Pseudorange Corrections Research Articles

Improving GNSS positioning performance of Android smart devices by a novel pseudorange correction method

To achieve high-precision global navigation satellite system (GNSS) positioning of smart devices, it is necessary to correct the pseudorange measurements, especially to reduce time-related errors. Traditional pseudorange smoothing methods fail to cope with measurement anomalies and do not consider the time correlation. Therefore, a time-correlated pseudorange correction (TCPC) method is proposed. The Mann-Kendall trend test and breakpoint detection are used to address data anomalies and pseudorange errors are estimated with an adaptive smoothing method. Using the proposed method, the GNSS receivers can improve the pseudorange accuracy and availability for better single-point positioning performance. The positioning errors are reduced by 10%–45% for different GNSS receivers. Moreover, the circular antenna motion mechanism is used to reduce the measurement correlation and enhance observability. Using the TCPC method in the smartphone antenna motion case, the improvement rates of positioning accuracies are 43%–76% and the horizontal positioning accuracy is improved from meter level to decimeter level.

Maritime DGPS System Positioning Accuracy as a Function of the HDOP in the Context of Hydrographic Survey Performance

The Differential Global Positioning System (DGPS) is a marine navigation system operating at frequencies of 283.5–325 kHz, which is now the primary method for locating vessels in coastal shipping, as well as hydrography and mapping systems worldwide. Its positioning accuracy is determined by the following: the pseudorange error to Global Positioning System (GPS) satellites, the age of pseudorange corrections, and the value of the Horizontal Dilution of Precision (HDOP), which, in terms of accuracy, is crucial in positioning using GPS satellites. In 2020, the International Hydrographic Organization (IHO) introduced a new (the highest) order of hydrographic surveys, i.e., the Exclusive Order, which requires a positioning system to provide an accuracy of 1 m (p = 0.95). The aim of this article is to provide an answer to the question as to whether the maritime DGPS system, whose positioning accuracy is constantly increasing with that of the GPS system, fulfils the requirements for the hydrographic surveys of harbours. To this end, an extensive experimental study on the maritime DGPS system, involving a total of nearly 3.5 million fixes, was conducted. Statistical analyses showed that when ensuring the HDOP values range from 0.8 to 1.4, the DGPS system can be used in hydrographic surveys of harbours.

Inherent Limitations of Smartphone GNSS Positioning and Effective Methods to Increase the Accuracy Utilizing Dual-Frequency Measurements

Xiaomi Mi8 with a Broadcom BCM47755 chip, an Android smartphone that supports multi-constellation (GPS, GLONASS, Galileo, BeiDou, and QZSS) and dual-frequency (L1/E1 and L5/E5), was launched in May 2018. Unlike previously released smartphones, it was technically expected to provide robust precise positioning with a fast ambiguity resolution, which led many researchers to be overly optimistic about the applicability of high-accuracy techniques such as real-time kinematic (RTK) systems and precise point positioning (PPP) of smartphones. The global navigation satellite system (GNSS) raw measurement quality of Android smartphones is, however, inherently far lower than that of general GNSS receivers due to their structure, which accordingly makes it difficult for them to be realized. Considering inherent limitations of smartphones such as low-quality antenna, frequent cycle slips, and the duty cycle, a practical strategy including L5 measurements, pseudo-range corrections for L5, and a weighting method is proposed in this paper. The results show that the proposed methods of L5 differential GNSS (DGNSS) and Doppler-based filtering can guarantee a positioning accuracy of 1.75 m horizontally and 4.56 m vertically in an Android device, which is comparable to the performance of commercial low-cost receivers.

Research on accuracy performance evaluation technology of Beidou GBAS reference receiver

The ground based augmentation system (GBAS) uses ground subsystems including reference receivers to provide differentially correction Global Navigation Satellite System (GNSS) data to improve the overall accuracy and integrity of the system. The accuracy of the GBAS ground subsystem is measured in the pseudo-range domain, so it is necessary to perform pseudo-range domain accuracy testing of the GBAS ground equipment. Based on the B-value method, this paper presents the evaluation process of GBAS pseudo-range domain accuracy based on the BDS-3 new frequency points of B1C and B2a. The B-value methodology is based on broadcast pseudo-range correction data, which covers the differential correction data of all reference stations and considers ground system monitoring, and can reflect the impact of the multipath synthesis effect of different receiver combinations on the accuracy of the pseudo-range domain. The real-collected data shows that the built test system can reach a GAD-B3 accuracy level, and the B-value method can effectively evaluate the pseudo-range domain accuracy of BDS-3 GBAS reference receivers.

A Multipath Processing Technology Based on Multiparameter-Combined Observation in GNSS

In the Global Navigation Satellite System (GNSS), the multipath error affected by many aspects is the main error source that affects satellite navigation, and it is difficult to establish a much more accurate model to analyze it. Based on the ground multipath reflection model, it firstly deeply studies the influence of GNSS satellite orbit parameters on multipath fading frequency and establishes a multipath signal model related to satellite orbit parameters. Secondly, the influence of carrier phase cycle slip, receiver clock adjustment, and GNSS satellite orbit on multiparameter- (MP-) combined observations is analyzed in detail based on the measured data. Finally, aiming at the common phenomenon of code-carrier divergence in the Beidou system, the elevation-based pseudorange correction model and a sidereal filtering are built to correct the MP errors; experiments with measured data show that there is a fluctuation range reduction of 35.7% after sidereal filtering when the receiver reaches a steady state.

A bagging tree-based pseudorange correction algorithm for global navigation satellite system positioning in foliage canyons

Global navigation satellite system is indispensable to provide positioning, navigation, and timing information for pedestrians and vehicles in location-based services. However, tree canopies, although considered as valuable city infrastructures in urban areas, adversely degrade the accuracy of global navigation satellite system positioning as they attenuate the satellite signals. This article proposes a bagging tree-based global navigation satellite system pseudorange error prediction algorithm, by considering two variables, including carrier to noise C/ N0 and elevation angle θe to improve the global navigation satellite system positioning accuracy in the foliage area. The positioning accuracy improvement is then obtained by applying the predicted pseudorange error corrections. The experimental results shows that as the stationary character of the geostationary orbit satellites, the improvement of the prediction accuracy of the BeiDou navigation satellite system solution (85.42% in light foliage and 83.99% in heavy foliage) is much higher than that of the global positioning system solution (70.77% in light foliage and 73.61% in heavy foliage). The positioning error values in east, north, and up coordinates are improved by the proposed algorithm, especially a significant decrease in up direction. Moreover, the improvement rate of the three-dimensional root mean square error of positioning accuracy in light foliage area test is 86% for BeiDou navigation satellite system/global positioning system combination solutions, while the corresponding improvement rate is 82% for the heavy foliage area test.

Lora RTT Ranging Characterization and Indoor Positioning System

In recent years, indoor positioning systems (IPS) are increasingly very important for a smart factory, and the Lora positioning system based on round‐trip time (RTT) has been developed. This paper introduces the ranging characterization, RTT measurement, and position estimation method. In particular, a particle filter localization method‐aided Lora pseudorange fitting correction is designed to solve the problem of indoor positioning; the cumulative distribution function (CDF) criteria are used to measure the quality of the estimated location in comparison to the ground truth location; when the positioning error on the x‐axis threshold is 0.2 m and 0.6 m, the CDF with pseudorange correction is 61% and 99%, which are higher than the 32% and 85% without pseudorange correction. When the positioning error on the y‐axis threshold is 0.2 m and 0.6 m, the CDF with pseudorange correction is 71% and 99.9%, which are higher than the 52% and 94.8% without pseudorange correction.

EGNOS Performance Along Finnish Coast

The purpose of this article is to demonstrate the benefits of EGNOS (European Geostationary Navigation Overlay Service / SBAS in Europe) for the community and inform about the activities that are ongoing for the provision of EGNOS L1 maritime service. EC (European Commission) and GSA (European GNSS Agency) are assessing an EGNOS L1 maritime service with the objective to complement the existing maritime radio-navigation systems (e.g. DGNSS). community is interested in using SBAS for ocean waters, coastal waters and harbour entrances/approaches considering operational needs (IMO Res. 1046), especially where there is no back-up infrastructure or in poorly covered environments. EGNOS L1 Service aims at providing pseudo-range corrections and alert information to the GPS L1 signals for maritime navigation, obtaining enhanced accuracy and ranging integrity information over Europe. In order to ensure a safe use of SBAS by all shipborne receivers, an IEC 61108 standard for SBAS receiver equipment should be published. IEC 61108 is a collection of IEC standards for Maritime navigation and radio-communication equipment and systems - Global navigation satellite systems (GNSS). In consequence, EC, GSA, ESA and ESSP are developing guidelines for manufacturers for the implementation of SBAS in shipborne receivers to be compliant with the operational requirements defined in International Organization (IMO) Resolution A.1046. These guidelines, together with a set of test specifications, intend to support the integration of SBAS in the standardisation process for maritime navigation and radio-communication equipment and systems within IEC framework. One GNSS campaign will be performed along the Finnish coast in order to analyse the EGNOS performance in the border of Northeast EGNOS coverage area. Different types of receivers configured to use SBAS will be on board the vessel to analyse the results. The set of receivers to be used would include maritime receivers, high-end receivers and also new receivers aligned with the future SBAS guidelines. On one side, the EGNOS navigation errors will be obtained with respect to a reference PPP post-processed trajectory. On the other side, the EGNOS availability will be obtained, taking especial attention at the border service coverage area. The EGNOS performance results will be compared with respect to the GPS standalone solution, to verify EGNOS provides an enhanced navigation position. The performance obtained with the receivers will be compared with the operational requirements defined in the IMO Resolution A.1046 (27) to assess the feasibility of EGNOS for some maritime applications. Finally, a deep performance analysis will be done in the Northeast border of EGNOS coverage area for ocean waters, coastal waters and harbour entrances/approaches. Based on the results obtained from a receiver, it will be shown a reliable EGNOS navigation solution with better accuracy than GPS standalone solution. The results aim at confirming that EGNOS L1 service is compliant with the operational requirements defined in the IMO Res. A.1046 (27) for ocean waters, coastal waters and harbour entrances/approaches, being beneficial for maritime community.

Clustering Code Biases between BDS-2 and BDS-3 Satellites and Effects on Joint Solution

China’s BeiDou navigation satellite system (BDS) has finished global constellation construction and can achieve joint solution, simultaneously relying on the B1I + B3I signals of the BDS-2 and BDS-3 satellites. For reasons mostly related to chip shape distortions, navigation satellite observations are corrupted by receiver-dependent code biases. Those biases are brought into observation residuals and degrade the pseudorange correction accuracy. Herein, we present a code bias estimation algorithm, using what we found to be an obvious clustering code bias phenomenon between the BDS-2 and BDS-3 satellites, leading to the systematic biases existing in the BDS-2+3 joint solution. Therefore, we propose a BDS-2+3 joint solution with code bias self-calibration, which can accurately strip off clustering code biases between the BDS-2 and BDS-3 satellites, and can greatly improve precise point positioning (PPP) convergence speed and accuracy. The statistics showed that the residual biases and root mean square (RMS) improved by 36% and 15% and the convergence time improved by approximately 35%. In the convergence stage, the positioning accuracy improved by approximately 38% and 21% in the horizontal and vertical directions, respectively. Meanwhile, in the post-convergence stage, the accuracy improved by approximately 10%.

Aircraft positioning using DGNSS technique for GPS and GLONASS data

Purpose The purpose of this paper is to present the problem of implementation of the differential global navigation satellite system (DGNSS) differential technique for aircraft accuracy positioning. The paper particularly focuses on identification and an analysis of the accuracy of aircraft positioning for the DGNSS measuring technique. Design/methodology/approach The investigation uses the DGNSS method of positioning, which is based on using the model of single code differences for global navigation satellite system (GNSS) observations. In the research experiment, the authors used single-frequency code observations in the global positioning system (GPS)/global navigation satellite system (GLONASS) system from the on-board receiver Topcon HiperPro and the reference station REF1 (reference station for the airport military EPDE in Deblin in south-eastern Poland). The geodetic Topcon HiperPro receiver was installed in Cessna 172 plane in the aviation test. The paper presents the new methodology in the DGNSS solution in air navigation. The aircraft position was estimated using a “weighted mean” scheme for differential global positioning system and differential global navigation satellite system solution, respectively. The final resultant position of aircraft was compared with precise real-time kinematic – on the fly solution. Findings In the investigations it was specified that the average accuracy of positioning the aircraft Cessna 172 in the geocentric coordinates XYZ equals approximately: +0.03 ÷ +0.33 m along the x-axis, −0.02 ÷ +0.14 m along the y-axis and approximately +0.02 ÷ −0.15 m along the z-axis. Moreover, the root mean square errors determining the measure of the accuracy of positioning of the Cessna 172 for the DGNSS differential technique in the geocentric coordinates XYZ, are below 1.2 m. Research limitations/implications In research, the data from GNSS onboard receiver and also GNSS reference receiver are needed. In addition, the pseudo-range corrections from the base stations were applied in the observation model of the DGNSS solution. Practical implications The presented research method can be used in a ground based augmentation system (GBAS) augmentation system, whereas the GBAS system is still not applied in Polish aviation. Social implications The paper is destined for people who work in the area of aviation and air transport. Originality/value The study presents the DGNSS differential technique as a precise method for recovery of aircraft position in civil aviation and this method can be also used in the positioning of aircraft based on GPS and GLONASS code observations.

Weighted moving average-based differential UWB indoor localisation system for high external disturbance environment

Time-based ultra-wideband (UWB) indoor localisation system is affected by clock offset, electromagnetic interference, NLOS and other external conditions, the localisation accuracy and stability will be greatly reduced. Differential GPS (DGPS) technology introduces a reference station, which transmits a pseudo range correction value to a GPS receiver for error correction, thereby largely reducing the localisation error to improve GPS localisation accuracy and localisation stability. In this paper a differential UWB localisation algorithm combined with weighted moving average is proposed by drawing on the experiences of differential GPS, focusing on clock offsets and propagation effects. At the same time, the differential UWB indoor localisation system based on TDOA algorithm is tested by Hainan EVK 2.0 experiments. The experiment results show that Differential UWB indoor localisation system can effectively improve the localisation precision and localisation stability, especially in the case of external disturbances, the overall localisation error is reduced by 23%.

A QUANTITATIVE EVALUATION OF DGPS PERFORMANCE IN THE POSITION AND PSEUDORANGE DOMAINS

Abstract: This study compares in quantitative terms two methods of differential corrections to GPS positioning from the code-based pseudoranges. The differential method calculated from the coordinates (Latitude, Longitude and Altitude), called Position-Domain DGPS, has simple implementation and easy transmission by the correction vector. The second method, called Pseudorange-Domain DGPS has a more elaborate algorithm, focused on the pseudorange correction for each visible satellite, which consumes more processing time and increases the complexity in the transmission of the corrections. Notwithstanding a few variations from this DGPS techniques proposed, this work intends to verify in a numeric way the bias and precision offered by these two well-known methods in different devices and situations, to assess in which context each method would be more advantageous when one what to apply a simple DGPS correction; showing how much is the gain by way of bias the more elaborated method is. The results demonstrate that in favorable conditions, the Position-Domain offered an improvement of approximately 50% in positioning, 35% in dispersion, but without any significant bettering in altimetry or in the maximum values; wile the Pseudorange-Domain method showed 70% in positioning, 75% in precision, 60% for maximum values and numbers close to zero on average altimetry.

Improving DGPS Accuracy by Considering the Correlation of Pseudorange Correction and Satellite Elevation Angle

One of the limitations of Differential Global Positioning Systems (DGPS) is that accuracy decreases as the distance between the user and a base station increases. We have developed a new DGPS positioning strategy that is less affected by baseline length and enables better accuracy. We found correlations between satellite elevation angle and Pseudo-Range Correction (PRC) through extensive tests. As a result, better PRC values were obtained by considering differences in satellite elevation angles at a reference site and the user location. We tested the model for a variety of baseline lengths greater than 250 km, and the positioning accuracy improved by 29–66% compared with traditional DGPS based on a single reference station. Positioning accuracies comparable to those of multi-reference DGPS were achieved in some cases.

Modeling DGNSS Pseudo-Range Correction Messages by Utilizing Satellite Repeat Time.

We developed and validated a pseudo-range correction (PRC) modeling system that can prevent degradation of positioning accuracy even in situations where one cannot obtain PRC messages for Differential Global Navigation Satellite System (DGNSS). A PRC modeling scheme was devised based on the repeat time of GNSS satellites and previously-collected PRC data. The difference between the modeled and real PRC values observed at the reference station showed a bias error of about ±1.0 m and a root mean square error (RMSE) less than 1.5 m. When we applied the predicted PRC to Differential Global Positioning System (DGPS) and Differential BeiDou (DBDS) positioning, horizontal RMSE values were at a level of 1.0 m, while vertical RMSE was in the range of 1.8–3.0 m. We found that modelled PRCs can provide positioning results similar to those based on real PRCs and can provide significant improvement over standalone positioning without PRCs.

Sigma overbound for aircraft landing in presence of day-to-day multipath correlation

PurposeThe purpose of this work is to obtain an overbounded broadcast sigma from actual (non-Gaussian) correction error distribution under the stringent navigation integrity requirements for aircraft precision approach and landing.Design/methodology/approachApproach is statistically to overbound satellite pseudorange correction error distribution with the use of numerical solution of Fisher-Z transformation. Inflation factors for overbounding broadcast sigma are extracted from Fisher-Z transformation based on measured correlation and counted independent identically distributed (iid) sample sizes of true empirical data.FindingsNew overbounded broadcast sigma values for eight long-pass satellites were obtained based on measured actual empirical data and ensured integrity risk at 10−8 probability level. Proposed methodology successfully overbounds ground reflection multipath-type systematic and temporal errors sources.Originality/valueThis paper introduced a new method of accounting for ground reflection multipath for local area augmentation system/ground-based augmentation system navigation integrity. The method is also applicable to statistically overbound any other serially correlated temporal variation in measured data if both correlation values and finite iid sample sizes are known.

해양용 DGPS 운영성 개선을 위한 시스템 경고 임계값 제안

국내에서 운용하고 있는 해양 DGPS는 다중 GNSS 수신기를 활용하여 사용자에게 의사거리 보정정보를 제공하고, 지속적으로 보정정보 의무결성을 감시하는 역할을 수행한다. 해양 DGPS 기준국 (RSIM; reference station and integrity monitor)은 서비스 단절 상황을 막기 위하여 상태 감시 요소에 대한 알람 수준을 설정하여 시스템을 정지시키고, 백업시스템으로 전환하거나, 문제 사항에 대해 파악하여 대응할 수 있도록 한다. 해양 DGPS 기준국 운용 시 이중화 시스템 적용되어 시스템 오작동에 의한 서비스 중단 등의 상황에 대비 할 수 있으나, 백업용 시스템까지 문제가 발생하거나, 외부 요인에 의해 발생하는 서비스 중단에 대해서는 대비할 수 없다. 본 논문에서는 운영자가 사전에 문제 발생 가능성에 대해 확인하여 대응할 수 있도록, 기존의 알람과 정상 상태에 추가적으로 경고 기준값을 제시하였으며, 이를 위해 기준국에서 생성한 상태 감시 정보를 마코프 분석 방식을 통하여 분석하였다. A maritime DGPS in Korea offers pseudo-range correction information and monitors integrity of correction data by using multiple GNSS receivers. The maritime DGPS reference station and integrity monitor service sets alarm threshold value about integrity monitoring parameters for preventing service interruption status. However there is no way to avoid system interruption according to malfunction of backup systems and outside factors. Therefore, in this paper, warning threshold values were proposed for maritime DGPS operator can be counteract in advance. And Markov analysis method was carried out for selection of these warning threshold values.

Cooperative Localization with Reliable Confidence Domains Between Vehicles Sharing GNSS Pseudoranges Errors with No Base Station

Cooperation between road vehicles through information exchange is a promising way to enhance their absolute and relative positions. This paper presents an approach for generating, sharing and applying Global Navigation Satellite System (GNSS) pseudorange corrections through a V2X communication network. Conventionally, differential corrections are generated by fixed base stations with known positions and sent to mobile users. Here, the proposed cooperative method has no central server and the estimation of the raw measurements errors is done in a fully distributed way. Using a model of the correlation of the pseudorange errors and through the knowledge of the local motions of the vehicles obtained by Dead Reckoning (DR) or tracking, a non linear observability shows that the estimation problem is solvable. A cooperative and fully distributed estimation method is then presented using Set Inversion and Constraint propagation techniques. Positions, pseudorange estimated errors and DR data are shared in the network of vehicles and confidence is handled by intervals, in a bounded error context. This allows computing highly reliable confidence domains with no direct range measurements, which is crucial for applications involving close proximity navigation. Indeed, the proposed data fusion framework does not require any linearization of the equations and is insensitive to the data incest problem since the same information can be exploited several times in the computation process without making the estimation over-converge. Results using real measurements are presented to illustrate the performance of the proposed cooperative method in comparison with standalone estimation. A classical sequential Bayesian method has also been implemented on the same data set and compared in terms of accuracy and confidence with a ground truth system.

Computation of satellite clock–ephemeris corrections using a priori knowledge for satellite-based augmentation system

The dual-frequency multi-constellation (DFMC) satellite-based augmentation system (SBAS) should be able to provide a vertical protection level in the range of 10---12 m, which is sufficient to support Category I precision approach operations. Because of the limited data rate of the SBAS signal and the need to augment 91 satellites simultaneously, DFMC SBAS does not broadcast equivalent terms for fast pseudorange corrections in legacy L1-only SBAS. An analysis of the wide area augmentation system (WAAS) suggests that the range error after applying long-term satellite error corrections, known as satellite clock---ephemeris (SCE) corrections in DFMC SBAS, is not accurate enough for Category I operations. Thus, it is necessary to improve the accuracy of these SCE corrections. With the construction of DFMC SBAS, there is an opportunity to upgrade the SCE correction algorithm. Based on the fact that the Global Navigation Satellite System SCE parameter-fitting error constitutes the majority of the SCE error, we propose a method of computing the SCE corrections by combining a priori knowledge of the SCE parameter-fitting error with real-time measurements. A comparison of the user range error after applying WAAS SCE corrections and fast corrections indicates that the proposed method extends the period when a satellite is augmented by 22.9 % and reduces the root mean square error by 27 %.

The integrated use of GPS/GLONASS observations in network code differential positioning

We present the methodology and results of GPS/GLONASS integration in network code differential positioning for regional coverage across Poland using single frequency. Previous studies have only concerned the GPS system and relatively short distances to reference stations of up to tens of kilometers. This study is limited to using GPS and GLONASS. However, the methodology presented applies to all satellite navigation systems. The deterministic and stochastic models, as well as the most important issues in GPS/GLONASS integration are discussed. Two weeks of the GNSS observations were processed using software developed by the first author. In addition to interpolation of pseudorange corrections (PRCs) within the polygon of reference stations, the effect of their extrapolation outside that polygon is also briefly presented. It is well known that the positioning accuracy in a network of heterogeneous receivers can be degraded by GLONASS–FDMA frequency-dependent hardware biases. Our research reveals that when using such networks, the effect of these biases on the network differential GNSS (NDGNSS) positioning results as derived from both GPS and GLONASS can be reduced by simple down-weighting of GLONASS observations. We found that the same approach for the homogeneous equipment is not required; however, it can enhance performance of NDGNSS. Yet, the addition of the down-weighted GLONASS pseudoranges still improves the positioning accuracy by 14–25 %. The representative NDGNSS estimation is characterized by 0.17, 0.12 and 0.32 m RMS errors for the north, east and up component, respectively.

Real-Time Differential Global Poisoning System Stability and Accuracy Improvement by Utilizing Support Vector Machine

Due to errors, accuracy of Global Positioning System is not so high. Therefore, the Real Time Differential Global Poisoning System (RTDGPS) which is based on the successive transmission message of RTCM protocol, is using in real-time applications. Stability and accuracy of the system, significantly depends to a fast transmission of correction messages. These messages come from the reference station to the user stations and affected by the errors related to each satellite. Receiving correction factors which are transmitted by the reference station are facing with time-lag problem, which can increase the error of the RTDGPS. To overcome this problem, prediction algorithms are used. In this research, support vector machine (SVM) model is used to predict the pseudo range correction. Unfortunately, the practical use of SVM is limited because the quality of SVM models depends on a proper setting of SVM and SVM kernel parameters. Therefore, to determine the main parameters of the SVM, both particle swarm optimization (PSO) and genetic algorithm (GA), as two optimization techniques, are used. The proposed methodology has been implemented by a 6-s predicts time step. Simulations showed that the accuracy of GA–SVM and PSO–SVM are equal to 0.186 and 0.154, respectively.