A new precise point positioning (PPP)-B2b augmentation service broadcast by the BeiDou Navigation Satellite System (BDS-3) geosynchronous Earth orbit (GEO) satellite can provide real-time and ...high-precision orbit and clock offset corrections for global navigation satellite system (GNSS) users in China and its surrounding areas. It has great significance and research value for real-time and high-precision positioning applications. First, orbit, clock offset, and differential code bias (DCB) of PPP-B2b products are evaluated. Second, the influence of PPP-B2b service on the enhanced positioning of single-frequency (SF), dual-frequency (DF), and Multi-Frequency (MF) real-time PPP using 30 days of BDS-3 observations is verified. The result shows that the standard deviation (STD) of clock offset and the root mean square (rms) of orbit in the 3-D direction for medium Earth orbit (MEO) satellites are 0.118 ns and 0.286 m, respectively, which is 75.9% and 18.3% higher than that of broadcast ephemeris. The statistical results show that the median positioning accuracy of static SF PPP, DF PPP, and MF PPP is better than 0.20/0.09/0.08 m, and the convergence time is better than 51/10/8 min. The median positioning accuracy of kinematic SF PPP, DF PPP, and MF PPP is better than 0.40/0.12/0.12 m, and the convergence time is better than 145/16/12 min. Using the PPP-B2b products, the positioning accuracy of DF PPP and MF PPP is comparable and close to that of DF PPP using the precise products, while the convergence time of MF PPP is improved by 24.8% and 27.7% over DF PPP in static and kinematic solutions, respectively.
Equipped with inter-satellite links (ISLs), BeiDou-3 satellites are able to operate autonomously in case of ground facility malfunction. To provide reliable positioning, navigation and timing service ...during autonomous operation, satellites need to maintain a stable time reference. In this letter, we propose a minimal covariance distributed Kalman filter (MCDKF) to realize distributed timekeeping. The proposed algorithm overcomes the problem of network dynamics. Meanwhile, it improves the stability of the on-board time reference by minimizing the variance of the estimate errors at each update step, under the constraint of local observations. Simulation results show that the proposed algorithm reduces the estimation variance and improves the frequency stability compared to other distributed algorithms.
This study validated and investigated elevation- and frequency-dependent systematic biases observed in ground-based code measurements of the Chinese BeiDou navigation satellite system, using the ...onboard BeiDou code measurement data from the Chinese meteorological satellite Fengyun-3C. Particularly for geostationary earth orbit satellites, sky-view coverage can be achieved over the entire elevation and azimuth angle ranges with the available onboard tracking data, which is more favorable to modeling code biases. Apart from the BeiDou-satellite-induced biases, the onboard BeiDou code multipath effects also indicate pronounced near-field systematic biases that depend only on signal frequency and the line-of-sight directions. To correct these biases, we developed a proposed code correction model by estimating the BeiDou-satellite-induced biases as linear piece-wise functions in different satellite groups and the near-field systematic biases in a grid approach. To validate the code bias model, we carried out orbit determination using single-frequency BeiDou data with and without code bias corrections applied. Orbit precision statistics indicate that those code biases can seriously degrade single-frequency orbit determination. After the correction model was applied, the orbit position errors, 3D root mean square, were reduced from 150.6 to 56.3 cm.
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GNSS single-epoch real-time kinematic (RTK) positioning depends on correct ambiguity resolution. If the number of observed satellites in a single epoch is insufficient, which often happens with a ...standalone GNSS system, the ambiguity resolution is difficult to achieve. China’s BeiDou Navigation Satellite System has been providing continuous passive positioning, navigation and timing services since December 27, 2012, covering China and the surrounding area. This new system will increase the number of satellites in view and will have a significant effect on successful ambiguity resolution. Since the BeiDou system is similar to GPS, the procedure of data processing is easier than that for the Russian GLONASS system. We briefly introduce the time and the coordinate system of BeiDou and also the BeiDou satellite visibility in China, followed by the discussion on the combined GPS/BeiDou single-epoch algorithm. Experiments were conducted and are presented here, in which the GPS/BeiDou dual-frequency static data were collected in Wuhan with the baseline distance varying from 5 to 13 km, and processed in separate and combined modes. The results indicate that, compared to a standalone GPS or BeiDou system, the combined GNSS system can increase the successful ambiguity fixing rate for single epochs and can also improve the precision of short baselines determination.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In this contribution, we present a GPS+GLONASS+BeiDou+Galileo four-system model to fully exploit the observations of all these four navigation satellite systems for real-time precise orbit ...determination, clock estimation and positioning. A rigorous multi-GNSS analysis is performed to achieve the best possible consistency by processing the observations from different GNSS together in one common parameter estimation procedure. Meanwhile, an efficient multi-GNSS real-time precise positioning service system is designed and demonstrated by using the multi-GNSS Experiment, BeiDou Experimental Tracking Network, and International GNSS Service networks including stations all over the world. The statistical analysis of the 6-h predicted orbits show that the radial and cross root mean square (RMS) values are smaller than 10 cm for BeiDou and Galileo, and smaller than 5 cm for both GLONASS and GPS satellites, respectively. The RMS values of the clock differences between real-time and batch-processed solutions for GPS satellites are about 0.10 ns, while the RMS values for BeiDou, Galileo and GLONASS are 0.13, 0.13 and 0.14 ns, respectively. The addition of the BeiDou, Galileo and GLONASS systems to the standard GPS-only processing, reduces the convergence time almost by 70 %, while the positioning accuracy is improved by about 25 %. Some outliers in the GPS-only solutions vanish when multi-GNSS observations are processed simultaneous. The availability and reliability of GPS precise positioning decrease dramatically as the elevation cutoff increases. However, the accuracy of multi-GNSS precise point positioning (PPP) is hardly decreased and few centimeter are still achievable in the horizontal components even with 40
∘
elevation cutoff. At 30
∘
and 40
∘
elevation cutoffs, the availability rates of GPS-only solution drop significantly to only around 70 and 40 %, respectively. However, multi-GNSS PPP can provide precise position estimates continuously (availability rate is more than 99.5 %) even up to 40
∘
elevation cutoff (e.g., in urban canyons).
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Ultra-fast satellite clock bias (SCB) products play an important role in real-time precise point positioning. Considering the low accuracy of ultra-fast SCB, which is unable to meet the requirements ...of precise point position, in this paper, we propose a sparrow search algorithm to optimize the extreme learning machine (SSA-ELM) algorithm in order to improve the performance of SCB prediction in the Beidou satellite navigation system (BDS). By using the sparrow search algorithm's strong global search and fast convergence ability, we further improve the prediction accuracy of SCB of the extreme learning machine. This study uses ultra-fast SCB data from the international GNSS monitoring assessment system (iGMAS) to perform experiments. First, the second difference method is used to evaluate the accuracy and stability of the used data, demonstrating that the accuracy between observed data (ISUO) and predicted data (ISUP) of the ultra-fast clock (ISU) products is optimal. Moreover, the accuracy and stability of the new rubidium (Rb-II) clock and hydrogen (PHM) clock onboard BDS-3 are superior to those of BDS-2, and the choice of different reference clocks affects the accuracy of SCB. Then, SSA-ELM, quadratic polynomial (QP), and a grey model (GM) are used for SCB prediction, and the results are compared with ISUP data. The results show that when predicting 3 and 6 h based on 12 h of SCB data, the SSA-ELM model improves the prediction model by ~60.42%, 5.46%, and 57.59% and 72.27%, 44.65%, and 62.96% as compared with the ISUP, QP, and GM models, respectively. When predicting 6 h based on 12 h of SCB data, the SSA-ELM model improves the prediction model by ~53.16% and 52.09% and by 40.66% and 46.38% compared to the QP and GM models, respectively. Finally, multiday data are used for 6 h SCB prediction. The results show that the SSA-ELM model improves the prediction model by more than 25% compared to the ISUP, QP, and GM models. In addition, the prediction accuracy of the BDS-3 satellite is better than that of the BDS-2 satellite.
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The single-frequency (SF) BeiDou satellite-based augmentation system (BDSBAS) has been broadcasting small ionospheric residual uncertainties and grid ionospheric vertical errors (GIVEs), which may ...cause events of ionospheric integrity or system integrity. The system availability at high latitudes over Chinese territory is also constrained by the conventional interpolation algorithm within the ionosphere map surrounded by ionospheric grid points (IGPs). In this article, we proposed an airborne ionospheric correction approach based on the combination of a residual uncertainty model, a GIVE inflation strategy, and a global interpolation algorithm, and developed and verified with data from January 2021 to June 2022. The uncertainty model was rebuilt using the broadcast information from BDSBAS and the global ionosphere map (GIM) from the Center for Orbit Determination in Europe (CODE). From this model and historical residual data, we obtained the inflated GIVE that increased the average envelope probability of ionospheric residual errors from 94.08% to 99.99% for 117 BDSBAS IGPs. The biharmonic spline method (BSM) based on Green functions was introduced to extend the original ionosphere map to the north by 10° to enable more augmented signals. BSM increased the interpolation accuracy of the user ionospheric vertical delay (UIVD) by about 63%. The results from the regional test proved that our proposed approach could obtain an average minimum ionospheric safety index of 6.27 within the extended ionosphere map and increase the average coverage rate in the Chinese mainland from 95.15% to 99.07%. In the static station tests and the dynamic flight tests, positioning accuracies increased or remained the same, while misleading information (MI) events could be avoided.
Precipitable water vapour (PWV) is a primary factor that affects climate and weather. The accurate retrieval of PWV is crucial for weather prediction and meteorological research. Interferometric ...Synthetic Aperture Radar (InSAR) has been rapidly developed in recent years and proven effective in PWV retrieval in the regions of good coherence. However, there are large areas of natural terrain where signals decoherence that limit the precision of PWV retrieval. Besides, due to the differential interference processing of InSAR data, the results of its retrieval are differential PWV (ΔPWV). In this study, the StaMPS-InSAR was used to overcome the problem of weak detection ability in low coherence regions. A series of 11 Sentinel-1A images were selected to retrieve space-continuous ΔPWV. Beidou Satellite Navigation System (BDS) can retrieve high-precision PWV. Hence, the BDS data was utilized to convert the InSAR-derived ΔPWV to PWV. Compared with the BDS-derived PWV, the root mean square error (RMSE) of the experimental results is 1.3 mm with a spatial resolution as fine as 20 m. The correlation coefficient between the deviations and Liquid Cloud Water is 0.65, indicating a positive correlation. We demonstrate the advantage of the proposed method for retrieving PWV in computational efficiency by comparing it with the SBAS-InSAR. With the increasing stack size of the SAR images, our method can reduce the taking time for processing. The proportion can reach 12.6% when the stack size of SAR images is 20. By the spatio-temporal analysis of the results, we found some characteristics of PWV in mountain areas especially. The results have certain reference value for the space-continuous PWV retrieval and the study of PWV spatio-temporal characteristics.
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Obtaining voyage data through a vessel monitoring system (VMS) and transmitting it to a remote monitoring center through satellites is an important link to realize the information perception of smart ...ships. However, improving data quality to ensure the integrity of information is still an open question. Taking into account the complex and harsh marine environment, a BeiDou satellite transmission link will inevitably suffer the challenge of packet loss. Therefore, this paper proposes a novel BeiDou satellite transmission framework with missing package imputation to improve the information perception ability of smart ships. In particular, we propose a two-stage missing packet imputation strategy (T-MPI). First, a bidirectional recurrent neural network (Bi-RNN) based on temporal view imputation is designed to learn the time correlation of the data. Second, considering the attributive view imputation of multivariate data, an autoencoder with a linear aggregation module (LA-AE) is proposed to capture sudden changes in the ship's complex sailing state. An experimental platform was established to verify the developed framework, and real freighter transportation data were used to prove the effectiveness of our proposed imputation strategy under complex sailing conditions.
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