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Impact of New GPS Signals on Positioning Accuracy for Urban Bus Operations

Authors:
Mireille Elhajj at Imperial College London
Mireille Elhajj
Washington Yotto Ochieng at Imperial College London
Washington Yotto Ochieng
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Abstract

This paper analyses for the first time the impact of new GPS signals on positioning accuracy for dynamic urban applications, taking bus operations as an example. The performance assessment addresses both code measurement precision and positioning accuracy. The former is based on signal-to-noise ratio and estimation of multipath and noise by a combination of code and carrier phase measurements. The impact on positioning accuracy is derived by comparing the performance achievable with the conventional single frequency GPS only positioning both relative to reference trajectories from the integration of carrier phase measurements with data from a high grade inertial measurement unit. The results show that L5 code measurements have the highest precision, followed by L1 C/A and L2C. In the positioning domain, there is a significant improvement in two-dimensional and three-dimensional accuracy from dual frequency code measurements over the single frequency measurements, of 39% and 48% respectively, enabling more bus operation services to be supported.
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Impact of New GPS Signals on Positioning Accuracy for
Urban Bus Operations
Journal of Navigation
MIREILLE ELHAJJ, WASHINGTON OCHIENG
DOI: 10.1017/S0373463320000272
Published online: 15 June 2020, pp. 1-22
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Summary
This paper analyses for the first time the impact of new GPS signals on positioning accuracy for dynamic urban
applications, taking bus operations as an example. The performance assessment addresses both code measurement
precision and positioning accuracy. The former is based on signal-to-noise ratio and estimation of multipath and
noise by a combination of code and carrier phase measurements. The impact on positioning accuracy is derived by
comparing the performance achievable with the conventional single frequency GPS only positioning both relative to
reference trajectories from the integration of carrier phase measurements with data from a high grade inertial
measurement unit. The results show that L5 code measurements have the highest precision, followed by L1 C/A and
L2C. In the positioning domain, there is a significant improvement in two-dimensional and three-dimensional
accuracy from dual frequency code measurements over the single frequency measurements, of 39% and 48%
respectively, enabling more bus operation services to be supported.
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... Furthermore, as bus positioning in built environments pose particular challenges in terms of attenuation and blockage of signals, the architecture is designed to improve the continuity and availability of positioning. Traditionally, this has been done by combining position solutions from different sensors and then generating a final position solution, referred to as position domain integration (Elhajj, 2017). However, position domain integration is undesirable since for example, a GPS position solution is required before integration. ...
... There are a wide variety of technologies that could in principle be used to support the positioning/navigation module of bus operation systems including space based (GNSS and their augmentations), terrestrial systems (Dead Reckoning -DR, Wireless Local Area Networks-WLAN and Map Matching-MM) and space/based terrestrial augmentations (Elhajj, 2017). Taking into account the strengths and weaknesses of these technologies (e.g. ...
... Note that there is a wide variety of integration algorithms such as basic and weighted averaging, consensus sensing, weighted least squares, kalman filtering (and its variations including its nonlinear version referred to as the extended kalman filter), neural networks, fuzzy logic and particle filtering (Groves, 2013). Although significant research effort has been dedicated to aspects of the architecture in Fig. 3 (Elhajj, 2017), there are many challenges that are still to be overcome. These challenges can be attributed to the RNP. ...
Urban Bus Positioning: Location based services and high level system architecture
Article
Full-text available
  • Mar 2020
Today’s urban transport systems are dominated by private vehicles, which are significant contributors to traffic congestion and pollution. This is expected to increase as the urban population grows, predicted to account for about 68% of the world’s population by 2050. In comparison to private cars, transport systems dominated by buses produce lower traffic congestion and emissions. Therefore, improvements in bus operation activities most of which require information on bus location (i.e. location based services) should facilitate urban transport sustainability. However, to date there is no agreement globally on the location based services, their location requirements and technologies to deliver significant improvement in bus operations. Therefore, this paper creates for the first time, a comprehensive list of bus operation services and specifies the performance requirements. These are considered together with challenging spatio-temporal characteristics of the urban environment to specify a high-level location determination system architecture for urban bus operations. The services, their requirements, standards and positioning system architecture are essential for the formulation of appropriate policies, regulation, service provision, and development and procurement of urban bus positioning systems.
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... However, it is equally important to determine the accuracy of the GPS. As mentioned earlier, positioning errors can occur in cities with dense development, and it is this issue of determining GPS accuracy in urban environments that was investigated by Merry and Bettinger [17] and Elhajj and Ochieng [18]. The relative and precise accuracy of point positioning has been investigated by El Shouny and Miky [19]. ...
Dynamic Position Accuracy of Low-Cost Global Navigation Satellite System Sensors Applied in Road Transport for Precision and Measurement Reliability
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  • Jun 2024
Low-cost Global Navigation Satellite System (GNSS) sensors have been successfully applied in commercial vehicles’ position monitoring, and they continually raise interest among research audiences both in theoretical and practical aspects. While numerous studies have applied simulations and numerical methods to evaluate the accuracy of the sensors, this paper presents an analysis, supported by actual measurements collected under diversified conditions. The measurements were collected under a variety of conditions, including urban and suburban routes of considerable length, and in accordance with the position in lane applied in most European countries, which is considerably related to the sustainability of road transport. The measurements were collected during driving of three different passenger vehicles, and the response of the measurements to correct, partially correct and incorrect vehicle positions was recorded. Differentiated kinematic conditions and actual dynamic performance during driving were analyzed. This research compared the position accuracy of a low-cost GNSS sensor and a dual-antenna GNSS/INS sensor for vehicle dynamics monitoring. Both types of sensors were operated on all the passenger vehicles and with the same measurement conditions. Statistical hypothesis tests have been considered to compare the results, in accordance with the latest guidelines for carrying out such tests. Studies have indicated that a low-cost GNSS sensor also has satisfactory accuracy. However, this paper points out additional considerations and conclusions. Both the positive and negative results are described and commented on in the paper, including research limitations and suggestions for future measurement and future research agendas, both by the authors and as an inspiration for other researchers.
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... The Global Positioning System (GPS) is currently the major positioning system used globally for purposes of determining location. All types of air [1][2][3], land [4][5][6] and marine [7][8][9] navigation and transportation applications. Moreover, this system is also used in many other applications, e.g., diagnostic [10,11] and engineering [12,13] measurements, scientific studies on the Earth and the environment [14,15], as well as is an important element of time signal transmission systems [16,17]. ...
Experimental Studies on the Relationship Between HDOP and Position Error in the GPS System
Article
Full-text available
  • Mar 2022
2D position error in the Global Positioning System (GPS) depends on the Horizontal Dilution of Precision (HDOP) and User Equivalent Range Error (UERE). The non-dimensional HDOP coefficient, determining the influence of satellite distribution on the positioning accuracy, may be calculated exactly for a given moment in time. However, the UERE value is a magnitude variable in time, especially due to errors in radio propagation (ionosphere and troposphere effects) and it cannot be precisely predicted. The variability of the UERE causes the actual measurements (despite an exact theoretical mathematical correlation between HDOP value and position error) to indicate that position errors differ for the same HDOP value. The aim of this article is to determine the relation between GPS position error and HDOP value. It is possible only statistically, based on an analysis of an exceptionally large measurement sample. To this end, measurement results of a 10-day GPS measurement campaign (900’000 fixes) have been used. For HDOP values (in the range of 0.6-1.8), position errors were recorded and analysed to determine the statistical distribution of GPS position errors corresponding to various HDOP values. The experimental study and statistical analyses showed that the most common HDOP values in the GPS system are magnitudes of: 0.7 (p = 0.353) and 0.8 (p = 0.432). Only 2.77% of fixes indicated an HDOP value larger than 1. Moreover, 95% of measurements featured a geometric coefficient of 0.973 - this is why it may be assumed that in optimal conditions (without local terrain obstacles), the GPS system is capable of providing values of HDOP ≤ 1, with a probability greater than 95% (2σ). Obtaining a low HDOP value, which results to a low GPS position error value, calls for providing a high mean number of satellites (12 or more) and low variability in their number.
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... The main goal behind positioning systems is to provide air [1][2][3][4][5], land [6][7][8][9][10] and marine navigation [11][12][13][14][15] applications with such accuracy that the process is carried out safely. Such applications may include the following: a ship entering a port, driving a car along a route, landing an aircraft at an airport, stopping a tram on a platform, etc. ...
Determination of Navigation System Positioning Accuracy Using the Reliability Method Based on Real Measurements
Article
Full-text available
  • Nov 2021
In navigation, the Twice the Distance Root Mean Square (2DRMS) is commonly used as a position accuracy measure. Its determination, based on statistical methods, assumes that the position errors are normally distributed and are often not reflected in actual measurements. As a result of the widespread adoption of this measure, the positioning accuracy of navigation systems is overestimated by 10-15%. In this paper, a new method is presented for determining the navigation system positioning accuracy based on a reliability model where the system's operation and failure statistics are referred to as life and failure times. Based on real measurements, the method proposed in this article will be compared with the classical method (based on the 2DRMS measure). Real (empirical) measurements made by the principal modern navigation positioning systems were used in the analyses: Global Positioning System (GPS) (168'286 fixes), Differential Global Positioning System (DGPS) (900'000 fixes) and European Geostationary Navigation Overlay Service (EGNOS) (900'000 fixes). Research performed on real data, many of which can be considered representative, have shown that the reliability method provides a better (compared to the 2DRMS measure) estimate of navigation system positioning accuracy. Thanks to its application, it is possible to determine the position error distribution of the navigation system more precisely when compared to the classical method, as well as to indicate those applications that can be used by this system, ensuring the safety of the navigation process.
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... Nowadays, the global positioning system (GPS), in a coded solution, is the primary method of position determination in modern air (Lachapelle et al., 1996;Ochieng et al., 2003;Brodin et al., 2005;Krasuski and Savchuk, 2020), land (Ojeda and Borenstein, 2007;MacLean, 2009;Naranjo et al., 2009;Zandbergen and Barbeau, 2011;Sun et al., 2017;Merry and Bettinger, 2019;Elhajj and Ochieng, 2020;Robustelli et al., 2021) and marine (Grant et al., 2009;Han et al., 2016;Ramesh et al., 2016;Bhatti and Humphreys, 2017;Glomsvoll and Bonenberg, 2017) navigation. Its use depends primarily on the positioning accuracy, which has been constantly changing over the last years, hence GPS applications depend on the current positioning accuracy of that system (Rudnicki and Specht, 2016;Specht, 2019). ...
Consistency Analysis of Global Positioning System Position Errors with Typical Statistical Distributions
Article
  • Jun 2021
Research into statistical distributions of 𝜑, 𝜆 and two-dimensional (2D) position errors of the global positioning system (GPS) enables the evaluation of its accuracy. Based on this, the navigation applications in which the positioning system can be used are determined. However, studies of GPS accuracy indicate that the empirical 𝜑 and 𝜆 errors deviate from the typical normal distribution, significantly affecting the statistical distribution of 2D position errors. Therefore, determining the actual statistical distributions of position errors (1D and 2D) is decisive for the precision of calculating the actual accuracy of the GPS system. In this paper, based on two measurement sessions (900,000 and 237,000 fixes), the distributions of GPS position error statistics in both 1D and 2D space are analysed. Statistical distribution measures are determined using statistical tests, the hypothesis on the normal distribution of 𝜑 and 𝜆 errors is verified, and the consistency of GPS position errors with commonly used statistical distributions is assessed together with finding the best fit. Research has shown that 𝜑 and 𝜆 errors for the GPS system are normally distributed. It is proven that 𝜑 and 𝜆 errors are more concentrated around the central value than in a typical normal distribution (positive kurtosis) with a low value of asymmetry. Moreover, 𝜑 errors are clearly more concentrated than 𝜆 errors. This results in larger standard deviation values for 𝜑 errors than 𝜆 errors. The differences in both values were 25–39%. Regarding the 2D position error, it should be noted that the value of twice the distance root mean square (2DRMS) is about 10–14% greater than the value of R95. In addition, studies show that statistical distributions such as beta, gamma, lognormal andWeibull are the best fit for 2D position errors in the GPS system.
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... These will build a pathway for higher quality of services to society and in cities. A good example of the applied research in this issue is the paper by Elhajj and Ochieng (2020) that analyses for the first time the impact of new GPS signals on positioning accuracy for dynamic urban applications, taking bus operations as an example. In the positioning domain, there is a significant improvement in two-dimensional and three-dimensional accuracy from dual frequency code measurements over the single frequency measurements, of 39% and 48% respectively, enabling more bus operation services to be supported. ...
Navigating Through Pandemic: The Use of Positioning Technologies
Article
  • Nov 2020
The covid-19 pandemic and the enforced lockdown have disrupted many aspects of our lives, including our daily commutes and travels. For our community working on navigation, whether over land or sea or through the air, this is a particularly important time, as both our lives and our research topic have been affected. However, the value and importance of positioning, proximity and location have received more attention than usual. The core part of the mitigation plans of almost all countries is based on social distancing, and this certainly requires some sort of location (either distance and proximity or location). There have been a variety of approaches for managing the infection outbreaks, including mobile phone applications that should be able to identify and alert the potentially infected individuals who have been in contact with covid-19 patients.
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... In contrast, tropospheric delays and orbit errors have the same effect on all carrier signals, irrespective of their frequencies. For the dynamic urban scenarios, tests showed that the use of the L1-L2C ionosphere-free linear combination results in positioning accuracy of 9.032 m (95%) with an improvement of 39% over the L1 C/A code based solution without ionospheric error correction (El Hajj, 2017). Second, multi-frequency GNSS signals can also provide more immunity to interference. ...
Investigation of Context Determination for Advanced Navigation using Smartphone Sensors
Conference Paper
  • Feb 2019
Navigation and positioning is inherently dependent on the context, which comprises both the operating environment and the behaviour of the host vehicle or user. The environment determines the type and quality of radio signals available for positioning, while the behaviour can contribute additional information to the navigation solution. Although many navigation and positioning techniques have been developed, no single one is capable of providing reliable and accurate positioning in all contexts. Therefore, it is necessary for a navigation system to be able to operate across different types of contexts. Context adaptive navigation offers a solution to this problem by detecting the operating contexts and adopting different positioning techniques accordingly. This study focuses on context determination with the available sensors on smartphone, through framework design, behavioural and environmental context detection, context association, comprehensive experimental tests, and system demonstration, building the foundation for a context-adaptive navigation system. In this thesis, the overall framework of context determination is first designed. Following the framework, the behavioural contexts, covering different human activities and vehicle motions, are recognised by different machine learning classifiers in hierarchy. Their classification results are further enhanced by feature selection and a connectivity dependent filter. Environmental contexts are detected from GNSS measurements. Indoor and outdoor environments are first distinguished based on the availability and strength of GNSS signals using a hidden Markov model based method. Within the model, the different levels of connections between environments are exploited as well. Then a fuzzy inference system is designed to enable the further classification of outdoor environments into urban and open-sky. As behaviours and environments are not completely independent, this study also considers context association, investigating how behaviours can be associated within environment detection. Tests in a series of multi-context scenarios have shown that the association mechanism can further improve the reliability of context detection. Finally, the proposed context determination system has been demonstrated in daily scenarios.
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... In contrast, tropospheric delays and orbit errors have the same effect on all carrier signals, irrespective of their frequencies. For the dynamic urban scenarios, tests showed that the use of the L1-L2C ionosphere-free linear combination results in positioning accuracy of 9.032 m (95%) with an improvement of 39% over the L1 C/A code based solution without ionospheric error correction (El Hajj, 2017). Second, multi-frequency GNSS signals can also provide more immunity to interference. ...
Investigation of Context Determination for Advanced Navigation using Smartphone Sensors
Thesis
Full-text available
  • Feb 2019
Navigation and positioning is inherently dependent on the context, which comprises both the operating environment and the behaviour of the host vehicle or user. The environment determines the type and quality of radio signals available for positioning, while the behaviour can contribute additional information to the navigation solution. Although many navigation and positioning techniques have been developed, no single one is capable of providing reliable and accurate positioning in all contexts. Therefore, it is necessary for a navigation system to be able to operate across different types of contexts. Context adaptive navigation offers a solution to this problem by detecting the operating contexts and adopting different positioning techniques accordingly. This study focuses on context determination with the available sensors on smartphone, through framework design, behavioural and environmental context detection, context association, comprehensive experimental tests, and system demonstration, building the foundation for a context-adaptive navigation system. In this thesis, the overall framework of context determination is first designed. Following the framework, the behavioural contexts, covering different human activities and vehicle motions, are recognised by different machine learning classifiers in hierarchy. Their classification results are further enhanced by feature selection and a connectivity dependent filter. Environmental contexts are detected from GNSS measurements. Indoor and outdoor environments are first distinguished based on the availability and strength of GNSS signals using a hidden Markov model based method. Within the model, the different levels of connections between environments are exploited as well. Then a fuzzy inference system is designed to enable the further classification of outdoor environments into urban and open-sky. As behaviours and environments are not completely independent, this study also considers context association, investigating how behaviours can be associated within environment detection. Tests in a series of multi-context scenarios have shown that the association mechanism can further improve the reliability of context detection. Finally, the proposed context determination system has been demonstrated in daily scenarios.
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Simulation and Performance Evaluations of the New GPS L5 and L1 Signals
Article
Full-text available
  • Jan 2017
  • WIREL COMMUN MOB COM
The Global Positioning System (GPS) signals are used for navigation and positioning purposes by a diverse set of users. As a part of GPS modernization effort L5 has been recently introduced for better accuracy and availability service. This paper intends to study and simulate the GPS L1/L5 signal in order to fulfill the following two objectives. The first aim is to point out some important features/differences between current L1 (whose characteristics have been fairly known and documented) and new L5 GPS signal for performance evaluation purpose. The second aim is to facilitate receiver development, which will be designed and assembled later for the actual acquisition of GPS data. Simulation has been carried out for evaluation of correlation properties and link budgeting for both L1 and L5 signals. The necessary programming is performed in Matlab.
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A comparative analysis of measurement noise and multipath for four constellations: GPS, BeiDou, GLONASS and Galileo
Article
Full-text available
  • May 2015
  • SURV REV
With the rapid development of BeiDou system (BDS) and steady progress of Galileo system, the current GNSS (Global Navigation Satellite System) constellations consist of GPS, GLONASS, BeiDou and Galileo. The real signals from the four constellations have been available, which allows us to analyse and compare their measurement noises and multipath effects. In this study, a zero-baseline test is conducted using two ‘Trimble NetR9’ receivers to assess and compare the noises and multipath of measurements on multiple frequencies from the four satellite systems. The zero-baseline double difference approach is utilised to analyse the receiver noises. The code multipath combination and triple-frequency carrier phase combination approaches are exploited to analyse a comprehensive effect of the multipath and noises on the code and carrier phase measurements, respectively. Based on the analysis of the zero-baseline dataset, the results indicate that the code measurement noise levels range from 5 to 25 cm while the carrier phase noise levels vary within 0.9–1.5 mm for different frequencies and constellations. The code multipath and noise (CMN) level for GLONASS is the largest with a root mean square (RMS) value of 39 cm on both G1 and G2 frequencies whereas the Galileo code measurements exhibit a smallest level on the E5 frequency with a RMS value of only 10 cm. The RMS of the carrier phase multipath and noises (PMN) ranges from 1.3 to 2.6 mm for BeiDou and Galileo satellites. By contrast, the triple-frequency carrier phase combinations from the GPS Block IIF satellites demonstrate a much larger RMS value of 5.6 mm owing to an effect of inter-frequency clock biases.
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Article
  • Sep 2004
The United States is planning to implement two new civil signals on the GPS satellites in the next few years. The L2 civil (L2C) signal will be implemented beginning with the first Block IIR-M satellite, anticipated to be launched in 2004. The L5 signal will be implemented beginning with the first Block IIF satellite, anticipated to be launched in 2006. Both new civil signals include design features that make them very different from the only existing civil GPS signal—the L1 C/A-code. In a previous paper, signal structure, cross-correlation protection, tracking loop performance, and multipath were evaluated for each signal. This paper presents additional performance evaluations, such as proposed methods of code acquisition, and receiver tracking thresholds considering platform dynamics and receiver oscillator phase noise. The performance trade-offs between carrier loop bandwidth and loop update time, as well as data demodulation performance, are also evaluated.
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A theoretical performance analysis of the modernized GPS signals
Conference Paper
  • Jun 2008
The frequency and signal design of the American global positioning system (GPS) is currently in a modernization period. The baseline configuration of GPS only consists of two signals on two carrier frequencies (C/A and P(Y) code). At present the existing satellites (IIA, IIR) are replaced by new modernized satellites (IIR-M, IIF) which are capable of transmitting additional signals. The modernization of GPS includes the extension of the frequency plan by a third frequency band (L5). We will evaluate the theoretical potential performance of the baseline signals and the new modernized signals of GPS in terms of positioning accuracy. This includes a discussion of the main error sources and the signal characteristics (signal modulation, carrier frequency and receiver bandwidth). Based on the contributions of the individual error sources we will give estimations of the typical performance of GPS for single-frequency and double-frequency receivers.
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