Satellite-based navigation requires precise knowledge of the structure of the transmitted signals. For GPS, accurate knowledge of the shape of the code correlation peaks is required to ensure no biases are introduced into the position solution. It is generally presumed that all GPS-like satellite signals are virtually identical. However, in 1993 a satellite malfunction introduced significant distortion onto one of the satellite C/A codes. That distortion caused range errors to vary with receiver filter characteristics and code tracking loop implementation. As a result, high-integrity systems such as the Wide Area Augmentation System (WAAS) must implement signal deformation monitors to detect and remove signals that become anomalously distorted. In the future, WAAS will rely on modernized signals from both GPS (L5) and Galileo (E1/L1/E2 and E5A/E5B). This should increase performance for users; however they must still protect against potential signal deformations. Although the International Civil Aviation Organization (ICAO) has agreed on a threat scenario for GPS L1 signals, no such agreement exists for modernized signals. In addition, each of these signals will have different chipping rates and their correlation peak structures will be quite different from that of the GPS C/A code. Their code tracking loop implantations are as yet not well- defined, but may differ somewhat from traditional architectures. An additional complication is the unknown receiver filter characteristics that the new receivers will employ. Each of these factors may render a given signal and/or receiver configuration more or less sensitive to signal deformations. This paper analyzes the range error sensitivity of several modernized signals subjected to distortions of the type considered in the ICAO threat model for signal deformations. To isolate the effects of the signal-in-space deformation errors, it assumes an ideal, wideband receiver filter and basic early-minus-late code tracking implementations for the new codes. It also compares the distortion-induced range errors for the new codes to those currently modeled for the C/A code. Finally, these results are used to motivate threat model refinements and receiver tracking loop constraints that minimize the affects of this error source for the modernized GNSS signals.
{"title":"Effects of Signal Deformations on Modernized GNSS Signals","authors":"R. E. Phelts, D. Akos","doi":"10.5081/JGPS.5.1.2","DOIUrl":"https://doi.org/10.5081/JGPS.5.1.2","url":null,"abstract":"Satellite-based navigation requires precise knowledge of the structure of the transmitted signals. For GPS, accurate knowledge of the shape of the code correlation peaks is required to ensure no biases are introduced into the position solution. It is generally presumed that all GPS-like satellite signals are virtually identical. However, in 1993 a satellite malfunction introduced significant distortion onto one of the satellite C/A codes. That distortion caused range errors to vary with receiver filter characteristics and code tracking loop implementation. As a result, high-integrity systems such as the Wide Area Augmentation System (WAAS) must implement signal deformation monitors to detect and remove signals that become anomalously distorted. In the future, WAAS will rely on modernized signals from both GPS (L5) and Galileo (E1/L1/E2 and E5A/E5B). This should increase performance for users; however they must still protect against potential signal deformations. Although the International Civil Aviation Organization (ICAO) has agreed on a threat scenario for GPS L1 signals, no such agreement exists for modernized signals. In addition, each of these signals will have different chipping rates and their correlation peak structures will be quite different from that of the GPS C/A code. Their code tracking loop implantations are as yet not well- defined, but may differ somewhat from traditional architectures. An additional complication is the unknown receiver filter characteristics that the new receivers will employ. Each of these factors may render a given signal and/or receiver configuration more or less sensitive to signal deformations. This paper analyzes the range error sensitivity of several modernized signals subjected to distortions of the type considered in the ICAO threat model for signal deformations. To isolate the effects of the signal-in-space deformation errors, it assumes an ideal, wideband receiver filter and basic early-minus-late code tracking implementations for the new codes. It also compares the distortion-induced range errors for the new codes to those currently modeled for the C/A code. Finally, these results are used to motivate threat model refinements and receiver tracking loop constraints that minimize the affects of this error source for the modernized GNSS signals.","PeriodicalId":237555,"journal":{"name":"Journal of Global Positioning Systems","volume":"81 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114389569","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Offshore platforms undergo subsidence, especially due to production activities. The monitoring of such subsidence requires specialised technique (i.e. GPS) as the platforms are situated at sea (i.e. hundreds of kms from mainland). Unfortunately standard GPS processing procedure is unable to achieve the required accuracy (several cm) over long baselines. The research focuses on the development of processing strategy (i.e. estimation and subsidence analysis) for monitoring of offshore platform subsidence using three permanent GPS stations of the Malaysia Active GPS system (MASS). The estimation of each epoch employs Bernese GPS software, followed by subsidence analysis using in-house software. Preliminary results are also shown.
{"title":"Monitoring of Offshore Platform Subsidence Using Permanent GPS Stations","authors":"H. Setan, R. Othman","doi":"10.5081/JGPS.5.1.17","DOIUrl":"https://doi.org/10.5081/JGPS.5.1.17","url":null,"abstract":"Offshore platforms undergo subsidence, especially due to production activities. The monitoring of such subsidence requires specialised technique (i.e. GPS) as the platforms are situated at sea (i.e. hundreds of kms from mainland). Unfortunately standard GPS processing procedure is unable to achieve the required accuracy (several cm) over long baselines. The research focuses on the development of processing strategy (i.e. estimation and subsidence analysis) for monitoring of offshore platform subsidence using three permanent GPS stations of the Malaysia Active GPS system (MASS). The estimation of each epoch employs Bernese GPS software, followed by subsidence analysis using in-house software. Preliminary results are also shown.","PeriodicalId":237555,"journal":{"name":"Journal of Global Positioning Systems","volume":"33 1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123520799","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A project to build a GPS receiver using an FPGA for base-band processing began in 2004. The new receiver platform uses a commonly available RF front end ASIC to convert the GPS signals to a suitable IF. The digital design for baseband processing is normally a reasonably straight forward task. However, because the received GPS signals are at such low levels this presents some challenges. One of the main considerations is to avoid contamination of the incoming signals with interference that can be generated from the digital electronics when using an FPGA. In this paper we describe the hardware design process with a focus on avoiding interference while still allowing complex FPGA logic to operate alongside sensitive GPS RF signal processing.
{"title":"FPGA based GPS receiver design considerations","authors":"K. Parkinson, A. Dempster, P. Mumford, C. Rizos","doi":"10.5081/JGPS.5.1.70","DOIUrl":"https://doi.org/10.5081/JGPS.5.1.70","url":null,"abstract":"A project to build a GPS receiver using an FPGA for base-band processing began in 2004. The new receiver platform uses a commonly available RF front end ASIC to convert the GPS signals to a suitable IF. The digital design for baseband processing is normally a reasonably straight forward task. However, because the received GPS signals are at such low levels this presents some challenges. One of the main considerations is to avoid contamination of the incoming signals with interference that can be generated from the digital electronics when using an FPGA. In this paper we describe the hardware design process with a focus on avoiding interference while still allowing complex FPGA logic to operate alongside sensitive GPS RF signal processing.","PeriodicalId":237555,"journal":{"name":"Journal of Global Positioning Systems","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125466963","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Woo Hyun Kim, Jang-Gyu Lee, H. Lee, Chan Gook Park
When GPS blockage occurs for a loosely coupled GPS/INS system, its navigation error diverges. To deal with such cases, this paper introduces an integration scheme for GPS, INS, and an image sensor. The proposed integration scheme is attractive in that it accomplished the position and velocity accuracy improvement by the angular information only. The angular information is provided by the gimbal angles of the image sensor. A realistic scenario is studied by a simulation to demonstrate that the GPS/INS/Image integrated navigation system works effectively.
{"title":"GPS/INS/Seeker Integrated Navigation System for the Case of GPS Blockage","authors":"Woo Hyun Kim, Jang-Gyu Lee, H. Lee, Chan Gook Park","doi":"10.5081/JGPS.5.1.82","DOIUrl":"https://doi.org/10.5081/JGPS.5.1.82","url":null,"abstract":"When GPS blockage occurs for a loosely coupled GPS/INS system, its navigation error diverges. To deal with such cases, this paper introduces an integration scheme for GPS, INS, and an image sensor. The proposed integration scheme is attractive in that it accomplished the position and velocity accuracy improvement by the angular information only. The angular information is provided by the gimbal angles of the image sensor. A realistic scenario is studied by a simulation to demonstrate that the GPS/INS/Image integrated navigation system works effectively.","PeriodicalId":237555,"journal":{"name":"Journal of Global Positioning Systems","volume":"01 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130250763","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper proposes an adaptive two-stage extended Kalman filter (ATEKF) for estimation of unknown fault bias in an INS-GPS loosely coupled system. The Kalman filtering technique requires complete specifications of both dynamical and statistical model parameters of the system. However, in a number of practical situations, these models may contain parameters, which may deviate from their nominal values by unknown random bias. This unknown random bias may seriously degrade the performance of the filter or cause a divergence of the filter. The two-stage extended Kalman filter (TEKF), which considers this problem in nonlinear system, has received considerable attention for a long time. The TEKF suggested until now assumes that the information of a random bias is known. But the information of a random bias is unknown or partially known in general. To solve this problem, this paper firstly proposes a new adaptive fading extended Kalman filter (AFEKF) that can be used for nonlinear system with incomplete information. Secondly, it proposes the ATEKF that can estimate unknown random bias by using the AFEKF. The proposed ATEKF is more effective than the TEKF for the estimation of the unknown random bias. The ATEKF is applied to the INS-GPS loosely coupled system with unknown fault bias.
{"title":"Adaptive Two-Stage EKF for INS-GPS Loosely Coupled System with Unknown Fault Bias","authors":"K. Kim, Jang-Gyu Lee, Chan Gook Park","doi":"10.5081/JGPS.5.1.62","DOIUrl":"https://doi.org/10.5081/JGPS.5.1.62","url":null,"abstract":"This paper proposes an adaptive two-stage extended Kalman filter (ATEKF) for estimation of unknown fault bias in an INS-GPS loosely coupled system. The Kalman filtering technique requires complete specifications of both dynamical and statistical model parameters of the system. However, in a number of practical situations, these models may contain parameters, which may deviate from their nominal values by unknown random bias. This unknown random bias may seriously degrade the performance of the filter or cause a divergence of the filter. The two-stage extended Kalman filter (TEKF), which considers this problem in nonlinear system, has received considerable attention for a long time. The TEKF suggested until now assumes that the information of a random bias is known. But the information of a random bias is unknown or partially known in general. To solve this problem, this paper firstly proposes a new adaptive fading extended Kalman filter (AFEKF) that can be used for nonlinear system with incomplete information. Secondly, it proposes the ATEKF that can estimate unknown random bias by using the AFEKF. The proposed ATEKF is more effective than the TEKF for the estimation of the unknown random bias. The ATEKF is applied to the INS-GPS loosely coupled system with unknown fault bias.","PeriodicalId":237555,"journal":{"name":"Journal of Global Positioning Systems","volume":"16 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123069499","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In the past few years, network RTK positioning technology, especially the VRS( virtual reference stations)technology, has been widely used in some parts of China and many countries of the world. In this paper, the authors mainly discuss the principle of VRS technology with corresponding formula deduction, and give detailed descriptions of VRS corrections and virtual observations generation algorithm as well as their applications.
{"title":"VRS Virtual Observations Generation Algorithm","authors":"E. Wei, Hua Chai, Z. An, Jing-nan Liu","doi":"10.5081/JGPS.5.1.76","DOIUrl":"https://doi.org/10.5081/JGPS.5.1.76","url":null,"abstract":"In the past few years, network RTK positioning technology, especially the VRS( virtual reference stations)technology, has been widely used in some parts of China and many countries of the world. In this paper, the authors mainly discuss the principle of VRS technology with corresponding formula deduction, and give detailed descriptions of VRS corrections and virtual observations generation algorithm as well as their applications.","PeriodicalId":237555,"journal":{"name":"Journal of Global Positioning Systems","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131290937","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A reflected GPS signal is normally considered as noise (multipath). However, we believe that a reflected signal contains information about the reflecting object. Though, this information may not be useful for accurate position computation, it may help us to identify the reflecting object itself, which is a type of remote sensing. Besides, by measuring the time delay of the reflected signal, it is possible to estimate the extra path length the reflected signal has to travel. Hence, in general, the analysis of reflected signal can be used for two broad categories of altimetry and remote sensing. However, this type of analysis is rather limited with current commercial GPS receivers. We are in the process of developing a software-based GPS receiver that is capable of reflected signal analysis for remote sensing purpose. The receiver consists of multi-polarization (RHCP and LHCP) array of GPS antennas, front-end device, a PC and necessary software for signal processing. In this paper, we discuss about the system architecture and algorithms, results of reflected signal analysis observed at different places in different conditions and antenna types. Finally, we will discuss the possibility of the system for remote sensing applications using GPS signal.
{"title":"GPS Reflected Signal Analysis using Software Receiver","authors":"D. Manandhar, R. Shibasaki, H. Torimoto","doi":"10.5081/JGPS.5.1.29","DOIUrl":"https://doi.org/10.5081/JGPS.5.1.29","url":null,"abstract":"A reflected GPS signal is normally considered as noise (multipath). However, we believe that a reflected signal contains information about the reflecting object. Though, this information may not be useful for accurate position computation, it may help us to identify the reflecting object itself, which is a type of remote sensing. Besides, by measuring the time delay of the reflected signal, it is possible to estimate the extra path length the reflected signal has to travel. Hence, in general, the analysis of reflected signal can be used for two broad categories of altimetry and remote sensing. However, this type of analysis is rather limited with current commercial GPS receivers. We are in the process of developing a software-based GPS receiver that is capable of reflected signal analysis for remote sensing purpose. The receiver consists of multi-polarization (RHCP and LHCP) array of GPS antennas, front-end device, a PC and necessary software for signal processing. In this paper, we discuss about the system architecture and algorithms, results of reflected signal analysis observed at different places in different conditions and antenna types. Finally, we will discuss the possibility of the system for remote sensing applications using GPS signal.","PeriodicalId":237555,"journal":{"name":"Journal of Global Positioning Systems","volume":"42 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123754527","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The vertical profiles of electron distribution near the low and mid-geomagnetic latitudes have been investigated by the computerized tomography method using Algebraic Reconstruction Technique (ART). The slant total electron contents (STEC) data for ionospheric tomography were measured at a regional GPS reference network of nine stations that have been operated by Korea Astronomy and Space Science Institute (KASI). The results from tomographic reconstruction method are in good agreement with profiles obtained by Ionosonde near the KASI GPS stations. The electron density profiles reconstructed by the tomographic method were compared with the results from Ionosonde and IRI-2001 model. GPS tomography reconstruction
{"title":"Ionospheric Tomography using A Regional GPS Network over South Korea","authors":"Byung-Kyu Choi, Jong-Uk Park, Jong‐Kyun Chung","doi":"10.5081/JGPS.5.1.47","DOIUrl":"https://doi.org/10.5081/JGPS.5.1.47","url":null,"abstract":"The vertical profiles of electron distribution near the low and mid-geomagnetic latitudes have been investigated by the computerized tomography method using Algebraic Reconstruction Technique (ART). The slant total electron contents (STEC) data for ionospheric tomography were measured at a regional GPS reference network of nine stations that have been operated by Korea Astronomy and Space Science Institute (KASI). The results from tomographic reconstruction method are in good agreement with profiles obtained by Ionosonde near the KASI GPS stations. The electron density profiles reconstructed by the tomographic method were compared with the results from Ionosonde and IRI-2001 model. GPS tomography reconstruction","PeriodicalId":237555,"journal":{"name":"Journal of Global Positioning Systems","volume":"16 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131325411","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Receiver Autonomous Integrity Monitoring (RAIM) is a method implemented within the receiver to protect users against satellite navigation system failures. Research has shown that traditional methods for the determination of RAIM holes (i.e. places where less than five satellites are visible and available) based on spatial and temporal intervals (grids) compromise accuracy dueto the constraint of computation load. Research by the authors of this paper has addressed this and developed a new algorithm to determine RAIM holes using bounded regions instead of approximation based on grid points. This paper uses the new algorithm and proposes an area based method for the computation a RAIM satellite availability statistic based on the ratio of the total area of RAIM holes and the coverage area (regional or global area). Assessment over time is based on the interpolation using a model generated from snapshot spatial statistics at a relatively long temporal interval. Test results show that the area-based method for the calculation of the RAIM satellite availability statistic is significantly more accurate with less computational load than the traditional grid points based approach.
{"title":"An Area Computation Based Method for RAIM Holes Assessment","authors":"S. Feng, W. Ochieng, R. Mautz","doi":"10.5081/JGPS.5.1.11","DOIUrl":"https://doi.org/10.5081/JGPS.5.1.11","url":null,"abstract":"Receiver Autonomous Integrity Monitoring (RAIM) is a method implemented within the receiver to protect users against satellite navigation system failures. Research has shown that traditional methods for the determination of RAIM holes (i.e. places where less than five satellites are visible and available) based on spatial and temporal intervals (grids) compromise accuracy dueto the constraint of computation load. Research by the authors of this paper has addressed this and developed a new algorithm to determine RAIM holes using bounded regions instead of approximation based on grid points. This paper uses the new algorithm and proposes an area based method for the computation a RAIM satellite availability statistic based on the ratio of the total area of RAIM holes and the coverage area (regional or global area). Assessment over time is based on the interpolation using a model generated from snapshot spatial statistics at a relatively long temporal interval. Test results show that the area-based method for the calculation of the RAIM satellite availability statistic is significantly more accurate with less computational load than the traditional grid points based approach.","PeriodicalId":237555,"journal":{"name":"Journal of Global Positioning Systems","volume":"88 10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130771485","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper presents a method that is based on Electromagnetic Modeling (EM) technique for modelling GPS carrier phase multipath signals. A commercial software plus modules developed in-house are used for modeling and processing carrier phase multipath error parameters. Static multipath modeling experiments show that up to about 35% carrier phase errors and about 25% 3D positioning errors can be reduced.
{"title":"Estimation of GPS Carrier Phase Multipath Signals Based on Site Environment","authors":"K. Fan, X. Ding","doi":"10.5081/JGPS.5.1.22","DOIUrl":"https://doi.org/10.5081/JGPS.5.1.22","url":null,"abstract":"This paper presents a method that is based on Electromagnetic Modeling (EM) technique for modelling GPS carrier phase multipath signals. A commercial software plus modules developed in-house are used for modeling and processing carrier phase multipath error parameters. Static multipath modeling experiments show that up to about 35% carrier phase errors and about 25% 3D positioning errors can be reduced.","PeriodicalId":237555,"journal":{"name":"Journal of Global Positioning Systems","volume":"50 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2006-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115406464","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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