Number Of Visible Satellites Research Articles

The Positioning Accuracy and Performance Simulation Analysis of BeiDou-3 in Cote d’Ivoire

BeiDou Navigation Satellite System will operate world widely in 2020. Therefore, it is very important to master the accuracy and positioning performance of BeiDou-3 in West Africa. The number of visible satellite, the navigation accuracy and Geometric Dilution of Precision (GDOP) of BeiDou-3 (3 GEO-3IGSO-24MEO) are simulated using STK software in Cote d’Ivoire. Using data of five stations in Cote d’Ivoire, the simulation results are compared for BeiDou-3 and GPS. Thus, the results are allowed to possess a database about the positioning performance of BeiDou-3 not only for Cote d’Ivoire but also benefit for surrounding Regions of the Gulf of Guinea.

Positioning Performance Comparison Between GPS and BDS With Data Recorded at Four MGEX Stations

In December 2018, the BeiDou III (BDS-3) basic system was completed and began to provide global services. along with the BeiDou second-generation satellite navigation system (BDS-2) and Beidou first-generation satellite navigation system (BDS-1), the whole BDS has advantages in the number of satellites, coverage, and positioning performance. This paper focuses on the comprehensive evaluation of BDS by comparing the data quality and positioning performance of BDS and those of Global Positioning System (GPS). The performance evaluation and comparison is based on 7-day observation data collected in April 2020 at three different geographical locations in China. The experimental results show that GPS and BDS have a number of significant differences. The number of visible satellites in BDS is twice that of GPS in China. The SNRs of GPS signals of different frequencies are quite different from each other, while BDS signals of different frequencies have very similar SNR observations. BDS-3 and GPS achieve similar positioning performance in terms of internal positional error, external positional accuracy, coordinate time series and Dilution of Precision (DOP). The mean and STD of the internal positional error of GPS and BDS are less than 3 m, while the external positional accuracy of both systems is better than 5 m. It is also observed that the overall variation in coordinate time series of the three coordinates of BDS is slightly smaller than that of GPS. In addition, the BDS DOP is basically equivalent to the GPS DOP, although occasionally the former is greater than the latter. The results are largely contrary to most of the results associated with performance comparison between BDS and GPS reported in the literature. The main reason would be that the number of visible satellites, observations and DOP of BDS are superior to GPS and single BDS-1, BDS-2 or BDS-3 in China. We believe that the development of BDS is still in progress and BDS is making continuous performance enhancement.

Orbit determination algorithm and performance analysis of high‐orbit spacecraft based on GNSS

The study of using the Global Navigation Satellite System (GNSS) to locate Geostationary Earth Orbit (GEO) satellites is very valuable. In this thesis, a new RF strategy is proposed. The back-lobe signal and the main-lobe signal of GNSS satellites are used to provide positioning services for GEO satellites and the receiver antenna beam-forming method is used to improve receiver sensitivity. Additionally, this thesis proposes a satellite selection algorithm that matches the proposed RF strategy. The simulation found that the receiver needs higher sensitivity to detect the back-lobe signal of the GNSS satellite but that the number of visible satellites had doubled and the geometric distribution of the satellite had also been greatly improved. The simulation based on the measured data proves that using a 16*16 antenna array and beam-forming by maximum signal-to-interference and noise ratio algorithm can make five beams of GNSS receivers in GEO orbit and that the side-lobe suppression ratio is up to − 55 dB, which greatly improves the signal receiving gain. After adopting the above technology, the GPS positioning accuracy of GEO spacecraft can be optimised from the order of kilometres to the metres.

Performance Analysis of GPS/BDS Integrated Precise Positioning System Considering Visibility of Satellites

Abstract Research on precise positioning is being actively carried out to provide accurate position information for land transportation. The most significant problem when performing precise positioning in urban canyon is the degradation of performance due to the lack of visible satellites. Prior to open service of BDS, most of the studies on positioning were focused on using GPS/GLONASS integrated navigation system. Since BDS began open service, studies using GPS/BDS have been actively performed in the Asia-Pacific region as it became possible to acquire enough available BDS satellites. The average number of visible satellites in Korea is 9 for GPS and 14 for BDS. In this paper, we analyze the availability of precise positioning using BDS in urban canyon. To do this, we simulate the urban canyon environment by applying the mask to the azimuth and the elevation. We analyze the positioning accuracy using two simulation scenarios. From the results, it is shown that the accuracy of precise positioning in the case where the satellites in the east-west direction are blocked is lowered than that in the case where the satellites in the south-north direction are blocked for the same elevation mask angle. This result comes from the fact that the PDOP increases when the satellites are blocked in the east-west direction. Also, it can be confirmed that the GPS/BDS integrated positioning is available for the high mask angle while the GPS-only positioning is not possible continuously.

Modeling and Assessment of GPS/Galileo/BDS Precise Point Positioning with Ambiguity Resolution

Multi-frequency and multi-GNSS integration is currently becoming an important trend in the development of satellite navigation and positioning technology. In this paper, GPS/Galileo/BeiDou (BDS) precise point positioning (PPP) with ambiguity resolution (AR) are discussed in detail. The mathematical model of triple-system PPP AR and the principle of fractional cycle bias (FCB) estimation are firstly described. With the data of 160 stations in Multi-GNSS Experiment (MGEX) from day of year (DOY) 321-350, 2018, the FCBs of the three systems are estimated and the experimental results show that the range of most GPS wide-lane (WL) FCB is within 0.1 cycles during one month, while that of Galileo WL FCB is 0.05 cycles. For BDS FCB, the classification estimation method is used to estimate the BDS FCB and divide it into GEO and non-GEO (IGSO and MEO) FCB. The variation range of BDS GEO WL FCB can reach 0.5 cycles, while BDS non-GEO WL FCB does not exceed 0.1 cycles within a month. However, the accuracies of GPS, Galileo, and BDS non-GEO narrow-lane (NL) FCB are basically the same. In addition, the number of visible satellites and Position Dilution of Precision (PDOP) values of different combined systems are analyzed and evaluated in this paper. It shows that the triple-system combination can significantly increase the number of observable satellites, optimize the spatial distribution structure of satellites, and is significantly superior to the dual-system and single-system. Finally, the positioning characteristics of single-, dual-, and triple-systems are analyzed. The results of the single station positioning experiment show that the accuracy and convergence speed of the fixed solutions for each system are better than those of the corresponding float solutions. The average root mean squares (RMSs) of the float and the fixed solution in the east and north direction for GPS/Galileo/BDS combined system are the smallest, being 0.92 cm, 0.52 cm and 0.50 cm, 0.46 cm respectively, while the accuracy of the GPS in the up direction is the highest, which is 1.44 cm and 1.27 cm, respectively. Therefore, the combined system can accelerate the convergence speed and greatly enhance the stability of the positioning results.

BDS/GPS/LEO triple-frequency uncombined precise point positioning and its performance in harsh environments

Precise point positioning (PPP) usually takes a few tens of minutes to achieve centimeter-level positioning accuracy, and reliable ambiguity resolution also requires a relatively long observation time. In addition, the time required will be longer in harsh environments such as urban and canyons. These problems limit the application of PPP. Currently, low earth orbit (LEO) enhanced Global Navigation Satellite System (GNSS) can increase the number of visible satellites and optimize observation structure, which is expected to improve the positioning performance of GNSS-only PPP under complex conditions. In this paper, the performance of LEO/GNSS combined PPP in harsh environments is evaluated initially. First, triple-frequency uncombined PPP model is developed. Then, a LEO constellation consisting of 180 polar-orbiting satellites is designed, and BDS-3 and current GPS constellation are also simulated for subsequent analysis. Besides, the corresponding observation simulation is also carried out. In order to better analyze the performance of LEO enhanced GNSS PPP in harsh environments, six sets of contrast experiments are designed. Both PPP float solution and fixed solution are processed. In term of float solution, it usually takes about 30 min for BDS-only to converge into 5 cm, while the BDS/LEO combination only takes about 10 min in extremely harsh environments. Compared with BDS-only, the accuracy of float solution of BDS/GPS, BDS/LEO, BDS/GPS/LEO combined PPP is improved by 42.44%, 73.77%, and 77.43%, respectively. In term of fixed solution, compared BDS-only, the average time to first fix (TTFF) of BDS/GPS, BDS/LEO, BDS/GPS/LEO combination can be shortened from 20.0 min to 10.3 min, 4.8 min and 4.0 min respectively. The fix rate of epochs increases from 83.8% to 91.6%. 96.1% and 96.7% in harsh environments, respectively. Compared with the float solution, the positioning accuracy of fixed solution in N, E, and U directions increases by 3.6%, 4.6%, and 3.2%, respectively.

High-precision Positioning and Deformation Monitoring Analysis of BD/GPS Based on Improved Kalman Filter Fusion

Abstract The real time kinematic of global positioning system (GPS-RTK) provides precise positioning for bridge deformation monitoring and monitoring bridge health status. In order to solve the problem that the satellite signal is vulnerable to the influence of the positioning environment when monitoring bridges in the valleys and urban buildings[1], and the problem that Kalman fusion algorithm is difficult to detect the divergence caused by interruption or wrong data[2]. This paper proposes an improved Kalman filter fusion position method based on the BD/GPS fusion positioning. This improved algorithm introduces the environmental information. The confidence level is calculated with membership function by defining the confidence region of sensor, so as to the fusion weight coefficient is determined. This paper analyzes the performance of BD/GPS positioning in bridge monitoring through comparing the traditional fusion method with the improved fusion method. Experiments show that the improved algorithm eliminates the problem of error divergence; the average number of visible satellites in BD/GPS fusion positioning is increased by 7 compared with that of GPS single system positioning, the GDOP value is reduced by 21.83%, and the positioning error is reduced by 2.51 cm. The feasibility of all-weather monitoring in the mountains, buildings and other areas is verified, and millimeter accuracy is provided, which greatly improves the performance of bridge deformation monitoring.

Galileo Single Point Positioning Assessment Including FOC Satellites in Eccentric Orbits

On August 2016, the Milena (E14) and Doresa (E18) satellites started to broadcast ephemeris in navigation message for testing purposes. As the Galileo constellation is not yet complete. It is very important to have two more satellites available since the position accuracy increases as the number of visible satellites increases. In this article, we examine how the inclusion of the Milena (E14) and Doresa (E18) satellites impacts the position accuracy. The analysis was carried out on 20 days of 1-Hz observations collected by a receiver placed in YEL2IGS (International GNSS service) station. Two different scenarios are considered: the first excludes the measurements coming from the analyzed satellites, while the second one includes them. The analysis was conducted by using a suitable software tool developed in the MATLAB® environment able to compute satellites position from both the broadcast and precise ephemerides, to assess DOP (Dilution Of Precision) parameters and to compute single-point positioning for all Galileo frequencies. The analyses are conducted by using both broadcast and precise ephemeris. The inclusion of the two satellites improves the system availability, varying it from 94.1–97.94%, the DOP parameters, and the percentages of achieved positioning solutions by about 5% regardless of the frequency used. Nevertheless, in the positioning domain, when the broadcast ephemerides are used, the inclusion of the satellites worsens both the horizontal and vertical accuracy of the solution. The deterioration of the horizontal accuracy goes from 0.17 m with E5a frequency measurements to 0.74 m with E1 measurements. The reduction of vertical accuracy goes from 0.68 m for E5a to 1.2 m for E1 measurements. However, if precise ephemerides are used, both the horizontal and the vertical accuracy remain stable, actually for the E5b frequency, the DRMS (Distance Root Mean Squared) improves by almost 0.5 m. The results achieved show that the real drawback to overcome is related to the quality of broadcast ephemeris as, when precise ephemeris are used, the number of solutions achieved is increased by about 5% with an accuracy similar to that obtained when the satellites are excluded.

Triple-frequency carrier phase precise time and frequency transfer models for BDS-3

The third-generation BeiDou navigation satellite system (BDS-3) began providing global positioning, navigation and timing service on December 27, 2018. We present three triple-frequency carrier phase (CP) precise time and frequency transfer models using the BDS-3 B1I/B3I/B2a signals, named IF-PPP1, IF-PPP2 and UC-PPP models, respectively. The BDS B1I/B3I dual-frequency ionospheric-free (IF) model is also introduced, known as IF-PPP0 model. The corresponding mathematical and stochastic models are developed. Two stations located at time laboratories and connected to a high-precision atomic clock are utilized to assess the performances of the proposed CP precise time and frequency transfer models. In addition, the number of visible satellites, position dilution of precision, time dilution of precision, estimated positioning errors, zenith tropospheric delay and inter-frequency bias for two stations are also analyzed. The results show that BDS CP precise time and frequency transfer can achieve better performances with increasing number of BDS-3 observations. The proposed models all can be applied for precise time and frequency transfer with the BDS-3 triple-frequency signals, with stability and accuracy identical to the BDS IF-PPP0 solution. The stability of 10,000 s for the proposed BDS CP precise time and frequency models is better than 1.5 × 10−14.

Precise Onboard Real-Time Orbit Determination with a Low-Cost Single-Frequency GPS/BDS Receiver

The low-cost single-frequency GNSS receiver is one of the most economical and affordable tools for the onboard real-time navigation of numerous remote sensing small/micro satellites. We concentrate on the algorithm and experiments of onboard real-time orbit determination (RTOD) based on a single-frequency GPS/BDS receiver. Through various experiments of processing the real single-frequency GPS/BDS measurements from the Yaogan-30 (YG30) series and FengYun-3C (FY3C) satellites of China, some critical aspects of the onboard RTOD are investigated, such as the optimal force models setting, the effect of different measurements, and the impact of GPS/BDS fusion. The results demonstrate that a gravity model truncated to 55 × 55 order/degree for YG30 and 45 × 45 for FY3C and compensated with an optimal stochastic modeling of empirical accelerations, which minimize the onboard computational load and only result in a slight loss of orbit accuracy, is sufficient to obtain high-precision real-time orbit results. Under the optimal force models, the real-time orbit accuracy of 0.4–0.7 m for position and 0.4–0.7 mm/s for velocity is achievable with the carrier-phase-based solution, while an inferior real-time orbit accuracy of 0.8–1.6 m for position and 0.9–1.7 mm/s for velocity is achieved with the pseudo-range-based solution. Furthermore, although the GPS/BDS fusion only makes little change to the orbit accuracy, it increases the number of visible GNSS satellites significantly, and thus enhances the geometric distribution of GNSS satellites that help suppress the local orbit errors and improves the reliability and availability of the onboard RTOD, especially in some anomalous arcs where only a few GPS satellites are trackable.

Initial Positioning Assessment of BDS New Satellites and New Signals

With the official announcement of open service since the end of 2018, the BeiDou navigation satellite system (BDS) has started to provide global positioning, navigation and timing (PNT) services. Thus, it is worth assessing the positioning service of new BDS satellites and signals. In this paper, we comprehensively assess the system status and the global positioning performance of BDS regarding single point positioning (SPP) and real-time kinematic (RTK) performance. Results show that the signal in space range error (SISRE) of BDS-3 satellites is superior to that of BDS-2 satellites, showing an overall accuracy of 0.71 m versus 0.97 m, which is competitive with GPS and Galileo. With the contribution of BDS-3, the number of global average visible satellites has increased from 5.1 to 10.7, which provides a mean global position dilution of precision (PDOP) value better than 6 at 99.88% and the mean availability of basic PNT performance is also improved from 35.25% to 98.84%. One week of statistical results from 54 globally distributed international GNSS service (IGS) stations show that the root mean square (RMS) of SPP accuracy is 1.1 m in horizontal and 2.2 m in vertical, which is at the same level of GPS. The new B1c and B2a signals show a smaller observation noise than B1I, and SPP performance of B1c is similar to that of B1I. However, the positioning precision is slightly worse at the B2a frequency, which may be due to the inaccurate BDS ionosphere correction. As for short baseline RTK, baseline accuracy is also improved due to the increased number of new BDS satellites.

Analysis of multi-constellation GNSS PPP solutions under phase scintillations at high latitudes

In the past few years, the rapid evolution of multi-constellation navigation satellite systems boosted the development of many scientific and engineering applications. More than 100 satellites will be available in a few years, when all the four global constellations (GPS, GLONASS, Galileo, and Beidou) will be fully deployed. This high number of visible satellites has improved the performance of precise point positioning (PPP) techniques both in terms of accuracy and of session length, especially easing the modeling of ionospheric biases. However, in the presence of severe environmental and atmospheric conditions, the performance of PPP considerably deteriorates. It is the case of high-latitude scenarios, where the satellites coverage is limited, the satellites geometry is poor and ionospheric scintillation are frequent. This paper analyzes the quality of PPP solutions in terms of accuracy and convergence time, for a GNSS station in Antarctica. Single and multi-constellation results are compared, proving the benefits of the availability of a higher number of satellites as well as the improved robustness to the presence of moderate and strong phase scintillations. The use of PPP multi-constellation at high latitudes is indeed essential to guarantee high accuracy, and to obtain a low convergence time, of the order of tens of minutes.

The Influence of Satellite Configuration and Fault Duration Time on the Performance of Fault Detection in GNSS/INS Integration.

For the integration of global navigation satellite system (GNSS) and inertial navigation system (INS), real-time and accurate fault detection is essential to enhance the reliability and precision of the system. Among the existing methods, the residual chi-square detection is still widely used due to its good real-time performance and sensibility of fault detection. However, further investigation on the performance of fault detection for different observational conditions and fault models is still required. In this paper, the principle of chi-square detection based on the predicted residual and least-squares residual is analyzed and the equivalence between them is deduced. Then, choosing the chi-square detection based on the predicted residual as the research object, the influence of satellite configuration and fault duration time on the performance of fault detection is analyzed in theory. The influence of satellite configuration is analyzed from the number and geometry of visible satellites. Several numerical simulations are conducted to verify the theoretical analysis. The results show that, for a single-epoch fault, the location of faulty measurement and the geometry have little effect on the performance of fault detection, while the number of visible satellites has greater influence on the fault detection performance than the geometry. For a continuous fault, the fault detection performance will decrease with the increase of fault duration time when the value of the fault is near the minimal detectable bias (MDB), and faults occurring on different satellite’s measurement will result in different detection results.

Using Regularized Softmax Regression in the GNSS/INS Integrated Navigation System with Nonholonomic Constraints

The integration of global navigation satellite system (GNSS) and Inertial navigation system (INS) is widely implemented in land-vehicle navigation applications. However, the satellite signal is vulnerable in some special urban scenarios, consequently errors in terms of position, velocity and attitude grow rapidly in stand-alone mode especially for low-cost MEMS-based INS. In the conventional tight combination navigation schemes, system works on predicting model during the GNSS signal outage and the positioning accuracy is determined by the precision of the inertial navigation. Besides the lack of observation makes the estimate of inertial navigation error with GNSS information less reliable due to the satellite signal loss. In this paper, an improved non-holonomic constraints (NHC) method based on regularized softmax regression is proposed to enhance navigation precision when the number of visible satellite is insufficient. The velocity constraint condition is applied to simplify the system calculating equations of MEMS-based INS. Furthermore, a regularization softmax regression model based on the collected data is trained to recognize the vehicle motion pattern so as to realize deeper constraints. Simulation and field-test results indicate that the method is beneficial to raise the precision of low-cost GNSS/INS integrated navigation receiver by efficiently reduce the navigation errors.

Performance of Galileo: Global coverage, precise orbit determination, and precise positioning

As one of the major global navigation satellite systems (GNSSs), the performance of the Galileo Satellite Navigation System (Galileo) has been of pressing concern. By the end of June 2018, there were 17 operational satellites that provide navigation and positioning services. However, there is little research evaluating the performance of the Galileo single-system in terms of the average satellite coverage and precise positioning. To address this, this study firstly uses the number of visible satellites to analyze the global average satellite coverage of Galileo. Then different data processing strategies are used to evaluate the accuracy of the Galileo satellite orbit and clock. Finally, the performances of precise point positioning (PPP) and baseline solutions obtained using the Galileo single-system are analyzed. Results show that the number of visible Galileo satellites globally is between 6 and 7 and the time percentage where the number of visible Galileo satellites is greater than or equal to 4 is more than 90% globally. For the orbit determination of Galileo satellites, the Galileo/GPS combined solution is better than that of the Galileo single-system. Using the GeoForschungsZentrum Potsdam (GFZ) multi-GNSS orbit product (indicated by GBM) as a reference, the root mean squares (RMSs) of three-dimension and radial component of Galileo/GPS three-day combined solution are 4.4 cm and 1.8 cm, respectively. The accuracy of the Galileo/GPS single-day combined solution is almost the same as that of the Galileo/GPS three-day combined solution. For the Galileo satellite clock, the Galileo/GPS combined solution provides a better result than the Galileo single-system solution. The convergence times of the static and kinematic PPP solutions of the Galileo single-system are both about 2 h. The average the RMSs of the east (E), north (N), and up (U) components of the static Galileo-only PPP solution are 1.9 cm, 0.5 cm, and 2.0 cm, respectively. Those of the kinematic Galileo-only PPP solution are 2.1 cm, 1.4 cm, and 2.6 cm, respectively. Moreover, the baseline solution accuracy of the ultra-short baseline (48 m) of the Galileo single-system is comparable to GPS. For both static and kinematic solutions, the standard deviations (STDs) of the horizontal and vertical components are better than 6 mm and 8 mm, respectively. The accuracy of baseline solution results of the short baseline (1850 m) is poorer. For both static and kinematic solutions, the STDs of the horizontal and vertical components are better than 1.3 cm and 1.9 cm, respectively.

Efficient signal separation method based on antenna arrays for GNSS meaconing

As an effective deceptive interference technique for military navigation signals, meaconing can be divided into two main types: those that replay directly and those that replay after signal separation. The latter can add different delays to each satellite signal and mislead the victim receiver with respect to any designated position, thus has better controllability and concealment capability. A previous study showed there to be two main spatial processing techniques for separating military signals, whereby either multiple large-caliber antennas or antenna arrays are used to form multiple beams that align with all visible satellites. To ensure sufficient spatial resolution, the main lobe width of the antenna or beam must be sufficiently narrow, which requires the use of a large antenna aperture or a large number of array elements. In this paper, we propose a convenient and effective signal separation method, which is based on an antenna array with fewer elements. While the beam of the array is pointing to a specified satellite, the other satellite signals are regarded as interference and their power is suppressed to a level below the receiver's sensitivity. With this method, the number of array elements depends only on the number of visible satellites, thus greatly reducing the hardware cost and required processing capacity.

Performance of BDS-3: satellite visibility and dilution of precision

We describe a method to assess the performance of the third-generation BeiDou navigation satellite system (BDS-3), in terms of satellite visibility and dilution of precision (DOP), on global and regional scales. Different from traditional methods, this method estimates the satellite visibility and DOP without requiring real or simulated ephemerides. Validated by the reference values derived from real ephemerides of GPS and GLONASS, the estimated number of visible satellites achieves an accuracy better than 0.15, and the estimated DOP values are lower than their reference values by less than 10% on average. Applying this method to BDS-3, with a 5° cutoff elevation angle, results show that the geostationary earth orbit (GEO) and inclined geosynchronous orbit (IGSO) satellites of BDS-3 together contribute 3–6 visible satellites in the area of 60°S–60°N and 50°E–170°E. In this area, the number of visible BDS-3 satellites is 11–14, which is more than GPS and Galileo by 1–3, and GLONASS by 3–7. With better satellite visibility, the average BDS-3 horizontal, vertical, and time DOPs over this area are 0.74, 1.08, and 0.67, which are, respectively, 5%, 9%, and 3% lower than those of GPS and Galileo, 14%, 16%, and 21% lower than those of GLONASS, and 16%, 19% and 14% lower than those of the 24-MEO-only BDS-3.

Improved PPP Ambiguity Resolution with the Assistance of Multiple LEO Constellations and Signals

The fusion of low earth orbit (LEO) constellation and Global Navigation Satellite Systems (GNSS) can increase the number of visible satellites and optimize spatial geometry, which is expected to improve the performance of precise point positioning (PPP) ambiguity resolution (AR). In addition, the multi-frequency signals of LEO satellites can bring a variety of observation combinations, which is potential to further improve the efficiency of PPP AR. In this contribution, multi-frequency PPP AR was achieved with the augmentation of different LEO constellations. Three types of LEO constellations were designed with 60, 192, and 288 satellites. Moreover, the corresponding observation data were simulated with the GNSS observations over the ground stations. The LEO constellations were designed to transmit navigation signals on three frequencies: L1, L2, and L5 at 1575.42, 1227.6, and 1176.45 MHz, respectively, which are consistent with the GPS signals. For PPP AR, the uncalibrated phase delay (UPD) products of GNSS and LEO were estimated first. Furthermore, the quality of UPD products was also analyzed. The research findings show that the performance of estimated LEO UPD is comparable to that of GNSS UPD. Based on the UPD products, LEO-augmented multi-GNSS PPP AR can be achieved. Numerous results show that the performance of single-system and multi-GNSS PPP AR can be significantly improved by introducing the LEO constellations. The augmentation performance is more remarkable in the case of increasing LEO satellites. The time to first fix (TTFF) of the GREC fixed solution can be shortened from 7.1 to 4.8, 1.1, and 0.7 min, by introducing observations of 60-, 192-, and 288-LEO constellations, respectively. The positioning accuracy of multi-GNSS fixed solutions is also improved by about 60%, 80%, and 90% with the augmentation of 60-, 192-, and 288-LEO constellations, respectively. Compared to the dual-frequency solutions, the triple-frequency LEO-augmented PPP fixed solution presents a better performance. The TTFF of GREC fixed solutions is shortened to 33 s with the augmentation of 288-LEO constellation under the triple-frequency environment. It is worth indicating that the 288-satellite LEO-only PPP AR was conducted in dual-frequency and triple-frequency modes, respectively. The averaged TTFFs of both modes are 71.8 s and 55.2 s, respectively. It indicates that LEO constellation with 288 satellites is capable of achieving high-precision positioning independently and shows an even better performance than GNSS-only solutions.

The evaluation of IRNSS/NavIC system’s performance in its primary and secondary service areas–data quality, usability and single point positioning

The Navigation with Indian Constellation (NavIC), also known as Indian regional navigation satellite system, is a regional navigation satellite system recently developed by India. Its service area covers from 30°E to 130°E and from 30°S to 50°N. In this contribution, an assessment of NavIC from aspects of data quality, usability and single point positioning (SPP) performance is carried out using real measured data collected from four sites both within NavIC’s primary and secondary service areas. Data quality of NavIC’s signal is assessed measuring its carrier-to-noise-density ratio and each satellite’s orbital period is calculated using its broadcast ephemeris. Visible satellite number and DOPs values of each site in modes of NavIC-only, GPS-only and GPS/NavIC are counted and calculated respectively. SPP solutions in modes of NavIC-only, GPS-only and GPS/NavIC are also carried out for these four sites. The results show that: the signal strength of NavIC’s L5 frequency generally equals that of GPS in site IISC (Fig. 1); mean orbital periods of IGSO and GEO satellites are 86160.70 s and 86152.03 s respectively; in site IISC (within the primary service area), currently NavIC system can provide an independent positioning service with an accuracy of less than 1 m in the east direction and less than 2 m in north and up directions respectively; the usability and SPP performance can be improved significantly in the mode of GPS/NavIC compared with those in either single mode.

GNSS RTK Positioning Augmented with Large LEO Constellation

It is widely known that in real-time kinematic (RTK) solution, the convergence and ambiguity-fixed speeds are critical requirements to achieve centimeter-level positioning, especially in medium-to-long baselines. Recently, the current status of the global navigation satellite systems (GNSS) can be improved by employing low earth orbit (LEO) satellites. In this study, an initial assessment is applied for LEO constellations augmented GNSS RTK positioning, where four designed LEO constellations with different satellite numbers, as well as the nominal GPS constellation, are simulated and adopted for analysis. In terms of aforementioned constellations solutions, the statistical results of a 68.7-km baseline show that when introducing 60, 96, 192, and 288 polar-orbiting LEO constellations, the RTK convergence time can be shortened from 4.94 to 2.73, 1.47, 0.92, and 0.73 min, respectively. In addition, the average time to first fix (TTFF) can be decreased from 7.28 to 3.33, 2.38, 1.22, and 0.87 min, respectively. Meanwhile, further improvements could be satisfied in several elements such as corresponding fixing ratio, number of visible satellites, position dilution of precision (PDOP) and baseline solution precision. Furthermore, the performance of the combined GPS/LEO RTK is evaluated over various-length baselines, based on convergence time and TTFF. The research findings show that the medium-to-long baseline schemes confirm that LEO satellites do helpfully obtain faster convergence and fixing, especially in the case of long baselines, using large LEO constellations, subsequently, the average TTFF for long baselines has a substantial shortened about 90%, in other words from 12 to 2 min approximately by combining with the larger LEO constellation of 192 or 288 satellites. It is interesting to denote that similar improvements can be observed from the convergence time.