Publications
83 results found
Feng S, Jokinen A, Ochieng W, et al., 2014, Receiver autonomous integrity monitoring for fixed ambiguity precise point positioning, Pages: 159-169, ISSN: 1876-1100
There are still many challenges in Precise Point Positioning (PPP) including formulation of mathematical models, fast resolution of integer ambiguities, ambiguity validation and integrity monitoring. Research to date has focused on error modelling and ambiguity resolution. The ambiguity validation and integrity monitoring is still to be investigated in detail. Early research on PPP integrity has addressed the transferability of the Carrier phase based Receiver Autonomous Integrity Monitoring (CRAIM) algorithms developed for conventional Real Time Kinematic positioning (cRTK). However, there are significant differences between cRTK and PPP in the characteristics of the corresponding residual errors. For example, the satellite clock errors are removed in cRTK; while there are still satellites clock errors remaining in PPP after the application of correction products. The magnitude of these residual satellite clock errors depends on the quality of the products used. The residual errors in PPP are expected to be bigger than those in cRTK. These errors have significant negative impacts on ambiguity validation and integrity monitoring. This paper addresses these challenges. A Doubly Non-Central F distribution (DNCF) is justified for the use with popular ratio test for ambiguity validation. The residual errors in the PPP are characterised for the two key processes in RAIM, failure detection and derivation of protection levels. The correction products used for tests were from Centre National d'Etudes Spatiales (CNES). The GNSS measurement data used were from the American National Oceanic and Atmospheric Administration (NOAA). This selection is to ensure that data from same stations used to test the method are not part of the data sets for the generation of correction products. A dataset from 2 NOAA stations was used for testing. Test results show that the PPP algorithm with the DNCF based ambiguity validation can reach sub-decimetre accuracy. The protection levels calculate
Feng S, Wang S, Ochieng W, 2014, A core constellation based multiple-GNSS positioning and integrity monitoring algorithm, Pages: 307-314
With the modernization of existing Global Navigation Satellite Systems (GNSS) and the deployment new GNSS, it is expected that the full operation of multiple constellations is on the horizon. This will bring opportunities for user level positioning and integrity monitoring including more satellites, frequencies, message types, and better signal design and geometry. Considerable research has been undertaken on positioning and integrity monitoring using multiple GNSS. The existing methods do not have constrains on the use of any constellation. However, some countries have made their systems mandatory for some applications. This suggests that countries that own a GNSS are beginning to realise that critically national infrastructures using Position Navigation and Timing (PNT) services and a portion of the national economy associated with GNSS should not be over reliant on other countries. This paper addresses the technical issues of the existing methods and proposes a core constellation (as specified by individual countries) based multiple-GNSS positioning and integrity monitoring algorithm. A Receiver Autonomous Integrity Monitoring (RAIM) is embedded in the positioning algorithm with the core constellation. In order to benefit from the other constellations without compromise the performance of the core constellation, a real time validation algorithm for the measurements from the other constellations is developed using the solution from the core constellation. The measurements from other constellations are pre-processed with conventional methods including correcting for satellite clock, ionosphere effect and troposphere delay. The measurement residual errors relative to the position solution from the core constellation are assessed. Upon passing the validation process, the measurements from other constellations sire integrated to benefit from the feature of multiple constellations and generate a better solution when core constellation suffers problems. The tests were c
Moradi R, Schuster W, Feng S, et al., 2014, A new carrier phase multipath mitigation technique for ionosphere-free combinations, ION ITM (2014)
Moradi R, Schuster W, Feng S, et al., 2014, A new carrier phase multipath mitigation technique for ionosphere-free combination, Institute of Navigation International Technical Meeting 2014, ITM 2014, Pages: 562-567
The ionosphere layer of the atmosphere impacts the speed of electromagnetic waves such as those used by Global Navigation Satellite Systems (GNSS). If dual frequency measurements are available, the dependency of ionospheric errors on the frequency can be exploited to remove a significant fraction of these errors using the ionosphere-free (IF) combination. However, although such combination reduces the ionosphere-induced errors significantly, it also magnifies the noise and multipath errors. A new IF multipath mitigation technique is developed in this paper. In this technique, mitigation is achieved by extracting Inter Frequency carrier Multipath (IFM) errors for Global Positioning System (GPS) L1 and L2 and removing them from the IF carrier phase observation. Three test scenarios with different baselines were conducted using real data sets collected in static mode, and post processed in Real-Time Kinematic (RTK) mode. By mitigating the multipath errors in the ionosphere-free combination using the new technique developed in this paper, the horizontal Root Mean Square (RMS) error was reduced by 27% to 45% and the horizontal mean errors were reduced by 25% to 33%.
Jing S, Zhan X, Liu X, et al., 2014, GNSS Vulnerability Assessment Based on Application Suitability, 27th International Technical Meeting of the Satellite-Division of the Institute-of-Navigation (ION GNSS), Publisher: INST NAVIGATION, Pages: 2291-2298, ISSN: 2331-5911
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- Citations: 4
Zhang X, Zhan X, Feng S, et al., 2014, An Open-Source Real-Time L1/L2 Dual Frequency Software Receiver with an Open Source GPS-Disciplined Clock - Design, Implementation and Test, 27th International Technical Meeting of the Satellite-Division of the Institute-of-Navigation (ION GNSS), Publisher: INST NAVIGATION, Pages: 1376-1382, ISSN: 2331-5911
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- Citations: 2
Sun R, Feng S, Ochieng WY, 2014, An Integrated Solution Based Irregular Driving Detection, 27th International Technical Meeting of the Satellite-Division of the Institute-of-Navigation (ION GNSS), Publisher: INST NAVIGATION, Pages: 548-558, ISSN: 2331-5911
Wang H, Tian J-L, Feng S-Z, et al., 2013, The organ specificity in pathological damage of chronic intermittent hypoxia: an experimental study on rat with high-fat diet., Sleep Breath, Vol: 17, Pages: 957-965
PURPOSE: It is known today that sleep apnea hypopnea syndrome and its characteristic chronic intermittent hypoxia can cause damages to multiple organs, including the cardiovascular system, urinary system, and liver. It is still unclear, however, whether the damage caused by sleep apnea hypopnea syndrome and the severity of the damage are organ-specific. METHODS: This research observed the pathological effects of chronic intermittent hypoxia on rat's thoracic aorta, myocardium, liver, and kidney, under the condition of lipid metabolism disturbance, through establishing the rat model of chronic intermittent hypoxia with high-fat diet by imitating the features of human sleep apnea hypopnea syndrome. In this model, 24 male Wistar rats were randomly divided into three groups: a control group fed by regular diet, a high-fat group fed by high-fat diet, and a high-fat plus intermittent hypoxia group fed by high-fat diet and treated with intermittent hypoxia 7 h a day. At the end of the ninth week, the pathological changes of rat's organs, including the thoracic aorta, myocardium, liver, and kidney are observed (under both optical microscopy and transmission electron microscopy). RESULTS: As the result of the experiment shows, while there was no abnormal effect observed on any organs of the control group, slight pathological changes were found in the organs of the high-fat group. For the high-fat plus intermittent hypoxia group, however, remarkably severer damages were found on all the organs. It also showed that the severity of the damage varies by organ in the high-fat plus intermittent hypoxia group, with the thoracic aorta being the worst, followed by the liver and myocardium, and the kidney being the slightest. CONCLUSIONS: Chronic intermittent hypoxia can lead to multiple-organ damage to rat with high-fat diet. Different organs appear to have different sensitivity to chronic intermittent hypoxia.
Moradi R, Schuster W, Feng S, et al., 2013, Reducing GPS wide lane ambiguity resolution time: A novel carrier phase multipath mitigation technique, Pages: 343-350
Modeling and mitigating carrier multipath errors continues to be a significant challenge for high accuracy positioning using Global Navigation Satellite Systems (GNSS), because the level of multipath is dependent on the operational environment and cannot be mitigated by differencing techniques. Despite significant research in the domain, multipath remains a major problem in high accuracy positioning. The effect of carrier multipath is even more significant when observables are formed by linear combination of measurements from two or more frequencies. Yet, such combinations are commonly in use. For example, in order to facilitate ambiguity fixing for GPS L1, the wide lane observable formed from GPS L1 and L2 measurements is often used to constrain the L1 ambiguity space. Multipath error causes a bias in the estimation of the float solution making it difficult to resolve the integer ambiguities. In this paper, a novel method is developed to mitigate carrier multipath errors for linear combinations, focusing on the wide lane observable. This consists in two stages. In the first stage an observable is derived from combined use of measurements in the same and different frequencies (i.e. GPS L1 and L2), and in the second the observable is applied to mitigate wide lane carrier multipath errors. The proposed method reduces the carrier multipath error in wide lane observables to the level of carrier multipath in the L1 observable, which is significantly smaller. Three test scenarios with different baselines were conducted using real data sets collected in static mode, and post processed in Real-Time Kinematic (RTK) mode. After applying the multipath mitigation method, the time duration to ambiguity resolution were reduced by 25, 48 and 129 seconds, compared to 47, 535 and 427 without the proposed method, for different test scenarios. It means about 53% improvement was achieved in scenario 1, 9% in scenario 2 and 30% in scenario 3.
Moradi R, Schuster W, Feng S, et al., 2013, Carrier Multipath observable: a new carrier phase multipath mitigation technique, New Navigator Seminar
Jokinen A, Feng S, Schuster W, et al., 2013, GLONASS Aided GPS Ambiguity Fixed Precise Point Positioning, JOURNAL OF NAVIGATION, Vol: 66, Pages: 399-416, ISSN: 0373-4633
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- Citations: 30
Jokinen A, Feng S, Schuster W, et al., 2013, Fixed ambiguity Precise Point Positioning (PPP) using tropospheric corrections based on Numeric Weather Modeling (NWM), ION 2013 Pacific PNT
Jokinen A, Feng S, Schuster W, et al., 2013, Integrity monitoring of fixed ambiguity Precise Point Positioning (PPP) solutions, Geo-Spatial Information Science, Vol: 16, Pages: 141-148, ISSN: 1009-5020
Traditional positioning methods, such as conventional Real Time Kinematic (cRTK) rely upon local reference networks to enable users to achieve high-accuracy positioning. The need for such relatively dense networks has significant cost implications. Precise Point Positioning (PPP) on the other hand is a positioning method capable of centimeter-level positioning without the need for such local networks, hence providing significant cost benefits especially in remote areas. This paper presents the state-of-the-art PPP method using both GPS and GLONASS measurements to estimate the float position solution before attempting to resolve GPS integer ambiguities. Integrity monitoring is carried out using the Imperial College Carrier-phase Receiver Autonomous Integrity Monitoring method. A new method to detect and exclude GPS base-satellite failures is developed. A base-satellite is a satellite whose measurements are differenced from other satellite's measurements when using between-satellite-differenced measurements to estimate position. The failure detection and exclusion methods are tested using static GNSS data recorded by International GNSS Service stations both in static and dynamic processing modes. The results show that failure detection can be achieved in all cases tested and failure exclusion can be achieved for static cases. In the kinematic processing cases, failure exclusion is more difficult because the higher noise in the measurement residuals increases the difficulty to distinguish between failures associated with the base-satellite and other satellites. © 2013 Wuhan University.
Nur K, Feng S, Ling C, et al., 2013, Integration of GPS with a WiFi high accuracy ranging functionality, Geo-Spatial Information Science, Vol: 16, Pages: 155-168, ISSN: 1009-5020
High accuracy seamless positioning is required to support a vast number of applications in varying operational environments. Over the last few years, the global positioning system (GPS) has become the de facto technology for positioning applications. However, its performance is limited in indoor and dense urban environments due to multipath as well as signal attenuation and blockage. A number of techniques integrating GPS with other positioning technologies have been developed to address the limitations of standalone GPS in these difficult environments. While most of the developed techniques cover the outages of GPS in such environments, they do not provide acceptable performance, in terms of positioning accuracy, especially for some mission-critical (e.g. safety) applications. This paper proposes a tightly coupled (i.e. in the measurement domain) GPS/WiFi integration method which, in addition to addressing GPS outages, improves the overall positioning accuracy to the meter-level, thus satisfying the requirements of a number of location based services and intelligent transport systems applications. The performance of the proposed GPS/WiFi integration method is assessed for a number of scenarios in a simulation environment for an identified dense urban area in London, UK. © 2013 © 2013 Wuhan University.
Feng S, Jokinen A, Milner C, et al., 2013, New methods for dual constellation single receiver positioning and integrity monitoring, Geo-Spatial Information Science, Vol: 16, Pages: 201-209, ISSN: 1009-5020
Navigation system integrity monitoring is crucial for mission (e.g. safety) critical applications. Receiver autonomous integrity monitoring (RAIM) based on consistency checking of redundant measurements is widely used for many applications. However, there are many challenges to the use of RAIM associated with multiple constellations and applications with very stringent requirements. This paper discusses two positioning techniques and corresponding integrity monitoring methods. The first is the use of single frequency pseudorange-based dual constellations. It employs a new cross constellation single difference scheme to benefit from the similarities while addressing the differences between the constellations. The second technique uses dual frequency carrier phase measurements from GLONASS and the global positioning system for precise point positioning. The results show significant improvements both in positioning accuracy and integrity monitoring as a result of the use of two constellations. The dual constellation positioning and integrity monitoring algorithms have the potential to be extended to multiple constellations. © 2013 © 2013 Wuhan University.
Jokinen A, Feng S, Schuster W, et al., 2013, Improving ambiguity validation and integrity monitoring of Precise Point Positioning (PPP), PROCEEDINGS OF THE 26TH INTERNATIONAL TECHNICAL MEETING OF THE SATELLITE DIVISION OF THE INSTITUTE OF NAVIGATION (ION GNSS 2013), Pages: 1224-1233, ISSN: 2331-5911
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- Citations: 1
Feng S, Jokinen A, Ochieng W, et al., 2012, Multi-constellation RAIM in the presence of multiple faults-a bottom up approach, Pages: 2858-2868
Receiver Autonomous Integrity Monitoring (RAIM) was originally proposed to identify potential faults by consistency checking of redundant measurements in one constellation (i.e. GPS). The limited number of visible satellites imposes constraints on the specification of RAIM algorithms, for example, assuming a single fault. As faults induced by local environments could be present in multiple measurements, the limited number of visible satellites from a single constellation makes it impossible to exclude multiple faults where the requirement for availability is the dominant factor. The availability of multiple constellations including GLONASS and in the future Compass and Galileo offer the opportunity to consider the detection and exclusion of multiple faults. The probability of multiple faults originating from the space and control segments is low. However, it is higher in the case of multiple faults that originate from the user segment due to local environment induced error sources including signal shadowing, Non-Line Of Sight (NLOS), multipath and radio interference. A Top-Down Approach (TDA) is currently employed to deal with multiple faults in multiple constellations. All the measurements are used together or grouped by constellation. In the first approach, if any faults are detected, a data snooping method is used for exclusion. In the presence of multiple faults, this method is time consuming and is therefore, not suitable for real time applications. The second approach is effective if one constellation has multiple faults while the other has only single fault. The availability of this approach is subject to RAIM availability in each constellation. This paper analyses multiple failures modes originating from the user segment and their impact on signal quality. A signal quality model is derived and characterized with the data from an IGS (International GNSS Service) station. On the basis of this model, a group separation approach is applied to exclude a group of
Jokinen A, Feng S, Milner C, et al., 2012, Improving fixed-ambiguity Precise Point Positioning (PPP) convergence time and accuracy by using GLONASS, ION GNSS 2012
Bhatti UI, Ochieng WY, Feng S, 2012, Performance of rate detector algorithms for an integrated GPS/INS system in the presence of slowly growing error, GPS SOLUTIONS, Vol: 16, Pages: 293-301, ISSN: 1080-5370
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- Citations: 28
Jokinen A, Feng S, Ochieng W, et al., 2012, Fixed ambiguity Precise Point Positioning (PPP) with FDE RAIM, Position Location and Navigation Symposium (PLANS), 2012 IEEE/ION
Feng S, Ochieng W, Samson J, et al., 2012, Integrity Monitoring for Carrier Phase Ambiguities, JOURNAL OF NAVIGATION, Vol: 65, Pages: 41-58, ISSN: 0373-4633
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- Citations: 26
Juan JM, Hernandez-Pajares M, Sanz J, et al., 2012, Enhanced Precise Point Positioining for GNSS Users, IEEE Transaction on Geoscience and Remote Sensing, Pages: 1-11
Jokinen A, Feng S, Milner C, et al., 2012, Fixed ambiguity Precise Point Positioning (PPP) with FDE RAIM, ION PLANS
Jokinen A, Feng S, Schuster W, et al., 2012, High integrity GPS/GLONASS Precise Point Positioning (PPP) with GPS ambiguity resolution (in preparation)
Schuster W, Bai J, Feng S, et al., 2012, Integrity monitoring algorithms for airport surface movement, GPS Solutions, Vol: 16, Pages: 65-75
Nur K, Feng S, Ling C, et al., 2012, Application of the Improved FOCUSS for Arrival Time Estimation (IFATE) Algorithm to WLAN High Accuracy Positioning Services, 2012 UBIQUITOUS POSITIONING, INDOOR NAVIGATION, AND LOCATION BASED SERVICE (UPINLBS)
Feng S, Milner C, Jokinen A, et al., 2011, A novel positioning and integrity monitoring algorithm for a multiple constellation receiver, Pages: 2681-2688
With an increasing number of navigation satellites, full operation of multiple constellations is on the horizon. This will bring both opportunities and challenges for user level positioning and integrity monitoring. The opportunities will be facilitated by amongst others, more satellites, frequencies, message types, and better signal design and geometry. The challenges are not only to deal with the differences among satellite navigation systems but also to maximize the benefit from the similarity of multiple constellation signals to develop, for example, low cost, high performance receivers for mass market applications. The current methods for positioning using multiple constellations focus on dealing with differences especially those associated with the time reference. This is dealt with either by the use of information broadcast by the systems or treatment as an unknown to be estimated as part of the solution. This paper proposes a novel positioning and integrity monitoring algorithm for multiple constellation receivers. The positioning method is based on single differences of pairs of measurements from two constellations, for example, the difference between the measurements from a GPS satellite and one or more Galileo satellites. The single difference removes the real receiver clock bias and drift error. Therefore, the inter-system time difference appears as common bias, and is estimated as a virtual receiver clock error. In addition, a carefully selected pair can also mitigate correlated un-modeled errors, thus improving the quality of the positioning solution. One approach to forming the single difference (i.e. basic pairs) is to use satellites in different constellations that are in close proximity. The degree of closeness depends on the user location, time, configuration and status of constellations. For example, signals from the paired satellites with similar elevation and azimuth should help mitigate un-modeled and correlated errors. The corresponding integ
Jiang Z, Groves PD, Ochieng WY, et al., 2011, Multi-constellation GNSS multipath mitigation using consistency checking, Pages: 3889-3902
In a typical urban environment, a mixture of multipath-free, multipath-contaminated and non-line-of-sight (NLOS) propagated GNSS signals are received. The errors caused by multipath-contaminated and NLOS reception are the dominant source of reduced consumer-grade positioning accuracy in the urban environment. Many conventional receiver-based and antenna-based techniques have been developed to mitigate either multipath or NLOS reception with mixed success. Nevertheless, the positioning accuracy can be maximised based on the simple principle of selecting only those signals least contaminated by multipath and NLOS propagation to form the navigation solution. The advent of multi-constellation GNSS provides the opportunity to realise this technique that is potentially low-cost and effective for consumer-grade devices. It may also be implemented as an augmentation to other multipath mitigation techniques. The focus of this paper is signal selection by consistency checking, whereby measurements from different satellites are compared with each other to identify the NLOS and most multipath-contaminated signals. The principle of consistency checking is that multipath-contaminated and NLOS measurements produce a less consistent navigation solution than multipath-free measurements. RAIM-based fault detection operates on the same principle. Three consistency-checking schemes based on single-epoch least-squares residuals are assessed: single sweep, recursive checking and a hybrid version of the first two. Two types of weighting schemes are also considered: satellite elevation-based and signal C/N 0-based weighting. The paper also discussed the different observables that may be used by a consistency-checking algorithm for different applications and their effect on detection sensitivity. Test results for the proposed algorithms are presented using data from both static positioning and stand-alone dynamic positioning experiments. The static data was collected using a pair of survey-
Milner C, Feng S, Jokinen A, et al., 2011, A holistic approach to Carrier-Phase Receiver Autonomous Integrity Monitoring (CRAIM), Pages: 2689-2695
Pseudorange-based integrity monitoring such as Receiver Autonomous Integrity Monitoring (P-RAIM) and its variations, has been studied extensively over recent decades. This has primarily been driven by the safety critical nature of aviation and the important link to the integrity of the positioning and navigation solution required. However, for higher accuracy applications, the more precise carrier phase measurements are used. The applications include positioning both in static and dynamic modes, with the latter employing Real Time Kinematic (RTK) positioning techniques. Furthermore, for mission critical applications such as airport surface movement in which safety is critical, user receiver level integrity monitoring akin to P-RAIM for carrier phase data is required. The state-of-the-art in user receiver level integrity monitoring with carrier phase measurements is formed of two distinct steps; ambiguity validation and a traditional RAIM consistency checking step which assumes fixed ambiguities. This paper proposes a holistic Carrier phase RAIM (C-RAIM) technique that integrates the two processes. The key to accurate and reliable carrier-phase positioning is reliable determination of integer phase ambiguities. A number of methods are currently used, the most popular being the Least-squares AMBiguity Decorrelation Adjustment or LAMBDA, as well as the simpler but sub-optimal integer rounding and sequential integer rounding or bootstrapping. This is followed by a process to confirm the quality of the resulting ambiguities, referred to as ambiguity validation. The main approach to ambiguity validation uses statistical tests such as the ratio test, F-test, W-ratio and χ 2-test which are not justified in theory. However, recent studies have looked to characterise the distribution of the test statistic or incorrect ambiguity vector more accurately in order to provide an estimate of confidence in the ambiguity resolution step. These include; the Integer Aperture (IA) me
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