last update: 2024-03-08
2006
Lee, Jiyun, Luo, Ming, Pullen, Sam, Park, Young Shin, Enge, Per, Brenner, Mats
Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006), Fort Worth, TX, 2006.
@conference{Lee2006d,
title = {Position-Domain Geometry Screening to Maximize LAAS Availability in the Presence of Ionosphere Anomalies},
author = {Jiyun Lee and Ming Luo and Sam Pullen and Young Shin Park and Per Enge and Mats Brenner},
url = {https://www.ion.org/publications/abstract.cfm?articleID=6900},
year = {2006},
date = {2006-09-26},
booktitle = {Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006)},
pages = {393 - 408},
address = {Fort Worth, TX},
abstract = {All fault modes in the Local Area Augmentation System should be mitigated within the specified integrity risk allocation to guarantee the safety of a landing aircraft. However, monitoring within the LAAS Ground Facility is insufficient to completely protect users from unacceptable errors due to ionosphere spatial gradient anomalies. A methodology has been developed to inflate the broadcast ópr_gnd and óvig so that subset satellite geometries (i.e., subsets of the set of approved GPS satellites for which the LGF broadcasts valid corrections) for which unacceptable errors are possible are made unavailable to users. The required sigma inflation factors are computed offline and are input into each LGF site during site installation. These offline simulations and the resulting inflation factors are updated periodically to insure that they remain sufficient to mitigate residual ionosphere anomaly risk. This paper describes the updated ionosphere threat space and the geometry screening algorithm required to be implemented to support the FAA/Honeywell LAAS Provably Safe Prototype (PSP) at Memphis airport. It also demonstrates by simulation results that the required availability of integrity for CAT I approaches is achievable with the proposed method.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
All fault modes in the Local Area Augmentation System should be mitigated within the specified integrity risk allocation to guarantee the safety of a landing aircraft. However, monitoring within the LAAS Ground Facility is insufficient to completely protect users from unacceptable errors due to ionosphere spatial gradient anomalies. A methodology has been developed to inflate the broadcast ópr_gnd and óvig so that subset satellite geometries (i.e., subsets of the set of approved GPS satellites for which the LGF broadcasts valid corrections) for which unacceptable errors are possible are made unavailable to users. The required sigma inflation factors are computed offline and are input into each LGF site during site installation. These offline simulations and the resulting inflation factors are updated periodically to insure that they remain sufficient to mitigate residual ionosphere anomaly risk. This paper describes the updated ionosphere threat space and the geometry screening algorithm required to be implemented to support the FAA/Honeywell LAAS Provably Safe Prototype (PSP) at Memphis airport. It also demonstrates by simulation results that the required availability of integrity for CAT I approaches is achievable with the proposed method.
Lee, Jiyun, Pullen, Sam, Enge, Per
Sigma-Mean Monitoring for the Local Area Augmentation of GPS Journal Article
In: IEEE Transactions on Aerospace and Electronic Systems, vol. 42, no. 2, pp. 625-635, 2006.
@article{Lee2006c,
title = {Sigma-Mean Monitoring for the Local Area Augmentation of GPS},
author = {Jiyun Lee and Sam Pullen and Per Enge},
doi = {10.1109/TAES.2006.1642577},
year = {2006},
date = {2006-06-19},
journal = {IEEE Transactions on Aerospace and Electronic Systems},
volume = {42},
number = {2},
pages = {625-635},
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. To quantitatively appraise navigation integrity, an aircraft computes vertical and lateral protection levels using the standard deviation of pseudo-range correction errors, /spl sigma//sub pr/spl I.bar/gnd/, broadcast by the LAAS ground facility (LGF). Thus, one significant integrity risk is that the true standard deviation (sigma) of the pseudo-range correction error distribution may grow to exceed the broadcast correction error sigma or that the true mean of the correction error distribution becomes excessive during LAAS operation. This event may occur due to unexpected anomalies of GPS measurements. To insure that the true error distribution is bounded by a zero-mean Gaussian distribution with the broadcast sigma value, real-time sigma and mean monitoring is necessary. Both direct estimation and cumulative sum (CUSUM) methods are useful to detect violations with acceptable residual integrity risk. For sigma monitoring, the estimation method more rapidly detects small violations of /spl sigma//sub pr/spl I.bar/gnd/ but the fast initial response (FIR) CUSUM variant more promptly detects significant violations that would pose a larger threat to user integrity. For the purposes of mean monitoring, the FIR CUSUM variant is superior to the estimation method in detecting any mean violations. The results demonstrate that real-time protection is achievable against all sizes of sigma/mean failures that can threaten navigation integrity.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
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. To quantitatively appraise navigation integrity, an aircraft computes vertical and lateral protection levels using the standard deviation of pseudo-range correction errors, /spl sigma//sub pr/spl I.bar/gnd/, broadcast by the LAAS ground facility (LGF). Thus, one significant integrity risk is that the true standard deviation (sigma) of the pseudo-range correction error distribution may grow to exceed the broadcast correction error sigma or that the true mean of the correction error distribution becomes excessive during LAAS operation. This event may occur due to unexpected anomalies of GPS measurements. To insure that the true error distribution is bounded by a zero-mean Gaussian distribution with the broadcast sigma value, real-time sigma and mean monitoring is necessary. Both direct estimation and cumulative sum (CUSUM) methods are useful to detect violations with acceptable residual integrity risk. For sigma monitoring, the estimation method more rapidly detects small violations of /spl sigma//sub pr/spl I.bar/gnd/ but the fast initial response (FIR) CUSUM variant more promptly detects significant violations that would pose a larger threat to user integrity. For the purposes of mean monitoring, the FIR CUSUM variant is superior to the estimation method in detecting any mean violations. The results demonstrate that real-time protection is achievable against all sizes of sigma/mean failures that can threaten navigation integrity.
Lee, Jiyun, Pullen, Sam, Enge, Per, Pervan, Boris, Gratton, Livio
Monitoring GPS Satellite Orbit Errors for Aircraft Landing Systems Journal Article
In: Journal of Aircraft, vol. 43, no. 3, pp. 799-808, 2006.
@article{Lee2006c,
title = {Monitoring GPS Satellite Orbit Errors for Aircraft Landing Systems},
author = {Jiyun Lee and Sam Pullen and Per Enge and Boris Pervan and Livio Gratton},
doi = {10.2514/1.17339},
year = {2006},
date = {2006-05-01},
journal = {Journal of Aircraft},
volume = {43},
number = {3},
pages = {799-808},
abstract = {Ground-based augmentations of the global positioning system (GPS) demand the greatest safety and reliability to support aircraft precision approach and landing navigation. One troublesome failure mode for these systems is the possibility of large orbit errors; discrepancies between the locations of GPS satellites in space and the locations derived by the ephemeris data that they broadcast. To counter this possibility, several ephemeris monitor algorithms detecting orbit errors are described. The method is based on a comparison between satellite positions given by the current satellite ephemeris [today’s ephemeris (TE)] and the ephemeris broadcast by the same satellite on its preceding pass [yesterday’s ephemeris (YE)]. Variants of this YE–TE test are shown to provide protection against ephemeris errors and also to support minimum detectable errors as low as 1145 m, which will minimize the resulting impact on ground-based augmentation system user availability. In addition, to initialize these monitors when no earlier validated ephemerides are available, means of using raw measurements are proposed. The results show that the YE–TE and the measurement-based methods together are adequate to meet navigation integrity and availability requirements for category 1 precision approaches.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Ground-based augmentations of the global positioning system (GPS) demand the greatest safety and reliability to support aircraft precision approach and landing navigation. One troublesome failure mode for these systems is the possibility of large orbit errors; discrepancies between the locations of GPS satellites in space and the locations derived by the ephemeris data that they broadcast. To counter this possibility, several ephemeris monitor algorithms detecting orbit errors are described. The method is based on a comparison between satellite positions given by the current satellite ephemeris [today’s ephemeris (TE)] and the ephemeris broadcast by the same satellite on its preceding pass [yesterday’s ephemeris (YE)]. Variants of this YE–TE test are shown to provide protection against ephemeris errors and also to support minimum detectable errors as low as 1145 m, which will minimize the resulting impact on ground-based augmentation system user availability. In addition, to initialize these monitors when no earlier validated ephemerides are available, means of using raw measurements are proposed. The results show that the YE–TE and the measurement-based methods together are adequate to meet navigation integrity and availability requirements for category 1 precision approaches.
Lee, Jiyun, Pullen, Sam, Datta-Barua, Seebany, Enge, Per
Assessment of Nominal Ionosphere Spatial Decorrelation for LAAS Conference
Proceedings of IEEE/ION PLANS 2006, San Diego, CA, 2006.
@conference{Lee2006cc,
title = {Assessment of Nominal Ionosphere Spatial Decorrelation for LAAS},
author = {Jiyun Lee and Sam Pullen and Seebany Datta-Barua and Per Enge},
doi = {10.1109/PLANS.2006.1650638},
year = {2006},
date = {2006-04-25},
booktitle = {Proceedings of IEEE/ION PLANS 2006},
pages = {506 - 514},
address = {San Diego, CA},
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. To quantitatively evaluate navigation integrity, an aircraft computes vertical and lateral protection levels as position-error bounds using integrity parameters broadcast by a nearby LAAS Ground Facility (LGF). These parameters include a standard deviation of ionosphere spatial decorrelation because the range errors introduced by the ionosphere vary between LGF receivers and LAAS users. Thus, it is necessary to estimate typical ionosphere gradients for nominal days and to determine an appropriate upper bound to sufficiently cover the differential error due to the ionosphere spatial decorrelation. In this paper, both Station-Pair and Time-Step methods are used to assess the standard deviation of vertical (or zenith) ionosphere gradients ( vig ó ). The Station-Pair method compares the simultaneous zenith delays from two different reference stations to a single satellite and observes the difference in delay across the known ionosphere pierce point (IPP) separation. Because most of these IPP separations are larger than 100 km, the Time-Step method is also used to better understand ionosphere gradients at LAAS-applicable distance scales (10 – 40 km). The Time-Step method compares the ionospheric delay of a single line-of-sight (LOS) at one epoch with the delay for the same LOS at the other epoch a short time (seconds or minutes) later. This method has the advantage of removing inter-frequency bias (IFB) calibration errors on different satellites and receivers while possibly introducing an estimation error due to temporal ionosphere gradients. This paper shows results from analyzing the post-processed ionosphere database for the Wide Area Augmentation System (WAAS), known as “supertruth”, as well as JPL post-processed data from the Continuously Operating Reference Stations (CORS) database. CORS data is adequate for the Station-Pair method because of the relatively dense CORS receiver network. However, WAAS data is of higher quality since each reference station has three high-quality receivers that aid in removing measurement outliers and reducing noise. The results of this study demonstrate that typical values of vig ó are on the order of 1 – 3 mm/km for non-stormy ionosphere conditions. As a result, a broadcast vig ó of 4 mm/km is conservative enough to bound ionosphere spatial decorrelation for nominal days with margin for more active days and for non-Gaussian tail behavior. Future work will attempt to better resolve the details of nominal ionosphere behavior over short distances as well as determine if the broadcast “bounding value” of vig ó can be reduced prior to LAAS commissioning.},
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. To quantitatively evaluate navigation integrity, an aircraft computes vertical and lateral protection levels as position-error bounds using integrity parameters broadcast by a nearby LAAS Ground Facility (LGF). These parameters include a standard deviation of ionosphere spatial decorrelation because the range errors introduced by the ionosphere vary between LGF receivers and LAAS users. Thus, it is necessary to estimate typical ionosphere gradients for nominal days and to determine an appropriate upper bound to sufficiently cover the differential error due to the ionosphere spatial decorrelation. In this paper, both Station-Pair and Time-Step methods are used to assess the standard deviation of vertical (or zenith) ionosphere gradients ( vig ó ). The Station-Pair method compares the simultaneous zenith delays from two different reference stations to a single satellite and observes the difference in delay across the known ionosphere pierce point (IPP) separation. Because most of these IPP separations are larger than 100 km, the Time-Step method is also used to better understand ionosphere gradients at LAAS-applicable distance scales (10 – 40 km). The Time-Step method compares the ionospheric delay of a single line-of-sight (LOS) at one epoch with the delay for the same LOS at the other epoch a short time (seconds or minutes) later. This method has the advantage of removing inter-frequency bias (IFB) calibration errors on different satellites and receivers while possibly introducing an estimation error due to temporal ionosphere gradients. This paper shows results from analyzing the post-processed ionosphere database for the Wide Area Augmentation System (WAAS), known as “supertruth”, as well as JPL post-processed data from the Continuously Operating Reference Stations (CORS) database. CORS data is adequate for the Station-Pair method because of the relatively dense CORS receiver network. However, WAAS data is of higher quality since each reference station has three high-quality receivers that aid in removing measurement outliers and reducing noise. The results of this study demonstrate that typical values of vig ó are on the order of 1 – 3 mm/km for non-stormy ionosphere conditions. As a result, a broadcast vig ó of 4 mm/km is conservative enough to bound ionosphere spatial decorrelation for nominal days with margin for more active days and for non-Gaussian tail behavior. Future work will attempt to better resolve the details of nominal ionosphere behavior over short distances as well as determine if the broadcast “bounding value” of vig ó can be reduced prior to LAAS commissioning.
2004
Lee, Jiyun
LAAS Position Domain Monitor Analysis and Test Results for CAT II/III Operations Conference
Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, 2004.
@conference{Lee2004,
title = {LAAS Position Domain Monitor Analysis and Test Results for CAT II/III Operations},
author = {Jiyun Lee},
url = {https://www.ion.org/publications/abstract.cfm?articleID=5962},
year = {2004},
date = {2004-09-21},
booktitle = {Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004)},
pages = {2786-2796},
address = {Long Beach, CA},
abstract = {The Local Area Augmentation System (LAAS) is a differential GPS navigation system being developed to support aircraft precision approach and landing with guaranteed accuracy, integrity, continuity and availability. While the system promises to support Category I operations, significant technical challenges are encountered in supporting Category II and III operations. The primary concern has been the need to guarantee contentment with stringent requirements for navigation availability. This paper describes how Position Domain Monitoring (PDM) may be used to improve system availability by reducing the inflation factor for standard deviations of pseudorange correction errors. The role of PDM in mitigating the continuity and integrity risks are also presented with recent test results.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
The Local Area Augmentation System (LAAS) is a differential GPS navigation system being developed to support aircraft precision approach and landing with guaranteed accuracy, integrity, continuity and availability. While the system promises to support Category I operations, significant technical challenges are encountered in supporting Category II and III operations. The primary concern has been the need to guarantee contentment with stringent requirements for navigation availability. This paper describes how Position Domain Monitoring (PDM) may be used to improve system availability by reducing the inflation factor for standard deviations of pseudorange correction errors. The role of PDM in mitigating the continuity and integrity risks are also presented with recent test results.
2003
Pullen, Sam, Lee, Jiyun, Xie, Gang, Enge, Per
CUSUM-Based Real-Time Risk Metrics for Augmented GPS and GNSS Conference
Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, 2003.
@conference{Pullen2003,
title = {CUSUM-Based Real-Time Risk Metrics for Augmented GPS and GNSS},
author = {Sam Pullen and Jiyun Lee and Gang Xie and Per Enge},
url = {https://www.ion.org/publications/abstract.cfm?articleID=5412},
year = {2003},
date = {2003-09-09},
booktitle = {Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003)},
pages = {2275-2287},
address = {Portland, OR},
abstract = {Sigma monitoring is a key component of the real-time integrity verification capability demonstrated by the Stanford University Local Area Augmentation System (LAAS) Ground Facility prototype known as the Integrity Monitor Testbed (IMT). The IMT has both sigma estimation and sigma Cumulative Sum (CUSUM) algorithms to detect small and large sigma violations, respectively. When combined with a prior probability distribution for the sigma parameter being monitored and the use of Bayes' rule, the CUSUM can provide a real-time posterior distribution of sigma based on the current CUSUM state. This paper presents the methodology for this "Bayesian CUSUM" technique and shows how it could be used to enhance integrity monitoring while better preserving continuity and availability.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
Sigma monitoring is a key component of the real-time integrity verification capability demonstrated by the Stanford University Local Area Augmentation System (LAAS) Ground Facility prototype known as the Integrity Monitor Testbed (IMT). The IMT has both sigma estimation and sigma Cumulative Sum (CUSUM) algorithms to detect small and large sigma violations, respectively. When combined with a prior probability distribution for the sigma parameter being monitored and the use of Bayes' rule, the CUSUM can provide a real-time posterior distribution of sigma based on the current CUSUM state. This paper presents the methodology for this "Bayesian CUSUM" technique and shows how it could be used to enhance integrity monitoring while better preserving continuity and availability.
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.