Evaluation of BDS Time Transfer on Multiple Baselines for UTC

Extension of the BDS IGSO and MEO satellite antenna patterns with FengYun-3C and LuTan-1 onboard data

The BeiDou Navigation Satellite System (BDS) precise point positioning (PPP) service, PPP-B2b, is broadcasted by BDS-3 geostationary earth orbit (GEO) satellites, which provides high-precision positioning and timing services to users in China and neighboring regions. This paper presents an analysis of real-time PPP time transfer experiments utilizing PPP-B2b corrections from BDS-3 satellites and compares the results with real-time time transfer performance based on the state space representation (SSR) corrections broadcast by the International Global Navigation Satellite System Service Data Center of Wuhan University. PPP-B2b/SSR corrections were applied to the broadcast ephemeris to derive precise satellite positions and clock biases. The BDS-3 B1I + B3I and B1C + B2a combinations were analyzed under short baseline conditions using real-time PPP processing software. The results demonstrated that the standard deviation (STD) of real-time PPP time transfer for the B1C + B2a dual-frequency combination of BDS-3 using PPP-B2b/SSR corrections were consistently below 0.2 ns, while the STD for the B1I + B3I dual-frequency combination remained under 0.3 ns. The 10 000 s Allan Deviations for all combinations were better than 1.322 × 10−14. The findings confirmed that the PPP-B2b of BDS-3 is capable of achieving sub-nanosecond time transfer, comparable to SSR-based methods. PPP-B2b is more accessible and offers a broader range of applications compared to SSR, making it suitable for long-term, reliable real-time time transfer operations in network-restricted environments.

In-orbit performance of GNOS on-board FY3-C and the enhancements for FY3-D satellite

With the rapid development of the Beidou satellite navigation system (BDS), assessment of its signal quality and navigation performance becomes more and more important. The pseudo-range multipath, carrier-phase signal-to-noise ratio (SNR) and accuracy of standard point positioning are usually taken as the indicators for assessment. In this research, we compared the signal quality and navigation performance of BDS with other three Global Navigation Satellite System (GPS, GLONASS, Galileo). The results of the Asia-Pacific region show that the pseudo-range multipath error for BDS is similar with GPS whereas the GLONASS code measurements exhibit a higher level. The level of carrier-phase signal-to-noise ratio for Galileo is largest, but similar for BDS, GPS and GLONASS. The standard point navigation and positioning performance of BDS is slightly lower than GPS, but it is better than GLONASS, and the accuracy of BDS, GPS and GLONASS standard point positioning is about 10 m. The pseudo-range multipath error of BDS increases as the satellites elevation decreases, but the carrier-phase signal-to-noise ratio is opposite. The variation of pseudo-range multipath error of BDS GEO satellites is small except for low satellites elevation, but the variation of signal-to-noise ratio of GEO satellites is relatively stable. The variation of multipath and signal-to-noise ratio of BDS IGSO and MEO satellites is relatively stable when the satellites elevation is larger than a certain value.

Because of the special design of BeiDou navigation satellite system (BDS) constellation, the effects of ionospheric scintillation on operational BDS generally are more serious than on the global positioning system (GPS). As BDS is currently providing global services, it is increasingly important to seek strategies to mitigate the scintillation effects on BDS navigation and positioning services. In this study, an improved cycle-slip threshold model is proposed to decrease the high false-alarm rate of cycle-slips under scintillation conditions, thus avoiding the frequent unnecessary ambiguity resets in BDS precise point positioning (PPP) solution. We use one-year (from 23 March 2015 to 23 March 2016) BDS dataset from Hong Kong Sha Tin (HKST) station (22.4°N, 114.2°E; geomagnetic latitude: 15.4°N) to model the cycle-slip threshold and try to make it suitable for three types of BDS satellites and multiple scintillation levels. The availability of our mitigation strategy is validated by using three months (from 1 September 2015 to 30 November 2015) BDS dataset collected at 10 global navigation satellite system (GNSS) stations in Hong Kong. Positioning results demonstrate that our mitigated BDS PPP can prevent the sudden fluctuations of positioning errors induced by the ionospheric scintillation. Statistical results of BDS PPP experiments show that the mitigated solution can maintain an accuracy of about 0.08 m and 0.10 m in the horizontal and vertical components, respectively. Compared with standard BDS PPP, the accuracy of mitigated PPP can be improved by approximately 24.1%, 38.2%, and 47.9% in the east, north, and up directions, respectively. Our study demonstrates that considering different scintillation levels to establish appropriate cycle-slip threshold model in PPP processing can efficiently mitigate the ionospheric scintillation effects on BDS PPP.

The code-phase divergences, which are minimal for GPS, GLONASS, and Galileo satellites, are commonly found in BeiDou Navigation Satellite System (BDS) Geostationary Orbit (GEO), Inclined GeoSynchronous Orbit (IGSO) and Medium Earth Orbit (MEO) satellites. Several precise positioning applications which use code observations are severely affected by these code biases. We present an analysis of code bias based on multipath (MP) combination observations. To mitigate the effect of BDS code bias on precise positioning, we proposed a periodical correction method using a low-pass filter for BDS GEO, IGSO and MEO satellites. The auto-correlation of MP series over long periods is analyzed to obtain the periods of the dominant repeating components for three types of BDS satellites. The periods of the dominant daily repeating components are close to 86,160 s for BDS GEO and IGSO satellites while 603,120 s for MEO satellites. The zero phase-shift low-pass filter was used to extract the low-frequency components of MP series and then low-frequency components are applied to mitigate the code bias periodically. The developed correction methods can make a more remarkable improvement for the accuracy of MP series, compared to the current elevation-dependent correction models. Data sets collected at 50 Global Navigation Satellite System (GNSS) ground stations including 15 of the International GNSS Monitoring and Assessment System (iGMAS) and 35 of the Multi-GNSS Experiment (MGEX) stations are employed for this study. To analyze the influence of code bias on precise positioning and validate the effectiveness of the correction methods, some applications such as single point positioning (SPP), wide-lane (WL) ambiguity analysis and Uncalibrated Phase Delays (UPDs) estimation are conducted. After applying the proposal correction method to the code observations, SPP solutions outperform the uncorrected ones in term of positioning accuracy. The positioning accuracy decreased by 0.28 and 0.1 m in the north and east components and the improvements are more significant for the U components decreased by 0.42 m. In addition, the systematic variations of Melbourne-Wübbena (MW) combination are greatly removed and the convergence time of the MW series are decreased. Moreover, significant improvement is also achieved in terms of the usage rate and residuals of UPDs estimation.

Satellites of the third generation BeiDou Navigation Satellite System (BDS) will be equipped with Ka-band antennas and communicate through point-to-point Inter-Satellite Links (ISLs). Link assignment and routing algorithms of other Global Navigation Satellite Systems (GNSSs) are not suitable for BDS ISL due to its unique communication system. This article mainly focuses on inter-satellite link assignment and routing problem in BDS ISL network which is a new challenge and has no mature algorithm proposed specially for it before. Firstly, time slot matrix assigning algorithm is put forward to solve link assignment problem based on characteristic of BDS ISL. Performance of this algorithm is simulated and ISL network topology designed by this algorithm is proved to be good in aspects of average number of links, average position dilution of precision (PDOP) and other important indicators. Secondly, on the basis of determined network topology, this paper provides a heuristic route planning strategy for information transmission in BDS ISL network. Path Combinational Optimization algorithm based on Simulated Annealing (PCO-SA) is proposed and elaborated in this paper. By combining PCO-SA and adjusted Contact Graph Routing (CGR) algorithm, a common solution for routing problem of navigation related data can be achieved. Simulation results compared with other route planning methods show that PCO-SA can not only significantly increase success ratio of route planning, but also optimize average time delay and hop of planned path.

Abstract. The differential code bias (DCB) of the Global Navigation Satellite System (GNSS) is an important error source in ionospheric modeling, which was generally estimated as constants every day. However, the receiver DCB may be changing due to the varying spatial environments and temperatures. In this paper, a method based on the global ionospheric map (GIM) of the Center for Orbit Determination in Europe (CODE) is presented to estimate the BeiDou Navigation Satellite System (BDS) receiver DCB with epoch-by-epoch estimates. The BDS receiver DCBs are analyzed from 30 d of Multi-GNSS Experiment observations. The comparison of estimated receiver DCB of BDS with the DCB provided by the German Aerospace Center (DLR) and the Chinese Academy of Sciences (CAS) shows a good agreement. The root-mean-square (rms) values of receiver DCB are 0.43 and 0.80 ns with respect to the DLR and CAS estimates, respectively. In terms of the intraday variability of receiver DCB, most of the receiver DCBs show relative stability within 1 d with the intraday standard deviation (SD) of less than 1 ns. However, larger fluctuations with more than 2 ns of intraday receiver DCB are found. Besides, the intraday stability of receiver DCB calculated by the third-generation BDS (BDS-3) and the second-generation BDS (BDS-2) observations is compared. The result shows that the intraday stability of BDS-3 receiver DCB is better than that of BDS-2 receiver DCB.

It is foreseeable that the BeiDou navigation satellite system with global coverage (BDS-3) and the BeiDou navigation satellite (regional) system (BDS-2) will coexist in the next decade. Care should be taken to minimize the adverse impact of the receiver-related biases, including inter-system biases (ISBs), differential code biases (DCB), and differential phase biases (DPB) on the positioning, navigation, and timing (PNT) provided by global navigation satellite systems (GNSS). Therefore, it is important to ascertain the intrinsic characteristics of receiver-related biases, especially in the context of the combination of BDS-3 and BDS-2, which have some differences in their signal level. We present a method that enables time-wise retrieval of between-receiver ISBs, DCB, and DPB from multi-frequency multi-GNSS observations. With this method, the time-wise estimates of the receiver-related biases between BDS-3 and BDS-2 are determined using all five frequencies available in different receiver pairs. Three major findings are suggested based on our test results. First, code ISBs are significant on the two overlapping frequencies B1II and B2b/B2I between BDS-3 and BDS-2 for a baseline with non-identical receiver pairs, which disrupts the compatibility of the two constellations. Second, epoch-wise DCB estimates of the same type in BDS-3 and BDS-2 can show noticeable differences. Thus, it is unreasonable to treat them as one constellation in PNT applications. Third, the DPB of BDS-3 and BDS-2 may have significant short-term variations, which can be attributed to, on the one hand, receivers composing baselines, and on the other hand, frequencies.

As a global navigation satellite system, BeiDou Navigation Satellite System (BDS) is independently established by China and aimed to serve the whole world. Since its formal regional service provision on December 27 2012, BDS has maintained continuous and stable operation, and the service performance has met with the specification requirements. Meanwhile, the BDS application development activities have been proceeded smoothly. BDS have been using in high-precision positioning, survey and mapping, disaster prevention and mitigation, fleet management, maritime applications, precision agriculture, etc. This presentation will provide an overview of the current status of the BDS application development.

The utilization of Global Navigation Satellite System (GNSS) is becoming an attractive navigation approach for geostationary orbit (GEO) satellites. A high-sensitivity receiver compatible with Global Position System (GPS) developed by the United States and BeiDou Navigation Satellite System (BDS) developed by China has been used in a GEO satellite named TJS-5 to demonstrate feasibility of real-time navigation. According to inflight data, the GNSS signal characteristics including availability, position dilution of precision (PDOP), carrier-to-noise ratio (C/N0), observations quantity and accuracy are analyzed. The mean number of GPS and GPS + BDS satellites tracked are 7.4 and 11.7 and the mean PDOP of GPS and GPS + BDS are 10.24 and 3.91, respectively. The use of BDS significantly increases the number of available navigation satellites and improves the PDOP. The number of observations with respect to C/N0 is illustrated in detail. The standard deviation of the pseudorange noises are less than 4 m, and the corresponding carrier phase noises are mostly less than 8 mm. We present the navigation performance using only GPS observations and GPS + BDS observations combination at different weights through comparisons with the precision reference orbits. When GPS combined with BDS observations, the root mean square (RMS) of the single-epoch least square position accuracy can improve from 32.1 m to 16.5 m and the corresponding velocity accuracy can improve from 0.238 m/s to 0.165 m/s. The RMS of real-time orbit determination position accuracy is 5.55 m and the corresponding velocity accuracy is 0.697 mm/s when using GPS and BDS combinations. Especially, the position accuracy in x-axis direction reduced from 7.24 m to 4.09 m when combined GPS with BDS observations.

Using Global Navigation Satellite System (GNSS) signals of BeiDou navigation satellite system (BDS) and global position system (GPS) for soil moisture estimation is an emerging technology in microwave remote sensing since soil moisture is an important index in regional water cycle research. Based on the developed forward multipath model, this study first investigates the feasibility of soil moisture estimation based on GNSS interference signals; then compares the difference between the Signal-to-Ratio (SNR) data and the signal strength (sn_rnx) data from GPS. After that, this paper analyzes the experimental data from BDS receivers and CORS stations. The analyzed results show that both fitted phase of BDS SNR data and GPS sn_rnx data will increase when the soil moisture increases, and the phase will decrease when soil moisture decreases, and the method of using sn_rnx data can obtain the change trend of soil moisture and can be used as an alternative to solve the problem that the SNR data is unavailable in many GNSS data sets.

The differential code bias (DCB) in Global Navigation Satellite System (GNSS) satellites should be precisely determined using real ground GNSS data when designing certain applications, such as precise positioning, navigation and timing. This paper analyzed the relationship between satellite elevation angle with DSNR (difference signal to noise ratio) of BDS (BeiDou Navigation Satellite System) different orbital satellite. The experimental results showed that the DSNR of IGSO satellite was less than 5dBHz and more stable, much better than the other satellites; the change of GEO satellite DSNR was small, but the absolute value was large; MEO satellite DSNR changed frequently and big. A new algorithm to get the BDS observation weight is introduced by considering the distance between the satellite and the Earth and DSNR. The results indicated that the new weight algorithm improved the DCB accuracy and enhanced the stabilities, which improved GEO satellites 1–15 %, IGSO satellites 4.5–16 %, MEO satellites 20–22 %.

The R2CGGTTS software tool developed at the Royal Observatory of Belgium (ROB) to provide clock solutions in the standard Common GNSS Generic Time Transfer Standard (CGGTTS) has been extended to BeiDou Navigation Satellite System (BDS). The BDS includes satellites in three different orbits: 1)Medium Earth Orbit (MEO); 2)Inclined Geosynchronous Satellite Orbit (IGSO); and 3)Geostationary Earth Orbit (GEO). This paper presents first results obtained with this upgraded software, and a comparison between common view (CV) time transfer solutions obtained with either BDS, or GPS or Galileo. These preliminary results indicate that the BeiDou MEO satellites give time transfer results with a higher noise than the GPS results. This additional noise is shown to be due to some elevation-dependent delay in the BDS code measurements. Some biases were furthermore pointed out between the CV results obtained with the different BeiDou MEO satellites when the receivers used in the two stations are of different make. These biases may reach some nanoseconds, and find most probably their origin in the receiver hardware or firmware. It is shown additionally that using the BeiDou IGSO satellites and the GEO satellites, although increasing the number of observations, especially in the Asia-Pacific region, introduces a significant time transfer noise in the CV results.

The improvement of BDS Observation Geometry with LEO constellations in Orbit Determination