receivers. Evaluations with live-sky meaconing attacks show the validity of the proposed mitigation algorithms. [ABSTRACT FROM AUTHOR]