Beidou Satellite Research Articles

Co-substituted CuO–ZrO2–Nb2O5 composite ceramics with low-temperature sintering and low-loss for high-performance patch antenna

In the field of microwave dielectric ceramics for patch antennas, it has always been a thorny issue to simultaneously satisfy high dielectric constant, low sintering temperature and low dielectric loss. Here, a CCZN (x = 0.04) composite ceramic with excellent microwave dielectric properties was developed. It can be found that an appropriate amount of Co2+ substitution can enhance the compactness, increase the dielectric constant (εr), reduce the dielectric loss (tanδ) and enhance the temperature coefficient (τf). The composite ceramic with excellent dielectric properties (εr = 22.6, Q × f = 37,624 GHz, τf = −64.9 ppm/°C) shows good sintering compatibility with Ag. Based on this composite ceramic, a high-performance patch antenna was designed for Beidou satellite navigation system (BDS). It presents a small size of 30 × 30*3.8 mm3 and excellent radiation performance (return loss = −32.9 dB, VSWR = 1.047, impedance bandwidth = 60.6 MHz, radiation efficiency = 94.6% and realized gain = 7.704 dB). This work promotes the application of microwave dielectric ceramics in the field of patch antennas.

Study of ionospheric responses over China during September 7–8, 2017 using GPS, Beidou (GEO), and Swarm satellite observations

Study of ionospheric responses over China during September 7–8, 2017 using GPS, Beidou (GEO), and Swarm satellite observations

An orbit maneuver detection method based on orbital elements for BeiDou GEO and IGSO satellites

In addition to the orbital maneuver information, other satellite anomalies were also marked in the satellite’s health status of broadcast ephemeris. For the signal-in-sp ace (SIS) performance evaluation, it is necessary to classify and evaluate the impact of a single fault, as well as the comprehensive impact. Therefore, it remains to identify the satellite orbital maneuver from the broadcast ephemeris and evaluate its impact on the signal-in-space performance. This study proposed an orbit maneuver detection method based on a combination of the square root of the major half-axis of the satellite orbit and the health status of the satellite recorded in broadcast ephemeris. The broadcast ephemerides provided by The Multi-GNSS Experiment (MGEX) from 2016 to 2020 were first used to detect the orbit maneuvers of BeiDou satellites; the orbit maneuvering and recovery periods of GEO and IGSO were detected next. The number of orbital maneuvers of the satellites made each year, and the interval of orbital maneuver of each satellite, was also obtained. The main findings of this study are as follows: (1) the proposed method can detect satellite orbit maneuvers and recovery periods recorded in the broadcast ephemeris; (2) the average orbit maneuvering interval of GEO and IGSO satellites were obtained and found to be approximately 27 days for GEO satellites except C04 and the IGSO, for which they were 45 days and approximately 178 days, respectively; (3) the average recovery time for the two types of satellite orbital maneuvers was about 6.6 h, and generally the same for the BeiDou-3 and BeiDou-2 satellites; and (4) using the detected orbital maneuver intervals and recovery periods, its impact on the signal-in-space availability and continuity of the BeiDou satellite was evaluated, which showed that the per-satellite availability of IGSO satellites were approximately 0.998 and 0.9998/h respectively. The per-satellite availability of each GEO satellite was about 0.986–0.996, and the continuity was about 0.9982/h-0.9992/h; therefore, the orbital maneuver reduced the per-satellite availability and continuity of the GEO and IGSO satellites by 0.002–0.014 and approximately 0.0002/h-0.0018/h, respectively.

FY3E GNOS II GNSS Reflectometry: Mission Review and First Results

FengYun-3E (FY3E), launched on 5 July 2021, is one of China’s polar-orbiting meteorological satellite series. The GNOS II onboard FY3E is an operational GNSS remote sensor that for the first time combines GNSS radio occultation (GNSS RO) and GNSS reflectometry (GNSS-R). It has eight reflection channels that can track eight specular points at the same time, receiving reflected signals from multiple GNSS systems, including GPS, BeiDou and Galileo. The basic GNSS-R output generated by GNOS II is a 122 × 20 non-uniform delay-Doppler map whose high resolution portion captures more information near the specular point. This paper introduces the GNSS-R aspect of the FengYun-3E GNOS II, including the instrument, power calibration and wind speed retrieval algorithm. Preliminary validation results for its first four months of data are also presented. After preliminary quality control, the overall wind speed error is less than 2 m/s at wind speeds below 20 m/s for data from both GPS satellites and BeiDou satellites when compared to the ECMWF reanalysis winds.

Comparative analysis of the performance of Multi-GNSS RTK: A case study in Turkey

The Real Time Kinematic (RTK) method is widely used in the land surveying. Whereas RTK method has the advantage of practical use, positioning accuracy depends mostly on the baseline length due to the atmospheric errors. In general, RTK measurements are made by using GPS and GLONASS satellite systems. For this reason, the positioning performance of the technique is adversely affected under restricted satellite geometry conditions such as urban canyons. At present, most receivers on the market have the ability to track signals of Galileo and BeiDou satellites. Therefore, in this study, the positioning performance of RTK with different satellite combinations (GPS-only, GPS+GLONASS, GPS+GLONASS+GALILEO+BeiDou) was examined with a comparative approach. A field test was carried out considering approximately 20, 40, 60, and 80 km length of baselines. Three different cut off elevation angles – namely, 10°, 20°, and 30° – were chosen for the field test. The results were investigated in terms of accuracy and precision. Also, the ground truth coordinates of the rovers were obtained by post-processing relative method using GAMIT/GLOBK software. The results showed that multi-GNSS combinations provided better repeatability at the 10° cut off angle option. The accuracy of GPS-only solutions varied between 0.63/2.17 cm and 2.40/4.94 cm for horizontal and vertical components, respectively. However, the multi-GNSS combinations did not have a remarkable superiority in terms of position accuracy even at high satellite cut off angle (30°) compared to the GPS-only RTK.

A Simplified Worldwide Ionospheric Model for Satellite Navigation

Ionospheric delay is one of the main sources of error in satellite positioning and navigation. Ionospheric broadcast parameters are required to correct for the ionospheric delay, especially in the case of massive single-frequency users. The well-known Klobuchar model has been providing the ionospheric delay corrections for GPS users during the last several decades. For Galileo users, a three-dimensional electron density model (NeQuick G) based on the NeQuick climatological model is used to correct for ionospheric delay. The recently completed Chinese BeiDou Satellite Navigation System (BDS) broadcasts two types of ionospheric models coefficients on different signals. In this article, we propose a simplified worldwide ionospheric model (SWIM) for satellite positioning. By comparison, our SWIM model has better performance than the Klobuchar model in terms of accuracy at both low and high solar activity, and is comparable to the NeQuick G and BDS ionospheric models. At the same time, the SWIM model has high efficiency because of the simple calculation process. It has great potential for ionospheric delay corrections in satellite navigation and positioning.

Resident Waves in the Ionosphere Before the M6.1 Dali and M7.3 Qinghai Earthquakes of 21–22 May 2021

AbstractGeostationary BeiDou satellites monitor the total electron content (TEC) in the ionosphere over certain locations 24 hr per day without interruption and act as ionosphere‐based seismometers. The system detected perturbations in TEC before both the M6.1 Dali and M7.3 Qinghai earthquakes that occurred during the night of 21–22 May 2021. The TEC perturbations reside mainly over an area within a distance of ∼700 km from the epicenters of the earthquakes. The standing waves revealed the persistence of a subsurface wave source before the occurrences of the earthquakes, which differs from the co‐seismic ionospheric distributions propagating away from the epicenters. The resident waves in TEC and ground vibrations share a frequency of ∼0.004 Hz, which can be attributed to the resonant coupling between the lithosphere and ionosphere.

A Study on Pseudorange Biases in BDS B1I/B3I Signals and the Impacts on Beidou Wide Area Differential Services

Due to satellite signal deformations, there are different constant biases in the same satellite signal that are measured by different technical types of receivers and different satellite signals that are measured by the same type of receiver, which are named pseudorange biases. These biases cannot be transmitted to users with existing navigation parameters, such as satellite time group delay (TGD) and receiver differential code biases (DCB). With the improvement of the signal-in-space accuracy of the Global Navigation Satellite System (GNSS), the pseudorange bias has become one of the primary error sources affecting the accuracy of GNSS services. To ensure the accuracy for users under the wide area differential services (WADS), we extracted the pseudorange biases of Beidou Satellite Navigation System (BDS) B1I, B3I and B1I/B3I signals and analyzed the impact of those biases on users under the WADS. Finally, we tried to eliminate this influence. The results show that the pseudorange biases of the B3I signal are smaller than those of the B1I signal at the centimeter level, but the pseudorange biases of the B1I/B3I signal can reach the meter level. Due to the large pseudorange bias of the B1I/B3I signal, the average user equivalent ranging error (UERE) under the WADS is 1.19 m, which is no better than the average UERE under open services (OS). Influenced by the pseudorange biases, the average positioning accuracies of the B1I/B3I signal are 4.17 m and 4.24 m under the WADS and the OS. When the pseudorange biases are deducted, these accuracies are 3.03 m and 3.50 m, respectively.

In-flight performance analysis of the navigation augmentation payload on LEO communication satellite: a preliminary study on WT01 mission

ABSTRACT With the development of the Low Earth Orbit (LEO) communication constellations, it has become a hot area of research to provide additional navigation augmentation services. Limited by volume, weight, power consumption, and running time, the in-flight performance of navigation augmentation payload remains to be investigated. In this paper, we analyze the data quality of on-board GNSS observation and evaluate the precision of short-arc dynamic Precise Orbit Determination (POD) performance based on the WangTong-01 (WT01) mission. Furthermore, the downlink navigation measurement data of WT01 satellites are analyzed and compared with the GNSS observations. The results show that the average multipath errors of the WT01 on-board GPS L1, L2 and BeiDou Satellite Navigation System (BDS) B1, B2 code observation are 0.54, 0.74, 0.65, and 0.58 m, respectively. The short-arc dynamic POD three-dimensional (3D) overlapping accuracy is 7.1 cm. The average multipath errors of downlink navigation signal Z1 and Z2 are 0.81 and 0.80 m, respectively, which at the same order of magnitude as GNSS signals. The maximum Carrier-to-Noise Ratio (C/N0) value of WT01 downlink measurement data can reach 60 dB Hz, which is much stronger than GNSS and indicates the navigation signals of LEO satellites can meet the basic requirement of navigation augmentation.

Long-Term Frequency Stability Analysis for RRFM and Power-Law Noise Determination of the BeiDou-3 Satellite On-Board Atomic Clocks

The key work this study is the power-law noises determination of 18 BeiDou-3 satellites (PRN19-PRN30 and PRN32-PRN37) on-board atomic clocks. First, for the noise determination of white frequency modulation (WFM), random-walk FM (RWFM), and random-run FM (RRFM), which are the basis of the ensemble timescale filter (ETF), we evaluated the Hadamard deviation with a maximum averaging time up to 30 days. To ensure the reliability of the evaluation, the Hadamard deviation was calculated by the relative clock offset determined from two independent techniques: orbit determination and time synchronization (ODTS) and the intersatellite link (ISL). This work shows that the noise characteristics of the clock offset obtained from ODTS and ISL are different, ODTS clocks are conducive to WFM determination because of low observation noise, and the ISL clocks are conducive to RWFM and RRFM determination because of independent to satellite orbit. Second, the lag 1 and <inline-formula> <tex-math notation="LaTeX">$B1$ </tex-math></inline-formula> bias functions were employed to identify different noises, and the intensities of WFM, RWFM, and RRFM were determined by the Hadamard deviations above. The results of this study indicate that: 1) rubidium clocks (Rbs) always suffer from significant RRFM noise, which improves the magnitude component noise when the averaging time achieves several days; 2) the Rbs of BeiDou-3 satellites have distinctive characteristics of WFM, RWFM, and RRFM, different from the passive hydrogen masers (PHMs), which can only discover the WFM and RWFM noises; and 3) because of the RRFM, when the averaging time is greater than 2e5 s, the Hadamard deviation of Rbs is increased, which causes the frequency stability of Rbs to become an order of magnitude lower than PHMs. Last, simulation analyses and natural Kalman timescale (NKT) constructions using the actual ISL data were employed to verify the effectiveness of noises determination. Through this work, we can almost certainly identify the process noise of ETFs, which can become a reference for ETF construction in the future.

Characterization and Performance Assessment of BeiDou-2 and BeiDou-3 Satellite Group Delays

<h3>Abstract</h3> Based on one year of data, a comprehensive assessment of broadcast group delays and differential code biases (DCBs) from network solutions is presented for all open BeiDou signals. Daily DCB estimates exhibit a precision of 0.1 ns, which also places a limit on long-term variations of the satellite group delays. On the other hand, the estimated DCBs show a notable dependence on the employed receivers, which causes inconsistencies at the few-nanosecond level between BeiDou-2 and BeiDou-3 satellites. Systematic satellite-specific offsets can likewise be identified in broadcast group delay values and clock offsets. These constitute the dominant contribution of the signal-in-space range error (SISRE) budget and are a limiting factor for single point positioning and timing. Use of the modernized B1C/B2a signals is therefore recommended instead of B1I/B3I. This offers a SISRE reduction from about 0.6 m to 0.45 m and also improves the consistency of precise clock and bias products derived from heterogeneous receiver networks.

Mapping of S4 Over the Arabian Peninsula During Solar Minimum

In this letter, we study the temporal and spatial variability of ionospheric irregularities by generating high-resolution maps of the observed amplitude scintillation index (S4) using data from a multi-constellation and multi-frequency GNSS receiver. The study is located in the Arabian Peninsula region, which falls under the northern crest of the equatorial ionization anomaly (EIA). Even though the study was conducted during a solar minimum period, considerable pre-sunset scintillation occurrences have been observed between 15-17 local time, particularly during the winter solstices. While most scintillation occurrences have been observed at low elevation (20 to 25 degrees), a considerable number of scintillation causing ionospheric irregularities have been observed towards the north, east, and southeast of the receiver location, for elevation ranging from 40 to 60 degrees. Out of all the GNSS constellations with medium-earth-orbit (MEO) satellites, GPS was the most impacted by amplitude scintillation, while BeiDou and Galileo satellites were the least affected. It is anticipated that the patches of ionospheric irregularities reported in this work will be further enhanced as solar activity increases in the coming years. Therefore, this work can serve as a reference for future studies during periods of increased geomagnetic activity.

Assessing Repeatable Accuracy Potential of LoRa: A Navigation Approach

Two main classes of radio navigation systems are satellite and ground-based systems. Examples of such systems are eLoran deployed as a terrestrial system, and BeiDou, Galileo, GPS and Quasi-Zenith Satellite System (QZSS) deployed as satellite Navigation Systems. These systems have been investigated in different navigation use-cases using a hybrid receiver capable of receiving any navigation signal. The goal of this paper is to demonstrate LoRa’s capability as a signal of opportunity (SoOP) to be used with other navigation technologies in order to improve repeatable accuracy. While researchers have investigated LoRa’s potential for navigation purposes, there is limited literature regarding the repeatable accuracy estimation using LoRa. Our work proposes using a weighted horizontal dilution of precision (HDOP) while incorporating SNR, spreading factors (SF) and the Ericsson 9999 path loss model. The gateway separation distances: 1500 m, 1000 m and 400 m respectively are employed at a bandwidth of 125kHz to determine repeatable accuracy within a 95% confidence limit. Our simulation results show that for 1500 m, 1000 m, and 400 m, gateway separation distances have a best repeatable accuracy of 1249 m, 284.2 m and 4.314 m, respectively, when the spreading factor (SF) is equal to 12. The initial repeatable accuracy results are promising and comparable to those obtained by other researchers. Our model’s limitation is that the best SNR was not used to determine position. A climatic model and stochastic channel interference observed in the 900MHz frequency band were also assumed to be negligible to provide a working model that can be modified as data becomes available.

Ground GNSS Station Selection to Generate the Global Ionosphere Maps Using the Information Content

AbstractMore and more satellite constellations and ground receivers are available all over the world, and they can provide rich ionospheric remote sensing data sources. Due to the fact that different analysis centers use different generation techniques and different ground stations, their routinely released Global Ionosphere Maps (GIMs) have some differences. To study the problems of how many stations and which stations should be optimally chosen to generate the GIMs, a step‐by‐step iterative method based on the information content is proposed under the framework of 3DVAR data assimilation. This method adopts the information content to qualitatively evaluate the information contribution of a measurement to the reconstructed GIM, and selects the ground station with a maximum information content in every iteration. About 500 ground receivers from the International GNSS Services networks and Multi‐GNSS Experiment networks are collected from DOY 001 to DOY 120 in 2018 to demonstrate the feasibility of this method. The results show that the information contribution from the first 100 selected stations is over 70%, and the information contribution from the first 200 chosen stations is up to 87%. When the station selection criterion is taken as 95% of the total information content, nearly 300 stations are needed to reconstruct each GIM. Moreover, the quantitative information contribution from GPS, GLONASS, GALILEO, and BEIDOU satellite constellations is preliminarily analyzed.

Navigator Notes

Welcome to the Fall 2022 issue of NAVIGATION . In this issue, we again feature articles on a wide range of topics including the instrumentation group delays of BeiDou satellites, the gain patterns of GPS satellite antennas, time transfer for a lunar navigation system, and several articles on

Linear Spline and CNN-LSTM for Missing Values Imputation of Beidou Satellite Radiation Dose Data

Linear Spline and CNN-LSTM for Missing Values Imputation of Beidou Satellite Radiation Dose Data

Error Handling Method for Improving BDS Monitoring Accuracy of Bridge Deformation

The existing high‐tech bridge deformation monitoring technologies mostly use the GPS system. To eliminate the dependence on this system, China has independently developed and built the Beidou satellite navigation system. In this study, an improved algorithm for differently modulated signals is proposed to increase the accuracy of satellite monitoring and minimise the intercode interference into the output signals of the Beidou bridge deformation monitoring system. It includes a modified recurrent least square constant modulus algorithm (RLS‐CMA) developed using MATLAB software. The numbers of iterations for four modulated signals are determined through various blind equalisation and intersymbol interference (ISI) algorithms as well as by performing error vector magnitude comparison simulations without equalisation, with CMA equalisation, and with enhanced RLS‐CMA equalisation. At high signal‐to‐noise ratios, the correction speed and anti‐intercode interference capability of the improved RLS‐CMA are greater than those of the CMA. Moreover, the lower the error vector amplitude, the higher is the accuracy of received constellations. The error vector amplitude achieved by the RLS‐CMA equalisation algorithm is lower than those of the CMA equalisation and nonequalisation algorithms, while its accuracy is increased by 17%. Hence, the improved RLS‐CMA can eliminate ISI, increase the accuracy of satellite monitoring, and satisfy the requirements of theoretical analysis, calculation accuracy, and engineering error.

Characterization and Calibration of Spaceborne GNSS-R Observations Over the Ocean From Different BeiDou Satellite Types

The Global Navigation Satellite System Reflectometry (GNSS-R) technique can measure ocean surface winds and other geophysical parameters from forward scattered GNSS (GPS, BeiDou, Galileo, etc.) signals. However, most early spaceborne missions only captured GPS signals while the study of spaceborne reflectometry using BeiDou signals (BDS-R) is limited. The GNOS-II payload onboard China’s FY-3E satellite has been operationally collecting a large number of BDS-R data since July 10, 2021. BDS is different from GPS in the orbit, signal frequency, chipping rate and Effective Isotropic Radiated Power (EIRP). Furthermore, BDS satellites have different generations and orbits. This paper, for the first time, comprehensively characterizes the spaceborne BDS-R observations over the ocean using the FY-3E GNOS-II data from different BDS satellite types including BDS-2 IGSO, BDS-2 MEO, BDS-3 IGSO and BDS-3 MEO. Their spatial coverage, spatial resolution, effective scattering area, incidence angle, range corrected gain, EIRP and signal-to-noise ratio have been analyzed and compared to those of GPS-R. Spaceborne BDS-R shows a lot of uniquenesses compared to GPS-R. The BDS-R observables are then calibrated separately for each type. An intercalibration is also applied to correct extra calibration errors. After the calibration, BDS-R observables and retrieved winds are consistent between each type and compared to those of GPS-R. Calibrated observables from FY-3E GNOS-II are also evaluated by comparing them to those measured by the Cyclone Global Navigation Satellite System (CYGNSS) mission and a theoretical model. The results of this paper can provide a reference for future BDS-R studies and spaceborne GNSS-R mission design.

Optimal GNSS-Based Passive SAR Large Field-of-View Imaging via Multistatic Configuration: Method and Experimental Validation

In terms of the global coverage provided by global navigation satellite system (GNSS) signals, radar images of a large field-of-view can be obtained via passive synthetic aperture radar (SAR) using these signals of opportunity. Usually, large field-of-view imaging is challenging using conventional SAR methods owing to the space-variant resolution. In addition, only a moderate range resolution can be provided by the GNSS transmitters in the passive SAR system. In this paper, an optimal imaging method for a large field-of-view using GNSS-based passive SAR is proposed, which exploits the inherent multistatic nature of GNSS. At first, the spatial resolution of each scatterer in the observation area relative to each GNSS transmitter is calculated according to the geometry. Then, the selection of the transmitter set is modeled as an optimization problem, where the minimal resolution cell is used as the optimal criterion. After that, an evolutionary algorithm is applied to solve the optimization problem. Finally, the space-time combination of the echoes over a long dwell time concerning selected GNSS transmitters is performed to form the radar image with a minimal spatial resolution. The proposed method is extensively validated using two experimental datasets, where the passive radar consists of BeiDou satellites and a fixed receiver. The spatial resolution improvement and the large field-of-view imaging capability of the proposed method are forcefully demonstrated according to the experimental results.

An optimization method of clock synchronization for large-scale regional power network based on IEEE 1588

At present, mobile devices generally use GPS, Beidou and other satellite time service methods to obtain time, but the clock synchronization based on IEEE 1588 protocol still has deviation. To solve this problem, a clock synchronization method is proposed to improve IEEE 1588 protocol. Based on the analysis of IEEE 1588 protocol, the clock deviation and frequency deviation which affect the synchronization accuracy are modeled. The second-order Kalman filtering algorithm is used to recursively deduce the clock deviation and frequency deviation, and the Allan variance is used to verify the noise characteristics and constantly correct the clock deviation. Finally, the improved effect is verified by relevant experiments. The results show that the improved system can improve the synchronization accuracy.