Global Positioning System Performance Research Articles

Indoor Positioning by Double Deep Q-Network in VLC-Based Empty Office Environment

Recently, artificial intelligence (AI) has been applied in various industries. One such application is indoor user positioning using Big Data. The traditional method for positioning is the global positioning system (GPS). However, the performance of GPS is limited indoors due to propagation loss. Hence, radio frequency (RF)-based communication methods such as WiFi and Bluetooth have been proposed as indoor positioning solutions. However, positioning performance inaccuracies arise due to signal interference caused by RF band saturation. Therefore, this study proposes indoor user positioning based on visible light communication (VLC). The proposed method involves the sequential application of fingerprinting and double deep Q-Network. Fingerprinting is utilized to define the action and state of the double deep Q-Network agent. The agent is designed to learn and locate the reference point (RP) closest to the user’s position in a shorter search time. The core idea of the proposed system is to converge a Cell-ID scheme and fingerprinting. Through this, the initial state of the double deep Q-Network agent can be limited. A limited initial state can increase the positioning speed. Simulation results show that the proposed scheme attains a positioning resolution of less than 13 cm and achieves a processing time of less than 0.03 s to obtain the final position in VLC-based office environments.

Low-Earth-Orbit Satellites and Robust Theory-Augmented GPS/Inertial-Navigation-System Tight Integration for Vehicle-Borne Positioning

Positioning by means of the Global Positioning System (GPS) is a traditional and widely used method. However, its performance is affected by the user environment, such as multi-path effects and poor anti-interference abilities. Therefore, an Inertial Navigation System (INS) has been integrated with GPS to overcome the disadvantages of GPS positioning. INSs do not rely on any external system information and has strong autonomy and independence from the external environment. However, the performance of GPS/INS is visibly degraded in low-observability GPS environments (tall buildings, viaducts, underground tunnels, woods, etc.). Fortunately, with the emergence of Low-Earth-Orbit (LEO) satellites in recent years, the constellation configuration can be extended with the advantages of lower orbits, greater speeds, and richer geometric structures. LEO improves the geometric structure between users and satellites and provides many more observations. Meanwhile, a robust theory approach is applied that can restrain or remove the impact of low-accuracy observations. In this study, we applied LEO data and a robust theory approach to enhance the GPS/INS tight integration. To verify the effectiveness of this method, a set of vehicles and simulated LEO data were analyzed. The results show that robust Kalman filtering (RKF) provides a visible enhancement in the positioning accuracy of GPS/INS integration. This effectively restrains the mutation error and has a smoothing effect on the positioning results. In addition, the addition of LEO data significantly improves the positioning accuracy of a sole GPS and GPS/INS integration. The GPS/LEO/INS integration has the highest positioning accuracy, with Root-Mean-Square Errors (RMSEs) of the north, east, and vertical positions of 2.38 m, 1.94 m, and 2.49 m, respectively, which corresponds to an improvement of 30.21%, 47.43%, and 34.13% compared to sole GPS-based positioning and 8.60%, 17.24%, and 12.14% when compared to the GPS/INS mode. Simultaneously, the simulation results show that LEO and INSs can improve the positioning performance of GPS under GPS-blocked conditions.

Performance of kinematic GPS PPP AR under different ionospheric scintillation conditions

To analyze the performance of Global Positioning System (GPS) Precise Point Positioning (PPP) Ambiguity Resolution (AR) under various ionospheric scintillation environments, we selected GPS data of ionospheric scintillation monitoring receivers (ISMR) and geodetic receivers from high-latitude and low-latitude regions during 2021–2023. We conducted GPS Kinematic PPP using Canadian Spatial Reference System (CSRS) PPP and used the maximum and average values of σφ and S4 as indicators to characterize the intensity of phase scintillation and amplitude scintillation for ISMRs, while the maximum and average values of Rate of Total Electron Content Index (ROTI) to characterize the intensity of ionospheric scintillation for geodetic receivers. We also used ambiguity resolved percentage (ARP) and the 3-Dimensional Root Mean Square (3D RMS) of positioning errors as performance metrics for PPP-AR and PPP. As the maximum and average values of ionospheric scintillation indices increase, the PPP-ARP for high-latitude ISMRs decreases to 90.0 %, and the 3D RMS can reach 0.204 m. During ionospheric quiet conditions, positioning accuracy of GPS PPP can reach the cm-mm level. As the geomagnetic latitude decreases, the scintillation effects on PPP-AR and PPP become more pronounced for high-latitude ISMRs. Compared with high-latitudes, ISMRs located at low-latitudes are more severely affected by scintillation, with PPP-ARP at the station HNLW in China and the station UFBA in Brazil dropping to 80.0 % and 60.0 %, respectively. The 3D RMS can reach 0.288 m and 0.341 m. The results of geodetic receives are consistent with those of ISMRs, with 3D RMS of positioning errors up to 0.240 m and 0.256 m for CYNE and MAL2, respectively, while PPP-ARP drops to 60.4 % and 79.6 %. Additionally, we observed a strong positive correlation between ionospheric scintillation duration and the maximum values of σφ, S4 and ROTI.

DeepGPS: Deep Learning Enhanced GPS Positioning in Urban Canyons

Global Positioning System (GPS) has benefited many novel applications, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e.g.</i> , navigation, ride-sharing, and location-based services, in our daily life. Although GPS works well in most places, its performance in urban canyons is well-known poor, due to the signal reflections of non-line-of-sight (NLOS) satellites. Tremendous efforts have been made to mitigate the impacts of NLOS signals, while previous works heavily rely on precise proprietary 3D city models or other third-party resources, which are not easily accessible. In this paper, we present <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DeepGPS</i> , a deep learning enhanced GPS positioning system that can correct GPS estimations by only considering some simple contextual information. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DeepGPS</i> fuses environmental factors, including building heights and road distribution around GPS's initial position, and satellite statuses to describe the positioning context, and exploits an encoder-decoder network model to implicitly learn the complex relationships between positioning contexts and GPS estimations from massive labeled GPS samples. As a result, the well-trained model can accurately predict the correct position for each erroneous GPS estimation given its positioning context. We further improve the model with a novel constraint mask to filter out invalid candidate locations, and enable continuous localization with a simple mobility model. A prototype system is implemented and experimentally evaluated using a large-scale bus trajectory dataset and real-field GPS measurements. Experimental results demonstrate that <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DeepGPS</i> significantly enhances GPS performance in urban canyons, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e.g.</i> , on average effectively correcting 90.1% GPS estimations with accuracy improvement by 64.6%.

Another Golden Anniversary: NAVSTAR, the Global Positioning System

The global positioning system (GPS) has revolutionized modern society as well as military operations. This article reviews its fascinating history and highlights some aspects of that history that are not well known. Although now universally recognized as one of the greatest technological achievements of the 20th century, in its early days, the program was almost continually at risk of being cut. The relatively small budget of the initial development program forced the designers to become very creative to meet the system's objectives. An international crisis led to the guarantee that GPS would be available to the world, but security concerns resulted in GPS performance for the general public being severely constrained for several years of operation. Currently, there are four independent constellations providing service worldwide and billions of receivers have been produced at a tiny fraction of the cost of early units.

Performance of GPS and IMU sensor fusion using unscented Kalman filter for precise i-Boat navigation in infinite wide waters

The Unmanned Surface Vehicle (USV) navigation system needs an accurate, firm, and reliable performance to avoid obstacles, as well as carry out automatic movements during missions. The Global Positioning System (GPS) is often used in these systems to provide absolute position information. However, the GPS measurements are affected by external conditions such as atmospheric bias and multipath effects. This leads to the inability of the stand-alone GPS to provide accurate positioning for the USV systems. One of the solutions to correct the errors of this sensor is by conducting GPS and Inertial Measurement Unit (IMU) fusion. The IMU sensor is complementary to the GPS and not affected by external conditions. However, it accumulates noise as time elapses. Therefore, this study aims to determine the fusion of the GPS and IMU sensors for the i-Boat navigation system, which is a USV developed by Institut Teknologi Sepuluh Nopember (ITS) Surabaya. Using the Unscented Kalman filter (UKF), sensor fusion was carried out based on the state equation defined by the dynamic and kinematic mathematical model of ship motion in 6 degrees of freedom. Then the performance of this model was tested through several simulations using different combinations of attitude measurement data. Two scenarios were conducted in the simulations: attitude measurement inclusion and exclusion (Scenarios I and II, respectively). The results showed that the position estimation in Scenario II was better than in Scenario I, with the Root Mean Square Error (RMSE) value of 0.062 m. Further simulations showed that the presence of attitude measurement data caused a decrease in the fusion accuracy. The UKF simulation with eight measurement parameters (Scenarios A, B and C) and seven measurement parameters (Scenarios D, E and F), as well as analytical attitude movement, indicated that yaw data had the largest noise accumulation compared to roll and pitch.

Virtual global positioning system construction approach for unmanned surface vessel based on Dempster–Shafer theory and broad learning framework

AbstractIntegrated navigation systems made up of a strap-down inertial navigation system (SINS) and global positioning system (GPS) are increasingly being used to improve the position, speed, and attitude information of unmanned surface vessels (USV). However, a GPS outage could occur due to the dependence of GPS performance on the external environment and the number of available satellites. This study uses an innovative combination of Dempster–Shafer (DS) theory and broad learning (BL) method to design a SINS/GPS integrated navigation system. First, the velocity and position information derived from the SINS and their corresponding GPS were fused using DS fusion rules, while the SINS error was modelled using the BL method. A ‘virtual’ GPS was then designed using the proposed DS–BL approach to provide the speed and position information when the GPS signal was interrupted, thereby ensuring the continuous navigation of the USV. The results of both simulation and sea trial demonstrate that the proposed virtual GPS estimation approach is effective, and the navigational accuracy of the proposed method is superior to other methods.

The Performance of Three-Frequency GPS PPP-RTK with Partial Ambiguity Resolution

The correct ambiguity resolution of real-time kinematic precise point positioning (PPP-RTK) plays an essential role in achieving fast, reliable, and high-precision positioning. However, the ambiguity of incorrect fixing will cause poor PPP-RTK positioning performance. Hence, it is essential to optimize the selected strategy of the ambiguity subset to obtain a more reliable ambiguity resolution performance for PPP-RTK. For this reason, a partial ambiguity resolution (PAR) method combining quality control and Schmidt orthogonalization (Gram–Schmidt) is proposed in this study. To investigate the performance of global positioning system (GPS) dual- and three-frequency PPP-RTK comprehensively, the PAR method based on the Gram–Schmidt method was analyzed and compared with the highest elevation angle method, which considered the satellite with the highest elevation angle as the reference satellite. The performance of ambiguity fixing, atmospheric corrections, and positioning were evaluated using five stations in Belgium and its surrounding area. The results showed average epoch fixing rates of 81.01%, 95.92%, 82.05%, and 97.93% in the dual-frequency highest elevation angle (F2-MAX), dual-frequency Gram–Schmidt (F2-ALT), three-frequency highest elevation angle (F3-MAX), and three–frequency Gram–Schmidt (F3-ALT), respectively. In terms of the time to first fix (TTFF), 89.02%, 94.25%, 90.24%, and 95.69% of the single-differenced (SD) narrow lane (NL) ambiguity fell within 3 min in F2-MAX, F2-ALT, F3-MAX, and F3-ALT, respectively. As far as the ionospheric corrections are concerned, the proportion of SD ionospheric residuals within ±0.25 total electron content units (TECU) were 95.08%, 95.93%, 95.68%, and 96.98% for the F2-MAX, F2-ALT, F3-MAX, and F3-ALT, respectively. The centimeter-level accuracy of both the horizontal and vertical positioning errors can be achieved almost instantaneously in F3-ALT. This is attributed to the accurate and reliable SD NL ambiguity fixing based on the Gram–Schmidt approach.

Variational Bayesian Based IMM Robust GPS Navigation Filter

This paper investigates the navigational performance of Global Positioning System (GPS) using the variational Bayesian (VB) based robust filter with interacting multiple model (IMM) adaptation as the navigation processor. The performance of the state estimation for GPS navigation processing using the family of Kalman filter (KF) may be degraded due to the fact that in practical situations the statistics of measurement noise might change. In the proposed algorithm, the adaptivity is achieved by estimating the time-varying noise covariance matrices based on VB learning using the probabilistic approach, where in each update step, both the system state and time-varying measurement noise were recognized as random variables to be estimated. The estimation is iterated recursively at each time to approximate the real joint posterior distribution of state using the VB learning. One of the two major classical adaptive Kalman filter (AKF) approaches that have been proposed for tuning the noise covariance matrices is the multiple model adaptive estimate (MMAE). The IMM algorithm uses two or more filters to process in parallel, where each filter corresponds to a different dynamic or measurement model. The robust Huber's M-estimation-based extended Kalman filter (HEKF) algorithm integrates both merits of the Huber M-estimation methodology and EKF. The robustness is enhanced by modifying the filter update based on Huber's M-estimation method in the filtering framework. The proposed algorithm, referred to as the interactive multi-model based variational Bayesian HEKF (IMM-VBHEKF), provides an effective way for effectively handling the errors with time-varying and outlying property of non-Gaussian interference errors, such as the multipath effect. Illustrative examples are given to demonstrate the navigation performance enhancement in terms of adaptivity and robustness at the expense of acceptable additional execution time.

Precise Relative Orbit Determination for Chinese TH-2 Satellite Formation Using Onboard GPS and BDS2 Observations

TH-2 is China’s first short-range satellite formation system used to realize interferometric synthetic aperture radar (InSAR) technology. In order to achieve the mission goal of InSAR processing, the relative orbit must be determined with high accuracy. In this study, the precise relative orbit determination (PROD) for TH-2 based on global positioning system (GPS), second-generation BeiDou navagation satellite system (BDS2), and GPS + BDS2 observations was performed. First, the performance of onboard GPS and BDS2 measurements were assessed by analyzing the available data, code multipath errors and noise levels of carrier phase observations. The differences between the National University of Defense Technology (NDT) and the Xi’an Research Institute of Surveying and Mapping (CHS) baseline solutions exhibited an RMS of 1.48 mm outside maneuver periods. The GPS-based orbit was used as a reference orbit to evaluate the BDS2-based orbit and the GPS + BDS2-based orbit. It is the first time BDS2 has been applied to the PROD of low Earth orbit (LEO) satellite formation. The results showed that the root mean square (RMS) of difference between the PROD results using GPS and BDS2 measurements in 3D components was 2.89 mm in the Asia-Pacific region. We assigned different weights to geostationary Earth orbit (GEO) satellites to illustrate the impact of GEO satellites on PROD, and the accuracy of PROD was improved to 7.08 mm with the GEO weighting strategy. Finally, relative orbits were derived from the combined GPS and BDS2 data. When BDS2 was added on the basis of GPS, the average number of visible navigation satellites from TH-2A and TH-2B improved from 7.5 to 9.5. The RMS of the difference between the GPS + BDS2-based orbit and the GPS-based orbit was about 1.2 mm in 3D. The overlap comparison results showed that the combined orbit consistencies were below 1 mm in the radial (R), along-track (T), and cross-track (N) directions. Furthermore, when BDS2 co-worked with GPS, the average of the ambiguity dilution of precision (ADOP) reduced from 0.160 cycle to 0.153 cycle, which was about a 4.4% reduction. The experimental results indicate that millimeter-level PROD results for TH-2 satellite formation can be obtained by using onboard GPS and BDS2 observations, and multi-GNSS can further improve the accuracy and reliability of PROD.

New Methodology for Computing the Aircraft’s Position Based on the PPP Method in GPS and GLONASS Systems

In the field of air navigation, there is a constant pursuit for new navigation solutions for precise GNSS (Global Navigation Satellite System) positioning of aircraft. This study aims to present the results of research on the development of a new method for improving the performance of PPP (Precise Point Positioning) positioning in the GPS (Global Positioning System) and GLONASS (Globalnaja Nawigacionnaja Sputnikovaya Sistema) systems for air navigation. The research method is based on a linear combination of individual position solutions from the GPS and GLONASS systems. The paper shows a computational scheme based on the linear combination for geocentric XYZ coordinates of an aircraft. The algorithm of the new research method uses the weighted mean method to determine the resultant aircraft position. The research method was tested on GPS and GLONASS kinematic data from an airborne experiment carried out with a Seneca Piper PA34-200T aircraft at the Mielec airport. A dual-frequency dual-system GPS/GLONASS receiver was placed on-board the plane, which made it possible to record GNSS observations, which were then used to calculate the aircraft’s position in CSRS-PPP software. The calculated XYZ position coordinates from the CSRS-PPP software were then used in the weighted mean model’s developed optimization algorithm. The measurement weights are a function of the number of GPS and GLONASS satellites and the inverse of the mean error square. The obtained coordinates of aircraft from the research model were verified with the RTK-OTF solution. As a result of the research, the presented solution’s accuracy is better by 11–87% for the model with a weighting scheme as a function of the inverse of the mean error square. Moreover, using the XYZ position from the RTKLIB program, the research method’s accuracy increases from 45% to 82% for the model with a weighting scheme as a function of the inverse of the square of mean error. The developed method demonstrates high efficiency for improving the performance of GPS and GLONASS solutions for the PPP measurement technology in air navigation.

On variations of the decadal precipitable water vapor (PWV) over Turkey

Water in all of its forms takes part nearly in all meteorological activities. Therefore, in climate and atmospheric studies, water vapor plays a central role. Precipitable Water Vapor (PWV) is hard to obtain since its distribution in the troposphere is heterogeneous and anisotropic. Radiosonde observations provide data for mapping the PWV for local to regional scale at low spatial and temporal resolution. Global Positioning System (GPS) provides an alternative option for gathering high temporal and spatial resolution PWV data. In this paper, seasonal PWV variations are studied. Data from six Turkish radiosonde stations were used to validate the performance of GPS estimated PWV. The computed root mean square error (RMSE) of PWV differences between GPS and radiosonde stations is about 1.40–1.82 mm. After assessing the performance of GPS estimated PWV, trends and seasonal variations are computed from a decade worth of 90 GPS stations in Turkey (Jan. 2010–Dec. 2019). These trends at GPS stations were validated using the Mann-Kendall trend test. The test suggests that the trends are statistically significant for all the stations. It has been found that the distinct seasonal cycles are in summer with a maximum water vapor and in winter with a minimum water vapor. The higher amplitudes are located in higher latitudes and lower latitudes (9–15 ± 0.1 mm), and at middle latitudes, amplitudes are considerably lower with 5–7 ± 0.1 mm.

SBAS/EGNOS for Maritime

The Global Navigation Satellite System (GNSS) has become the primary means of obtaining Position, Navigation, and Timing (PNT) information at sea. The current capabilities of the Global Positioning System (GPS) constellation, although adequate for ocean navigation, have some shortfalls for coastal navigation: some user communities have a need for enhanced performance and they can benefit from the available “augmentation” techniques, resulting in improved GPS performance. Nowadays, the users can take advantage of Satellite-Based Augmentation Systems (SBASs). The maritime domain has been used SBAS for several years and it is supported by GNSS receivers used in the recreational and professional sectors. The SBAS/European Geostationary Navigation Overlay Service (EGNOS) can be used to complement the differential GNSS (DGNSS) for the provision of enhanced accuracy and integrity information with additional benefits. There are different possible solutions for the transmission of SBAS/EGNOS information to maritime users, considering that the corrections can be available from different transmission means. The different options for the use of SBAS for maritime navigation, the benefits brought to mariners, as well as the associated regulations, standardization and service provision aspects, are presented in this article.

A Novel Asynchronous UWB Positioning System for Autonomous Trucks in an Automated Container Terminal

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;As a critical technology for autonomous vehicles, high precise positioning is essential for automated container terminals to implement intelligent dispatching and to improve container transport efficiency. Because of the unstable performance of global positioning system (GPS) in some circumstances, an ultra wide band (UWB) positioning system is developed for autonomous trucks in an automated container terminal. In this paper, an asynchronous structure is adopted in the system, and a three-dimensional (3D) localization method is proposed. Other than a traditional UWB positioning system with a server, in this asynchronous system, positions are calculated in the vehicle. Therefore, propagation delays from the server to vehicles are eliminated, and the real-time performance can be significantly improved. Traditional 3D localization methods based on time difference of arrival (TDOA) are mostly invalid with anchors in the same plane. However, in order to guarantee anchors and tags in line of sight (LOS), anchors have to be installed in a vertical plane under the tire cranes. Given this problem, an improved method is presented, which overcomes the matrix singularity. Three hyperboloids can be drawn according to three TDOAs. Either two of them intersect to a plane curve, summing up to three planes in all. Two of them intersect in one line. The line and the hyperboloids intersect at two symmetrical points about the anchor-plane. Then positions of tags can be quickly confirmed as positional relations between trucks and the anchor-plane have been determined when anchors installed. Extensive experiments have been conducted to evaluate the performance in comparison to existing TDOA methods. As shown by experimental results, the proposed method performs better than traditional methods in location accuracy and stability.&lt;/div&gt;&lt;/div&gt;

Multicommodity port throughput from truck GPS and lock performance data fusion

Inland waterways ports are key elements of an efficient multimodal freight transportation system. Data on the capacity and throughput of inland waterway ports by commodity support effective long-term freight planning and travel demand modeling. More specifically, such data can be used to estimate multimodal commodity-based freight fluidity performance measures and to support location selection for freight transload facilities. State-of-the-practice means of obtaining commodity flows data, such as shipper/carrier surveys and vessel and vehicle movements, are limited in their ability to provide monthly or seasonal statistics on individual port operations; rather, they provide annualized statistics for river segments which may contain multiple ports. These limitations are addressed herein by developing a multicommodity assignment model to quantify commodity throughput at inland waterways ports. The model fuses waterborne lock performance monitoring system data, which provides the commodity dimension, and anonymous truck Global Positioning System (GPS) data, which allows for spatial disaggregation. A goal-programming approach minimizes the deviation between known and estimated truck flows at each port. The methodology was applied to the Arkansas River, a 308-mile navigable waterway served by 14 locks and 43 freight ports. Overall, 84% of ports showed less than 20% difference between observed and predicted truck flows. The model is applicable to any inland waterways system with aggregated commodity flow data and truck GPS coverage and fills a critical data gap by describing commodity throughput at inland waterway ports using publicly available data.

Improvement of Single-Frequency GPS Positioning Performance Based on EGNOS Corrections in Algeria

The main objective of the European Geostationary Navigation Overlay System (EGNOS) is to improve the positioning accuracy by correcting several error sources affecting the Global Positioning System (GPS) and to provide integrity information to GPS signals for users in real time. This research presents analysis used to investigate improvement in the performance of single-frequency GPS positioning using EGNOS corrections in Algeria. In this study, we performed position measurements with two calculation approaches, the first based on GPS single-point positioning and the second using EGNOS differential corrections. Positioning accuracy was determined by comparison with the known precise coordinates of the sites; and then the improved ionospheric correction using EGNOS was investigated. The results revealed that GPS + EGNOS performance was significantly improved compared with GPS alone, when measurements of horizontal and vertical accuracy were taken into account, and that the EGNOS corrections improved east and north components slightly, and the up component significantly.

Impact of geometry sensitive satellites on the navigation performance of ground-based augmented GPS

This paper discussed the impact of geometry sensitive of satellites on the navigation performance of ground-based augmentation system (GBAS). The nominal number of satellites (space vehicles, or SVs), defined in RTCA/DO-229E, in the global positioning system (GPS) constellation was used in the analysis. In the quantification of GBAS navigation performance (i.e., the protection level or PL computed at aircraft), full constellation and one and two SV outage scenarios were applied through the search process within all combinations of healthy SV geometries (i.e., subsets of SVs in view). It was observed that some SV combinations, subset geometries obtained after depletion of constellation reduced GBAS navigation performances significantly. These geometries were treated as unsafe for an initiation of intended aircraft precision approach and landing. Further, SVs affecting the integrity and the availability of GBAS in this manner were identified as 'geometry sensitive'. The impact of geometry sensitive SVs on the GBAS navigation performance were quantified and ranked per outage cases.

Improvement of Differential GPS Performance Using Range Measurements Between Satellites

In global positioning system (GPS), inter-satellite link information enables communication between satellites, and inter-satellite range (ISR) represents the distance between satellites used for satellite maintenance. We propose a method to improve position accuracy using distance measurements between satellites, such as ISR. However, ISR information has not been made available to users until now. Therefore, we define distance measurements with inter-satellite ephemeris distance (ISED), which uses satellite coordinates calculated by GPS broadcast ephemeris rather than ISR, and propose a method to improve the position accuracy. ISED accuracy is solely determined by GPS broadcast ephemeris accuracy. GPS ephemeris has recently recorded greater accuracy; therefore, ISED can serve as an additional measurement for user navigation solution. When ISED serves as an additional measurement, the observation matrix is extended, resulting in a reduction in dilution of precision (DOP). Therefore, user accuracy is improved by applying ISED owing to the reduction in DOP. Additionally, the analysis results by applying real experimental data show that DOP, with an extended observation matrix, is more effective in the vertical than the horizontal part. Moreover, the differential GPS (DGPS) shows better performance than the standalone GPS when ISED is applied. The analysis results of applying real data to the method using the proposed ISED showed that vertical position errors were conspicuously decreased compared with horizontal position errors, and the performance was excellent for the DGPS. The proposed method is expected to be highly applicable in aircraft takeoff and landing, where the vertical sector is critical.

GPS + BDS Network Real-Time Differential Positioning Using a Position Domain Estimation Method

The network real-time differential positioning technique is a good choice for meter and sub-meter level’s navigation. More attention has been paid to the Global Positioning System (GPS) and GPS + GLONASS (GLObal NAvigation Satellite System) network real-time differential positioning, but less on the GPS + BDS (BeiDou Navigation Satellite System) combination. This paper focuses on the GPS + BDS network real-time differential positioning. Since the noise of pseudorange observation is large, carrier-phase-smoothed pseudorange is usually used in the network real-time differential positioning to improve the positioning accuracy, while it will be interrupted once the satellite signal is lost or a cycle slip occurs. An improved algorithm in the position domain based on position variation information is proposed. The improved method is immune to the smoothing window and only depends on the number of available satellites. The performance of the network real-time differential positioning using the improved method is evaluated. The performance of GPS + BDS combination is compared with GPS-only solution as well. The results show that the positioning accuracy can be increased by around 10%–40% using the improved method compared with the traditional one. The improved method is less affected by the satellite constellation. The positioning accuracy of GPS + BDS solution is better than that of GPS-only solution, and can reach up to 0.217 m, 0.159 m and 0.330 m in the north, east and up components for the static user station, and 0.122 m, 0.133 m and 0.432 m for the dynamic user station. The positioning accuracy variation does not only depend on whether the user is inside or outside the network, but also on the position relation between the user and network.

Performance of GPS units for deployment on semiaquatic animals.

Global Positioning System (GPS) technology is widely used in wildlife research to study animal movement and habitat use. In order to evaluate the quality and reliability of GPS data, the factors influencing the performance of these devices must be known, especially for semiaquatic species, because terrestrial and aquatic habitat might affect GPS performance differently. We evaluated the location error and fix success rate of three GPS receiver models in stationary tests and on a semi-aquatic mammal, the Eurasian beaver (Castor fiber). The location error during stationary tests was on average 15.7 m, and increased with increasing canopy closure, slope, and horizontal dilution of precision, potentially leading to the erroneous classification of GPS positions when studying habitat use in animals. In addition, the position of the GPS antenna (flat versus 90° tilted) affected the location error, suggesting that animal behavior affects GPS performance. The fix success rate was significantly higher during stationary tests compared to when GPS units were deployed on beavers (94% versus 86%). Further, GPS receivers did not obtain any positions underwater and underground, the latter potentially allowing the estimation of activity periods in animals that use lodges or burrows as shelter. We discuss the possibilities for data screening, the use of buffer zones along the shoreline, and combination with other data loggers to avoid the erroneous classification of GPS positions when studying habitat use.