2002
Pullen, Sam, Luo, Ming, Xie, Gang, Lee, Jiyun, Phelts, R. Eric, Akos, Dennis, Enge, Per
Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, 2002.
@conference{Pullen2002,
title = {LAAS Ground Facility Design Improvements to Meet Proposed Requirements for Category II/III Operations},
author = {Sam Pullen and Ming Luo and Gang Xie and Jiyun Lee and R. Eric Phelts and Dennis Akos and Per Enge},
url = {https://www.ion.org/publications/abstract.cfm?articleID=2212},
year = {2002},
date = {2002-09-24},
booktitle = {Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002)},
pages = {1934-1947},
address = {Portland, OR},
abstract = {Stanford University has developed a Local Area Augmentation System (LAAS) ground facility prototype known as the Integrity Monitor Testbed (IMT) to demonstrate the feasibility of LAAS precision approaches under Category I conditions. While the Category I IMT is essentially complete, research on IMT algorithms continues to improve its performance so that it can eventually meet Category II/III approach requirements. To the extent possible, it is desirable to satisfy Category II/III requirements with modifications to the existing single-frequency (L1) LAAS architecture in order to provide Category II/III initial operational capability (IOC) before the second civil frequency (L5) is present on a sufficient number of GPS satellites. This will also provide a backup operational mode in a future dual- frequency LAAS if either L1 or L5 is interfered with. This paper addresses IMT improvements to detection of satellite signal deformation, code-carrier divergence monitoring of both potential satellite failures and ionosphere spatial anomalies, and position-error monitoring at a “remote” monitor receiver that is some distance away from the existing reference receiver antennas. With these relatively-limited modifications to the existing Category I LGF architecture, significant performance improvements are demonstrated. While the degree to which these improvements are sufficient depends on changes now being considered to the Category II/III requirements, we believe that, with further refinement, they will be sufficient to provide acceptable IOC and dual-frequency backup availability.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
Stanford University has developed a Local Area Augmentation System (LAAS) ground facility prototype known as the Integrity Monitor Testbed (IMT) to demonstrate the feasibility of LAAS precision approaches under Category I conditions. While the Category I IMT is essentially complete, research on IMT algorithms continues to improve its performance so that it can eventually meet Category II/III approach requirements. To the extent possible, it is desirable to satisfy Category II/III requirements with modifications to the existing single-frequency (L1) LAAS architecture in order to provide Category II/III initial operational capability (IOC) before the second civil frequency (L5) is present on a sufficient number of GPS satellites. This will also provide a backup operational mode in a future dual- frequency LAAS if either L1 or L5 is interfered with. This paper addresses IMT improvements to detection of satellite signal deformation, code-carrier divergence monitoring of both potential satellite failures and ionosphere spatial anomalies, and position-error monitoring at a “remote” monitor receiver that is some distance away from the existing reference receiver antennas. With these relatively-limited modifications to the existing Category I LGF architecture, significant performance improvements are demonstrated. While the degree to which these improvements are sufficient depends on changes now being considered to the Category II/III requirements, we believe that, with further refinement, they will be sufficient to provide acceptable IOC and dual-frequency backup availability.
2001
Normark, Per-Ludvig, Xie, Gang, Akos, Dennis, Pullen, Sam, Luo, Ming, Lee, Jiyun, Enge, Per, Pervan, Boris
Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001), Salt Lake City, UT, 2001.
@conference{Normark2001b,
title = {The Next Generation Integrity Monitor Testbed (IMT) for Ground System Development and Validation Testing},
author = {Per-Ludvig Normark and Gang Xie and Dennis Akos and Sam Pullen and Ming Luo and Jiyun Lee and Per Enge and Boris Pervan},
doi = {10.33012/2019.16788},
year = {2001},
date = {2001-09-11},
booktitle = {Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001)},
pages = {1200-1208},
address = {Salt Lake City, UT},
abstract = {The Stanford University Integrity Monitor Testbed (IMT) is a prototype of the Local Area Augmentation System (LAAS) Ground Facility (LGF). It is used to evaluate whether the LGF can meet the integrity and continuity requirements that apply to Category I precision approach. With support from the U.S. Federal Aviation Administration (FAA), Stanford University has developed IMT algorithms and has implemented them in real-time with special emphasis on automated fault diagnosis and recovery. The first generation IMT hardware was designed in the mid-1990s, and since then computer power and receiver technology has evolved significantly. Therefore, a transition has been made to a new and improved system to further development and testing for Category I precision approach and to use as a starting point for Category II/III LGF development. This paper describes the hardware and motivation behind the second-generation IMT system. One key element of the upgrade has been the development of new software to communicate with the receivers. This function, known as Signal-in-Space Receive and Decode (SISRAD), is now a modular means of integrating different receiver types, providing synchronization of receiver measurement packets, and extracting receiver measurement packets into a specified IMT data format. With these modifications, the new IMT is able to support more extensive and efficient nominal and failure testing. The upgrade has been completed, and in this paper present nominal data fault free data is presented along with how the IMT responds to a satellite clock ramp failure.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
The Stanford University Integrity Monitor Testbed (IMT) is a prototype of the Local Area Augmentation System (LAAS) Ground Facility (LGF). It is used to evaluate whether the LGF can meet the integrity and continuity requirements that apply to Category I precision approach. With support from the U.S. Federal Aviation Administration (FAA), Stanford University has developed IMT algorithms and has implemented them in real-time with special emphasis on automated fault diagnosis and recovery. The first generation IMT hardware was designed in the mid-1990s, and since then computer power and receiver technology has evolved significantly. Therefore, a transition has been made to a new and improved system to further development and testing for Category I precision approach and to use as a starting point for Category II/III LGF development. This paper describes the hardware and motivation behind the second-generation IMT system. One key element of the upgrade has been the development of new software to communicate with the receivers. This function, known as Signal-in-Space Receive and Decode (SISRAD), is now a modular means of integrating different receiver types, providing synchronization of receiver measurement packets, and extracting receiver measurement packets into a specified IMT data format. With these modifications, the new IMT is able to support more extensive and efficient nominal and failure testing. The upgrade has been completed, and in this paper present nominal data fault free data is presented along with how the IMT responds to a satellite clock ramp failure.
Pullen, Sam, Lee, Jiyun, Luo, Ming, Pervan, Boris, Chan, Fang-Cheng, Gratton, Livio
Ephemeris Protection Level Equations and Monitor Algorithms for GBAS Conference
Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001), Salt Lake City, UT, 2001.
@conference{Pullen2001,
title = {Ephemeris Protection Level Equations and Monitor Algorithms for GBAS},
author = {Sam Pullen and Jiyun Lee and Ming Luo and Boris Pervan and Fang-Cheng Chan and Livio Gratton},
url = {https://www.ion.org/publications/abstract.cfm?articleID=1852},
year = {2001},
date = {2001-09-11},
booktitle = {Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001)},
pages = {1738-1749},
address = {Salt Lake City, UT},
abstract = {One troublesome failure mode for Ground Based Augmentation Systems (GBAS) is the possibility of large discrepancies between satellite locations in space and the locations derived by the ephemeris data that they broadcast. For the Global Positioning System (GPS), nominal ephemeris errors are typically 10 meters or less, and it would take large errors (typically greater than 1 km) to be hazardous to GBAS users making precision approaches to Category I minima. Although most large errors will be detected by the GBAS ground segment Message Field Range Test, ephemeris errors orthogonal to the line-of-sight between a failed satellite and a GBAS ground station are not detectable by this simple test. To counter this possibility, RTCA has adopted new protection levels to quantify the potential impact of undetected ephemeris failures on user position errors for both precision approach and terminal area applications. These equations define position error bounds as functions of the approximate aircraft location with respect to each satellite and the GBAS ground station as well as the magnitude of the satellite orbit error detectable by the ground station. This Minimum Detectable Error (MDE) determines the "P-value" that is broadcast by the GBAS ground station for each satellite it has approved for use. Several GBAS monitor algorithms have been developed and tested for use in GBAS installations that lack SBAS coverage. One of these is a comparison between satellite positions given by the current satellite ephemeris and the ephemeris broadcast by the same satellite on its previous pass. Variants of this "YE-TE" test have been shown to support GBAS MDE's as low as 1100 meters, which will minimize the resulting impact on Category I user availability due to the ephemeris protection level equations. In addition, means of using raw measurements to initialize this monitor and to separately verify ephemerides in real-time are proposed.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
One troublesome failure mode for Ground Based Augmentation Systems (GBAS) is the possibility of large discrepancies between satellite locations in space and the locations derived by the ephemeris data that they broadcast. For the Global Positioning System (GPS), nominal ephemeris errors are typically 10 meters or less, and it would take large errors (typically greater than 1 km) to be hazardous to GBAS users making precision approaches to Category I minima. Although most large errors will be detected by the GBAS ground segment Message Field Range Test, ephemeris errors orthogonal to the line-of-sight between a failed satellite and a GBAS ground station are not detectable by this simple test. To counter this possibility, RTCA has adopted new protection levels to quantify the potential impact of undetected ephemeris failures on user position errors for both precision approach and terminal area applications. These equations define position error bounds as functions of the approximate aircraft location with respect to each satellite and the GBAS ground station as well as the magnitude of the satellite orbit error detectable by the ground station. This Minimum Detectable Error (MDE) determines the "P-value" that is broadcast by the GBAS ground station for each satellite it has approved for use. Several GBAS monitor algorithms have been developed and tested for use in GBAS installations that lack SBAS coverage. One of these is a comparison between satellite positions given by the current satellite ephemeris and the ephemeris broadcast by the same satellite on its previous pass. Variants of this "YE-TE" test have been shown to support GBAS MDE's as low as 1100 meters, which will minimize the resulting impact on Category I user availability due to the ephemeris protection level equations. In addition, means of using raw measurements to initialize this monitor and to separately verify ephemerides in real-time are proposed.
Xie, Gang, Pullen, Sam, Luo, Ming, Normark, Per-Ludvig, Akos, Dennis, Lee, Jiyun, Enge, Per, Pervan, Boris
Integrity Design and Updated Test Results for the Stanford LAAS Integrity Monitor Testbed Conference
Proceedings of the 57th Annual Meeting of The Institute of Navigation (2001), Albuquerque, NM, 2001.
@conference{Xie2001,
title = {Integrity Design and Updated Test Results for the Stanford LAAS Integrity Monitor Testbed},
author = {Gang Xie and Sam Pullen and Ming Luo and Per-Ludvig Normark and Dennis Akos and Jiyun Lee and Per Enge and Boris Pervan},
url = {https://www.ion.org/publications/abstract.cfm?articleID=908},
year = {2001},
date = {2001-06-11},
booktitle = {Proceedings of the 57th Annual Meeting of The Institute of Navigation (2001)},
pages = {681-693},
address = {Albuquerque, NM},
abstract = {The Stanford University Integrity Monitor Testbed (IMT) is a prototype of the Local Area Augmentation System (LAAS) Ground Facility (LGF) that is used to evaluate whether the LGF can meet the integrity requirements that apply to Category I aircraft precision approach. Because of the complexity of the monitoring algorithms, it is necessary to show that these requirements are met under a variety of possible failure situations. This paper explains the integrity monitor algorithms and fault-handling logic implemented in the IMT and reports the most recent nominal and failure test results with upgraded hardware. A significant fraction of the IMT code is dedicated to processing alert messages generated by different IMT monitor algorithms. Once these monitors begin flagging questionable measurements, several steps of logical reasoning and trial removals are required to determine which failed system elements are the source of the problem. This LGF function is known as "Executive Monitoring" (EXM). This paper describes in detail the EXM procedures implemented in the IMT and their role in meeting the LGF integrity and continuity requirements. For failure testing, two methods are used to inject failures into the IMT. One is to program a WelNavigate 40- channel GPS signal simulator to generate failed RF signals, which are then fed into the IMT. The other is to modify stored IMT receiver measurements collected under nominal conditions to inject failures after the fact and then have the IMT post-process these packets. Several recent results of IMT failure testing are reported. The results of these tests demonstrate that the IMT is capable of detecting and excluding failures in compliance with the LGF integrity requirements in the current LAAS Ground Facility Specification. Improved algorithms are under study to meet the much tighter requirements for Category III precision landings.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
The Stanford University Integrity Monitor Testbed (IMT) is a prototype of the Local Area Augmentation System (LAAS) Ground Facility (LGF) that is used to evaluate whether the LGF can meet the integrity requirements that apply to Category I aircraft precision approach. Because of the complexity of the monitoring algorithms, it is necessary to show that these requirements are met under a variety of possible failure situations. This paper explains the integrity monitor algorithms and fault-handling logic implemented in the IMT and reports the most recent nominal and failure test results with upgraded hardware. A significant fraction of the IMT code is dedicated to processing alert messages generated by different IMT monitor algorithms. Once these monitors begin flagging questionable measurements, several steps of logical reasoning and trial removals are required to determine which failed system elements are the source of the problem. This LGF function is known as "Executive Monitoring" (EXM). This paper describes in detail the EXM procedures implemented in the IMT and their role in meeting the LGF integrity and continuity requirements. For failure testing, two methods are used to inject failures into the IMT. One is to program a WelNavigate 40- channel GPS signal simulator to generate failed RF signals, which are then fed into the IMT. The other is to modify stored IMT receiver measurements collected under nominal conditions to inject failures after the fact and then have the IMT post-process these packets. Several recent results of IMT failure testing are reported. The results of these tests demonstrate that the IMT is capable of detecting and excluding failures in compliance with the LGF integrity requirements in the current LAAS Ground Facility Specification. Improved algorithms are under study to meet the much tighter requirements for Category III precision landings.
Lee, Jiyun, Pullen, Sam, Xie, Gang, Enge, Per
LAAS Sigma-Mean Monitor Analysis and Failure-Test Verification Conference
Proceedings of the 57th Annual Meeting of The Institute of Navigation (2001), Albuquerque, NM, 2001.
@conference{Lee2001,
title = {LAAS Sigma-Mean Monitor Analysis and Failure-Test Verification},
author = {Jiyun Lee and Sam Pullen and Gang Xie and Per Enge},
url = {https://www.ion.org/publications/abstract.cfm?articleID=909},
year = {2001},
date = {2001-06-11},
booktitle = {Proceedings of the 57th Annual Meeting of The Institute of Navigation (2001)},
journal = {Proceedings of the 57th Annual Meeting of The Institute of Navigation (2001)},
pages = {694-704},
address = {Albuquerque, NM},
abstract = {The Local Area Augmentation System (LAAS) is a ground-based differential GPS system being developed to support aircraft precision approach and landing navigation with guaranteed integrity. Stanford University has designed, implemented and tested a LAAS ground Facility (LGF) prototype, known as the Integrity Monitor Testbed (IMT), which is used to insure that the LGF meets its requirements for navigation integrity. One significant integrity risk is that the mean of the pseudorange correction error distribution becomes non- zero or that its standard deviation (sigma) grows to exceed the broadcast correction error sigma ( ópr_gnd) during LAAS operation. Real-time mean and sigma monitoring is necessary to help insure that the true error distribution is bounded by a zero-mean Gaussian distribution with the broadcast sigma value. In addition to ensuring that the error distribution based on the broadcast sigmas overbounds the true error distribution under nominal conditions, mean and sigma monitoring is needed to detect violations due to unexpected anomalies with acceptable residual integrity risk. Both mean/sigma estimation and Cumulative Sum (CUSUM) methods are useful in this respect. For sigma monitoring, estimation more rapidly detects small violations of ópr_gnd, but the ,fast-impulse-responseŠ (FIR) CUSUM variant more promptly detects significant violations that would pose a larger threat to user integrity. Based on these analytical results, mean and sigma estimation and CUSUM methods have been implemented in the IMT and have been tested under both nominal and failure conditions. Under nominal conditions, both sigma estimates and CUSUMs stay below the relevant detection thresholds for all visible satellites in the IMT datasets we have tested. In failure testing, both sigma estimation and CUSUM methods reliably detect injected sigma violations, although both methods are limited by the 200- second interval between independent B-values. Similar results were obtained in testing of the mean monitors. Overall, both methods work smoothly and predictably for sigma and mean monitoring to maintain user integrity under both nominal and failure conditions.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
The Local Area Augmentation System (LAAS) is a ground-based differential GPS system being developed to support aircraft precision approach and landing navigation with guaranteed integrity. Stanford University has designed, implemented and tested a LAAS ground Facility (LGF) prototype, known as the Integrity Monitor Testbed (IMT), which is used to insure that the LGF meets its requirements for navigation integrity. One significant integrity risk is that the mean of the pseudorange correction error distribution becomes non- zero or that its standard deviation (sigma) grows to exceed the broadcast correction error sigma ( ópr_gnd) during LAAS operation. Real-time mean and sigma monitoring is necessary to help insure that the true error distribution is bounded by a zero-mean Gaussian distribution with the broadcast sigma value. In addition to ensuring that the error distribution based on the broadcast sigmas overbounds the true error distribution under nominal conditions, mean and sigma monitoring is needed to detect violations due to unexpected anomalies with acceptable residual integrity risk. Both mean/sigma estimation and Cumulative Sum (CUSUM) methods are useful in this respect. For sigma monitoring, estimation more rapidly detects small violations of ópr_gnd, but the ,fast-impulse-responseŠ (FIR) CUSUM variant more promptly detects significant violations that would pose a larger threat to user integrity. Based on these analytical results, mean and sigma estimation and CUSUM methods have been implemented in the IMT and have been tested under both nominal and failure conditions. Under nominal conditions, both sigma estimates and CUSUMs stay below the relevant detection thresholds for all visible satellites in the IMT datasets we have tested. In failure testing, both sigma estimation and CUSUM methods reliably detect injected sigma violations, although both methods are limited by the 200- second interval between independent B-values. Similar results were obtained in testing of the mean monitors. Overall, both methods work smoothly and predictably for sigma and mean monitoring to maintain user integrity under both nominal and failure conditions.
Lee, Jiyun, Pullen, Sam, Xie, Gang, Enge, Per
LAAS Sigma-Mean Monitor Analysis and Failure-Test Verification Conference
Proceedings of the 57th Annual Meeting of The Institute of Navigation (2001), Albuquerque, NM, 2001.
@conference{Lee2001b,
title = {LAAS Sigma-Mean Monitor Analysis and Failure-Test Verification},
author = {Jiyun Lee and Sam Pullen and Gang Xie and Per Enge},
url = {https://www.ion.org/publications/abstract.cfm?articleID=909},
year = {2001},
date = {2001-06-11},
booktitle = {Proceedings of the 57th Annual Meeting of The Institute of Navigation (2001)},
pages = {694-704},
address = {Albuquerque, NM},
abstract = {The Local Area Augmentation System (LAAS) is a ground-based differential GPS system being developed to support aircraft precision approach and landing navigation with guaranteed integrity. Stanford University has designed, implemented and tested a LAAS ground Facility (LGF) prototype, known as the Integrity Monitor Testbed (IMT), which is used to insure that the LGF meets its requirements for navigation integrity. One significant integrity risk is that the mean of the pseudorange correction error distribution becomes non- zero or that its standard deviation (sigma) grows to exceed the broadcast correction error sigma ( ópr_gnd) during LAAS operation. Real-time mean and sigma monitoring is necessary to help insure that the true error distribution is bounded by a zero-mean Gaussian distribution with the broadcast sigma value. In addition to ensuring that the error distribution based on the broadcast sigmas overbounds the true error distribution under nominal conditions, mean and sigma monitoring is needed to detect violations due to unexpected anomalies with acceptable residual integrity risk. Both mean/sigma estimation and Cumulative Sum (CUSUM) methods are useful in this respect. For sigma monitoring, estimation more rapidly detects small violations of ópr_gnd, but the ,fast-impulse-responseŠ (FIR) CUSUM variant more promptly detects significant violations that would pose a larger threat to user integrity. Based on these analytical results, mean and sigma estimation and CUSUM methods have been implemented in the IMT and have been tested under both nominal and failure conditions. Under nominal conditions, both sigma estimates and CUSUMs stay below the relevant detection thresholds for all visible satellites in the IMT datasets we have tested. In failure testing, both sigma estimation and CUSUM methods reliably detect injected sigma violations, although both methods are limited by the 200- second interval between independent B-values. Similar results were obtained in testing of the mean monitors. Overall, both methods work smoothly and predictably for sigma and mean monitoring to maintain user integrity under both nominal and failure conditions.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
The Local Area Augmentation System (LAAS) is a ground-based differential GPS system being developed to support aircraft precision approach and landing navigation with guaranteed integrity. Stanford University has designed, implemented and tested a LAAS ground Facility (LGF) prototype, known as the Integrity Monitor Testbed (IMT), which is used to insure that the LGF meets its requirements for navigation integrity. One significant integrity risk is that the mean of the pseudorange correction error distribution becomes non- zero or that its standard deviation (sigma) grows to exceed the broadcast correction error sigma ( ópr_gnd) during LAAS operation. Real-time mean and sigma monitoring is necessary to help insure that the true error distribution is bounded by a zero-mean Gaussian distribution with the broadcast sigma value. In addition to ensuring that the error distribution based on the broadcast sigmas overbounds the true error distribution under nominal conditions, mean and sigma monitoring is needed to detect violations due to unexpected anomalies with acceptable residual integrity risk. Both mean/sigma estimation and Cumulative Sum (CUSUM) methods are useful in this respect. For sigma monitoring, estimation more rapidly detects small violations of ópr_gnd, but the ,fast-impulse-responseŠ (FIR) CUSUM variant more promptly detects significant violations that would pose a larger threat to user integrity. Based on these analytical results, mean and sigma estimation and CUSUM methods have been implemented in the IMT and have been tested under both nominal and failure conditions. Under nominal conditions, both sigma estimates and CUSUMs stay below the relevant detection thresholds for all visible satellites in the IMT datasets we have tested. In failure testing, both sigma estimation and CUSUM methods reliably detect injected sigma violations, although both methods are limited by the 200- second interval between independent B-values. Similar results were obtained in testing of the mean monitors. Overall, both methods work smoothly and predictably for sigma and mean monitoring to maintain user integrity under both nominal and failure conditions.