Positioning Performance Analysis Research Articles

Performance Analysis of Relative GPS Positioning for Low-Cost Receiver-Equipped Agricultural Rovers.

Global navigation satellite systems (GNSSs) became an integral part of all aspects of our lives, whether for positioning, navigation, or timing services. These systems are central to a range of applications including road, aviation, maritime, and location-based services, agriculture, and surveying. The Global Positioning System (GPS) Standard Position Service (SPS) provides position accuracy up to 10 m. However, some modern-day applications, such as precision agriculture (PA), smart farms, and Agriculture 4.0, have demanded navigation technologies able to provide more accurate positioning at a low cost, especially for vehicle guidance and variable rate technology purposes. The Society of Automotive Engineers (SAE), for instance, through its standard J2945 defines a maximum of 1.5 m of horizontal positioning error at 68% probability (1σ), aiming at terrestrial vehicle-to-vehicle (V2V) applications. GPS position accuracy may be improved by addressing the common-mode errors contained in its observables, and relative GNSS (RGNSS) is a well-known technique for overcoming this issue. This paper builds upon previous research conducted by the authors and investigates the sensitivity of the position estimation accuracy of low-cost receiver-equipped agricultural rovers as a function of two degradation factors that RGNSS is susceptible to: communication failures and baseline distances between GPS receivers. The extended Kalman filter (EKF) approach is used for position estimation, based on which we show that it is possible to achieve 1.5 m horizontal accuracy at 68% probability (1σ) for communication failures up to 3000 s and baseline separation of around 1500 km. Experimental data from the Brazilian Network for Continuous Monitoring of GNSS (RBMC) and a moving agricultural rover equipped with a low-cost GPS receiver are used to validate the analysis.

Positioning performance analysis of real-time BDS-3 PPP-B2b/INS tightly coupled integration in urban environments

Since 2020, the BeiDou-3 global navigation satellite system has provided real-time precision single-point positioning enhancement services (PPP-B2b). The real-time correction provideded by this service can make real-time precision single-point positioning achieve decimeter-level. However, a dense urban environment may cause frequent interruption of GNSS signals, and PPP-B2b alone cannot achieve continuous precision positioning. This study documents a study that attempts to combine PPP-B2b with an inertial navigation system (INS). A real-time tightly coupled integration model of PPP-B2b/INS based on PPP-B2b services was constructed, and a performance analysis of the tightly coupled integration positioning of PPP-B2b/INS in different urban environments was performed. The experiment shows that in an open-sky environment, the decimeter-level positioning accuracy (North: 31.7; East: 21.3; Up: 39.6 cm and North: 34.1; East: 27.6; Up: 41.0 cm) can only be achieved based on PPP-B2b (BDS only and GPS only), PPP-B2b/INS tightly coupled integration positioning accuracy (North: 17.2; East: 10.3; Up: 19.4 cm), and the convergence time is faster; In a dense urban environment, GNSS signals are frequently interrupted, and the positioning accuracy (North: 141.3; East: 95.2; Up: 156.6 cm and North: 147.5; East: 96.4; Up: 159.3 cm) increases significantly only based on PPP-B2b (BDS only and GPS only), and positioning interruption occurs frequently. However, PPP-B2b/INS tightly coupled integration could still achieve continuous decimetre-level positioning (North: 30.0; East: 28.4; Up: 46.3 cm).

LEO navigation augmentation constellation design and precise point positioning performance analysis based on BDS-3

Low Earth orbit (LEO) satellites have high signal strength and faster geometry changes over short periods, offering unique advantages in navigation augmentation. Integrating LEO satellites into the navigation system can help augment the performance of the global satellite navigation system and break the dilemma of the existing navigation system with limited services in challenging environments. Constellation design is the key before establishing a complete LEO navigation augmentation platform. Therefore, in this study, two LEO navigation augmentation constellations, Polar/Walker (S1) and Walker/Walker (S2) with different inclinations, are designed and optimized using the non-dominated sorting genetic algorithm III (NSGA-III). The global average geometric dilution of precision (GDOP) of BDS-3 is reduced from 1.56 to 0.92 and 0.95, and the average visible satellite number is improved from 11.74 to 27.83 and 25.72 with the navigation augmentation of the optimized constellations. To further validate the navigation augmentation effect of two LEO constellations on BDS-3 precision point positioning (PPP), nine stations at different latitudes were selected for LEO augmented BDS-3 PPP simulation experiments. The results show that after adding S1 and S2 constellations to BDS-3, respectively, the convergence times of the nine stations are reduced by 35.5%∼96.5% and 43.7%∼96.2%, and the positioning accuracy is improved by 5.7%∼71.9% and 24.2%∼69.5%, respectively. Overall, each S1 and S2 constellations can significantly improve the global service performance and PPP performance of BDS-3.

Long-term performance analysis of BDS-3 precise point positioning (PPP-B2b) service

Long-term performance analysis of BDS-3 precise point positioning (PPP-B2b) service

GNSS Observation Generation from Smartphone Android Location API: Performance of Existing Apps, Issues and Improvement

Precise position information available from smartphones can play an important role in developing new location-based service (LBS) applications. Starting from 2016, and after the release of Nougat version (Version 7) by Google, developers have had access to the GNSS raw measurements through the new application programming interface (API), namely android.location (API level 24). However, the new API does not provide the typical GNSS observations directly (e.g., pseudorange, carrier-phase and Doppler observations) which have to be generated by the users themselves. Although several Apps have been developed for the GNSS observations generation, various data analyses indicate quality concerns, from biases to observation inconsistency in the generated GNSS observations output from those Apps. The quality concerns would subsequently affect GNSS data processing such as cycle slip detection, code smoothing and ultimately positioning performance. In this study, we first investigate algorithms for GNSS observations generation from the android.location API output. We then evaluate the performances of two widely used Apps (Geo++RINEX logger and GnssLogger Apps), as well as our newly developed one (namely UofC CSV2RINEX tool) which converts the CSV file to a Receiver INdependent Exchange (RINEX) file. Positioning performance analysis is also provided which indicates improved positioning accuracy using our newly developed tool. Future work finding out the potential reasons for the identified misbehavior in the generated GNSS observations is recommended; it will require a joint effort with the App developers.

Design and Performance Analysis of Positioning and Orientating System for Visible Light Communication

Design and Performance Analysis of Positioning and Orientating System for Visible Light Communication

Performance Analysis of Robust Cooperative Positioning Based on GPS/UWB Integration for Connected Autonomous Vehicles

The accurate position is a key requirement for autonomous vehicles. Although Global Navigation Satellite Systems (GNSS) are widely used in many applications, their performance is often disturbed, particularly in urban areas. Therefore, many studies consider multi-sensor integration and cooperative positioning (CP) approaches to provide additional degrees of freedom to address the shortcomings of GNSS. However, few studies adopted real-world datasets and internode ranging outliers within CP is left untouched, leading to unexpected challenges in practical applications. To address this, we propose a Robust Cooperative Positioning (RCP) scheme that augments the GPS with the Ultra-Wideband (UWB) system. A field experiment is conducted to generate a real-world dataset to evaluate the RCP scheme. Moreover, the analysis of the collected dataset enables us to optimise a simple but effective Robust Kalman Filter (RKF) to mitigate the influence of outlier measurements and improve the robustness of the proposed solution. Finally, a simulated dataset is derived from the real-world data to comprehensively study the performance of the proposed RCP method in urban canyon scenarios. Our results demonstrate that the proposed solution can crucially improve positioning performance when the number of visible GPS satellite is limited and is robust against various adverse effects in such environments.

Network-Based Multiple Operating Points Cooperative Dynamic Positioning of Unmanned Surface Vehicles

This article investigates the network-based multiple operating points cooperative dynamic positioning of multiple unmanned surface vehicles. First, a dynamic positioning system model is established for multiple unmanned surface vehicles. Second, a network-based multiple operating points cooperative dynamic positioning control protocol and a resultant system model for multiple unmanned surface vehicles are constructed under fixed topologies. Third, a networked multiple operating points cooperative dynamic positioning control scheme, which can guarantee the multiple operating points cooperative dynamic positioning error exponentially converge to a bounded region, is proposed. The dynamic positioning control scheme design is then extended to the case of switching topologies. Finally, the multiple operating points cooperative dynamic positioning performance analysis verifies the efficiency of the proposed control schemes.

GPS, BDS-3, and Galileo Inter-Frequency Clock Bias Deviation Time-Varying Characteristics and Positioning Performance Analysis

Multi-frequency observations are now available from GNSSs, thereby bringing new opportunities for precise point positioning (PPP). However, they also introduce new challenges, such as inter-frequency clock bias (IFCB) between the new frequencies and the original dual-frequency observations due to triple-frequency observations, which severely impact the PPP. In this paper, we studied the estimation and correction methods of uncombined inter-frequency clock bias of GPS, BDS-3, and Galileo, analyzed the time-varying characteristics and short-term stability of IFCB, and analyzed the influence of IFCB on the positioning of the GPS, BDS-3, and Galileo, based on a triple-frequency un-differential non-combined PPP model. The obtained results show that the amplitude of Block IIF satellites of the GPS can reach up to 10–20 cm, and the IFCB in BDS-3, Galileo, and GPS Block III satellites can be neglected. After correction by IFCB, the 3D positioning accuracy of the GPS triple-frequency PPP was 1.73 cm and 4.75 cm in the static and kinematic modes, respectively, while the convergence time was 21.64 min and 39.61 min. Compared with the triple-frequency GPS PPP without any correction with IFCB, the static and kinematic 3D positioning accuracy in this work was improved by 27.39% and 17.34%, and the corresponding convergence time was improved by 10.55% and 15.22%, respectively. Furthermore, the delayed IFCB was also used for positioning processing, and it was found that a positioning performance comparable to that of the same day can be obtained. The standard deviation of IFCB for a single satellite was found to be no more than 1 cm, when the IFCB value of a neighboring day was subtracted from the IFCB value of same day, which proves the short-term stability of IFCB.

Combating Single-Frequency Jamming through a Multi-Frequency, Multi-Constellation Software Receiver: A Case Study for Maritime Navigation in the Gulf of Finland.

Today, a substantial portion of global trade is carried by sea. Consequently, the reliance on Global Navigation Satellite System (GNSS)-based navigation in the oceans and inland waterways has been rapidly growing. GNSS is vulnerable to various radio frequency interference. The objective of this research is to propose a resilient Multi-Frequency, Multi-Constellation (MFMC) receiver in the context of maritime navigation to identify any GNSS signal jamming incident and switch to a jamming-free signal immediately. With that goal in mind, the authors implemented a jamming event detector that can identify the start, end, and total duration of the detected jamming event on any of the impacted GNSS signal(s). By utilizing a jamming event detector, the proposed resilient MFMC receiver indeed provides a seamless positioning solution in the event of single-frequency jamming on either the lower or upper L-band. In addition, this manuscript also contains positioning performance analysis of GPS-L5-only, Galileo-E5a-only, and Galileo-E5b-only signals and their multi-GNSS combinations in a maritime operational environment in the Gulf of Finland. The positioning performance of lower L-band GNSS signals in a maritime environment has not been thoroughly investigated as per the authors’ knowledge.

Modeling of BDS-2/BDS-3 single-frequency PPP with B1I and B1C signals and positioning performance analysis

On June 23, 2020, the BDS-3 constellation was fully operational and started providing global positioning navigation and timing services. In the future, BDS-2 will continue to provide services and so it is of great importance to study the combination method of BDS-2 and BDS-3 for BDS precise positioning. Compared with BDS-2, BDS-3 is added new signals B1C, B2a and B2b, and the key is how to handle the signal biases between BDS-2 and BDS-3 in BDS-2/BDS-3 combination processing. With consideration of the signal biases between BDS-2 and BDS-3, we present the BDS-2/BDS-3 single-frequency precise point positioning (PPP) model and study the contribution of BDS-2/BDS-3 combination to BDS precise positioning by using one week data of 36 globally distributed stations from multi-GNSS experiment (MGEX) and international GNSS monitoring and assessment system (iGMAS). It is found that the receiver signal biases between BDS-2 and BDS-3 should be carefully considered no matter B1I or B1C signals are used when BDS-2 and BDS-3 are combined. By comparing the positioning performance of BDS-3 single-frequency PPP (SF-PPP) with B1I and B1C observations, it is noted that the positioning performance is related with the receivers of different networks. The positioning performance with B1I is better than that with B1C at iGMAS stations, while it is opposite at MGEX stations. In addition, the contribution of BDS-2/BDS-3 combination is validated. The convergence performance of BDS-2/BDS-3 SF-PPP is better than that of BDS-2 and BDS-3 SF-PPP. Compared with BDS-3 SF-PPP, the vertical convergence performance of BDS-2/BDS-3 SF-PPP improves by about 43.6% at the 68% confidence level. For the positioning accuracy, BDS-3 and BDS-2/BDS-3 SF-PPP are nearly the same, and improves by about 60% compared with BDS-2 SF-PPP.

Performance analysis of real-time and post-mission kinematic precise point positioning in marine environments

This article focuses on the performance analysis of both real-time and post-mission kinematic precise point positioning (PPP) in challenging marine environments. For this purpose, a real dynamic experiment lasting 6 h was carried out on a lake dam in Çorum City of Turkey. While the kinematic test was continuing, the real-time PPP coordinates were obtained for each measurement epoch with a commercial real-time PPP (RT-PPP) service, namely the Trimble CenterPoint RTX. Then the post-mission PPP (PM-PPP) coordinates were calculated by using Multi-GNSS data and the Multi-GNSS Experiment (MGEX) precise products. The kinematic RT-PPP and PM-PPP results showed that the PPP coordinates were consistent with the relative solution at centimetre and decimetre level in horizontal and height components, respectively. This study implies that PPP technique is a powerful tool for highly accurate positioning in both real-time and post-mission modes, even for dynamic applications in harsh environments.

Positioning performance analysis on combined GPS/BDS precise point positioning

Combining the observation data from five Multi-GNSS Experiment (MGEX) stations with the precise orbit and clock products from Global Positioning System (GPS) and BeiDou Navigation Satellite System (BDS), we studied the model of combined GPS/BDS precise point positioning, and then analyzed the convergence speed and short-time (6 h) positioning accuracy. The calculation results show that in static positioning, the average convergence time of GPS is about 50 min, and its horizontal accuracy is better than 2 cm while the vertical accuracy is better than 4 cm. The convergence speed of combined GPS/BDS is about 40 min, and its positioning accuracy is close to that of GPS. In kinematic positioning, the average convergence time of GPS is about 72 min, and its horizontal accuracy is better than 5 cm while the vertical accuracy is better than 12 cm. The average convergence time of GPS/BDS is about 57 min, and its horizontal accuracy is better than 3 cm while the vertical accuracy is better than 9 cm. Combined GPS/BDS has significantly improved the convergence speed, and its positioning accuracy is slightly than that of GPS.

The Unified Form of Code Biases and Positioning Performance Analysis in Global Positioning System (GPS)/BeiDou Navigation Satellite System (BDS) Precise Point Positioning Using Real Triple-Frequency Data

Multi- system and multi-frequency are two key factors that determine the performance of precise point positioning. Both multi-frequency and multi-system lead to new biases, which are not solved systematically. This paper concentrates on mathematical models of biases, influences of these biases, and positioning performance analysis of different observation models. The biases comprise the inter-frequency clock bias in multi-frequency and the inter-system clock bias in multi-system. The former is the residual differential code biases (DCBs) from receiver clock and satellite clock and usually occurs at the third frequency, the latter is the deviation of the receiver clock errors in different systems. Unified mathematical models of the biases are presented by analyzing the general formula of observation equations. The influences of these biases are validated by experiments with corresponding observation models. Subsequently, the experiments, which are based on the data at five globally distributed stations in Multi-Global Navigation Satellite System (GNSS) Experiment (MGEX) on day of year 100, 2018, assess positioning performance of different observation models with combination of frequencies (dual-frequency or triple- frequency) and systems (BeiDou Navigation Satellite System (BDS) or Global Positioning System (GPS)). The results show that the performances of triple-frequency models are almost as the same level as the dual-frequency models. They provide scientific support for the triple-frequency ambiguity-fixed solution which has a better convergence characteristic than dual-frequency ambiguity-fixed solution. Furthermore, the biases are expressed as an unified form that gives an important and valuable reference for future research on multi-frequency and multi-system precise point positioning.

Assessment of Dual Frequency GNSS Observations from a Xiaomi Mi 8 Android Smartphone and Positioning Performance Analysis

On May 2018 the world’s first dual-frequency Global Navigation Satellite System (GNSS) smartphone produced by Xiaomi equipped with a Broadcom BCM47755 chip was launched. It is able to receive L1/E1/ and L5/E5 signals from GPS, Galileo, Beidou, and GLONASS (GLObal NAvigation Satellite System) satellites. The main aim of this work is to achieve the phone’s position by using multi-constellation, dual frequency pseudorange and carrier phase raw data collected from the smartphone. Furthermore, the availability of dual frequency raw data allows to assess the multipath performance of the device. The smartphone’s performance is compared with that of a geodetic receiver. The experiments were conducted in two different scenarios to test the smartphone under different multipath conditions. Smartphone measurements showed a lower C/N0 and higher multipath compared with those of the geodetic receiver. This produced negative effects on single-point positioning as showed by high root mean square error (RMS). The best positioning accuracy for single point was obtained with the E5 measurements with a DRMS (horizontal root mean square error) of 4.57 m. For E1/L1 frequency, the 2DRMS was 5.36 m. However, the Xiaomi Mi 8, thanks to the absence of the duty cycle, provided carrier phase measurements used for a static single frequency relative positioning with an achieved 2DRMS of 1.02 and 1.95 m in low and high multipath sites, respectively.

Performance Analysis of Relative Positioning using GPS and BDS signals

In general, the satellite signal received by GNSS receivers has errors such as satellite clock error, orbit error, ionospheric delay and tropospheric delay. In environments where high positioning accuracy is required, these error factors can be eliminated by using relative positioning using code measurements with carrier phase measurements. If relative positioning is performed using carrier phase measurements, it is possible to have positioning accuracy of cm level. In this paper, we analyse the positioning accuracy of relative positioning using the L1 signal of GPS and BDS. For this study, we collect GPS and BDS signal using two low-cost receivers. We also designed a software-based platform to perform the relative positioning. Finally, we analyse relative positioning accuracy for GPS/BDS integrated system as well as relative positioning accuracy for GPS and BDS.

RTK model and positioning performance analysis using Galileo four-frequency observations

This paper proposes a real-time kinematic (RTK) model that uses one common reference satellite for the Galileo system with four frequency observations. In the proposed model, the double-differenced (DD) pseudorange and carrier phase biases among the different frequencies are estimated as unknown parameters to recover the integer features of the DD ambiguities among the different frequencies for ambiguity resolution and precise positioning. Analysis results show that the E5a, E5b, and E5 frequencies have virtually the same performance in terms of the positioning accuracy, observation residuals, and ratio values of ambiguity resolution. However, the E1 frequency performs worse than the E5a, E5b, and E5 frequencies. The RTK results for the combination of multiple frequencies are much better than those for a single-frequency observation, the coordinates’ standard deviation is improved about 20–30%, and the ambiguity fix time is improved about 10%.

Network-Based T-S Fuzzy Dynamic Positioning Controller Design for Unmanned Marine Vehicles.

This paper is concerned with a Takagi-Sugeno (T-S) fuzzy dynamic positioning controller design for an unmanned marine vehicle (UMV) in network environments. Network-based T-S fuzzy dynamic positioning system (DPS) models for the UMV are first established. Then, stability and stabilization criteria are derived by taking into consideration an asynchronous difference between the normalized membership function of the T-S fuzzy DPS and that of the controller. The proposed stabilization criteria can stabilize states of the UMV. The dynamic positioning performance analysis verifies the effectiveness of the networked modeling and the controller design.

Quality assessment of GNSS observations from an Android N smartphone and positioning performance analysis using time-differenced filtering approach

The development of low-cost GNSS chips inspired the development of advanced positioning, navigation and timing devices. In ‘I/O of 2016’, Google announced that GNSS observations from devices running the Android version 7 operating system would be available to developers. Providing GNSS application developers the opportunity to develop advanced processing algorithms for accurate position estimation using pseudorange, Doppler and carrier phase observations. The quality of GNSS observations from Android smartphones and their accuracy in estimating position is assessed. The observed carrier-to-noise density ratio (C/N0), pseudorange noise, pseudorange rate error and phase rate error of GNSS observations are evaluated. The results demonstrate that the average (C/N0) value is approximately 10 dB-Hz lower than the representative values obtained from a geodetic-quality antenna and receiver. The station single-difference pseudorange residuals on all available signals vary from − 20 to 20 m, and the value of pseudorange rate varies within ± 10 m/s. In addition, the phase rate and Doppler reaches approximately ± 0.2 m/s. Different from the geodetic receivers, the signal noise ratio (SNR) obtained from smartphone varies more significantly, regardless of elevation angle. Therefore, the SNR-dependent weighting method is preferred during data processing. Furthermore, the results of the static data analysis show that the horizontal and vertical RMS position errors are less than 0.8 and 1.4 m, respectively, when Doppler and phase observations are incorporated into the positioning solution.

Orbit and Positioning Accuracy for New Generation Beidou Satellites during the Earth Eclipsing Period

The Beidou System (BDS) started functioning at the end of 2012. The Yaw-Steering (YS) attitude mode for Inclined Geosynchronous Orbit (IGSO) and Medium Earth Orbit (MEO) satellites in BDS ensures that the solar panels face the Sun. The orbit radial accuracies for IGSO/MEO satellites are 0·5 m and the User Equivalent Range Errors (UERE) are 1·5 m in YS mode. BDS-2 satellites adopt Orbit-Normal (ON) mode to meet the power supply and thermal control requirements of the satellite during deep Earth eclipse periods. In ON mode, long-term orbit ephemeris accuracy monitoring in the Operational Control System (OCS) of BDS indicates that the orbit accuracies for IGSO/MEOs are reduced to a few hundreds of metres, seriously affecting the positioning accuracy and navigation service capability of the BDS system. Solar Radiation Pressure (SRP) is difficult to model in ON mode. Continuous Yaw-Steering (CYS) mode is available for new generation Beidou satellites launched since 2015. The orbit accuracies for these new generation Beidou (BDS-3) satellites were estimated based on BDS monitoring station data and SRP models including ECOM 9/5/3. The evaluation method consisted of four steps, namely, orbit internal consistency analysis, UERE calculation, Satellite Laser Ranging (SLR) data fitting Root Mean Square (RMS) determinations and positioning performance analysis; the data gathering period lasted for more than 60 days and included two CYS periods and one ON period. The experiments showed that the orbit accuracy of the radial component in CYS mode for the BDS-3 satellites degrades by 2 to 3 cm and positioning accuracy degrades only by 1 cm over that in YS mode which is just a small reduction in accuracy compared with the decimetre-level BDS orbit accuracy and the metre-level single point positioning accuracy with BDS pseudorange data. This overcomes declining orbit and positioning accuracy issues in ON mode for BDS-2 satellites. Other results also show that the reliability of BDS has been improved.