RAIM Algorithms - Revision history

Filipe.Pelica: Included editor logo.

2014-09-18T17:11:21Z

Included editor logo.

← Older revision		Revision as of 17:11, 18 September 2014
Line 4:		Line 4:
	\|Level=Basic		\|Level=Basic
	\|YearOfPublication=2011		\|YearOfPublication=2011
			\|Logo=GMV
	\|Title={{PAGENAME}}		\|Title={{PAGENAME}}
	}}		}}

Carlos.Lopez at 11:40, 23 February 2012

2012-02-23T11:40:25Z

← Older revision		Revision as of 11:40, 23 February 2012
Line 1:		Line 1:
	{{Article Infobox2		{{Article Infobox2
	\|Category=Fundamentals		\|Category=Fundamentals
	\|~~Authors~~=GMV		\|Editors=GMV
	\|Level=Basic		\|Level=Basic
	\|YearOfPublication=2011		\|YearOfPublication=2011
	~~\|Logo=GMV~~
	\|Title={{PAGENAME}}		\|Title={{PAGENAME}}
	}}		}}

Rui.Pereira at 17:50, 8 November 2011

2011-11-08T17:50:00Z

← Older revision		Revision as of 17:50, 8 November 2011
Line 1:		Line 1:
	{{Article Infobox2		{{Article Infobox2
	\|Category=Fundamentals		\|Category=Fundamentals
	~~\|Title={{PAGENAME}}~~
	\|Authors=GMV		\|Authors=GMV
	\|Level=Basic		\|Level=Basic
	\|YearOfPublication=2011		\|YearOfPublication=2011
	\|Logo=GMV		\|Logo=GMV
			\|Title={{PAGENAME}}
	}}		}}

	Although conventional RAIM approaches highly improve the receiver’s capacity to detect large errors, their protection levels are not able to cover all user requirements. As an example, the civil aviation community imposes more stringent alert limits whereas [[Criticality of GNSS Applications\|Liability Critical Applications]] rather focus on higher availabilities. Dedicated RAIM algorithms need to be considered according to the application at hand.		Although conventional RAIM approaches highly improve the receiver’s capacity to detect large errors, their protection levels are not able to cover all user requirements. As an example, the civil aviation community imposes more stringent alert limits whereas [[Criticality of GNSS Applications\|Liability Critical Applications]] rather focus on higher availabilities. Dedicated RAIM algorithms need to be considered according to the application at hand.

Line 21:		Line 20:

	==Conventional RAIM==		==Conventional RAIM==
	Key Features of [[~~Work in Progress:~~RAIM Fundamentals\|traditional RAIM Algorithms]]:		Key Features of [[RAIM Fundamentals\|traditional RAIM Algorithms]]:
	# Basic hypothesis: only one satellite is “faulty”, probability of multiple satellite failures at the same time is considered negligible,		# Basic hypothesis: only one satellite is “faulty”, probability of multiple satellite failures at the same time is considered negligible,
	# Number of satellites in view determines the possibility of providing integrity,		# Number of satellites in view determines the possibility of providing integrity,
Line 82:		Line 81:
	==Related articles==		==Related articles==
	*[[Integrity]]		*[[Integrity]]
	*[[~~Work in Progress:~~RAIM\|RAIM]]		*[[RAIM\|RAIM]]
	*[[~~Work in Progress:~~RAIM Fundamentals\|RAIM Fundamentals]]		*[[RAIM Fundamentals\|RAIM Fundamentals]]
	*[[~~Work in Progress:~~ARAIM\|ARAIM]]		*[[ARAIM\|ARAIM]]

Rui.Pereira: moved Work in Progress:RAIM Algorithms to RAIM Algorithms

2011-07-29T22:21:46Z

moved Work in Progress:RAIM Algorithms to RAIM Algorithms

← Older revision	Revision as of 22:21, 29 July 2011
(No difference)

Teresa.Ferreira at 14:49, 23 July 2011

2011-07-23T14:49:24Z

← Older revision		Revision as of 14:49, 23 July 2011
Line 47:		Line 47:

	Algorithms that use past measurements are also called “sequential algorithms” in the literature, as opposed to “snapshot algorithms” that use measurements from a single epoch.		Algorithms that use past measurements are also called “sequential algorithms” in the literature, as opposed to “snapshot algorithms” that use measurements from a single epoch.

			==Solution Separation RAIM==
			The maximum solution separation method <ref> Brown R. G., P. McBurney, “Self-Contained GPS Integrity Check Using Maximum Solution Separation”, Navigation: Journal of the Institute of navigation, Vol. 35, No. 1, Spring 1988 </ref> is based on the observed separation between the position estimate generated by a full-set filter (using all the satellite measurements) and that generated by each one of the subset filters (each using all but one of the satellite measurements).

			These techniques can be further extended to include multiple hypotheses. Multiple Hypothesis Solution Separation (MHSS)<ref>An Optimized Multiple Hypothesis RAIM Algorithm for Vertical Guidance, Juan Blanch, Alex Ene, Todd Walter, Per Enge, Stanford University, 2007</ref> is a RAIM technique that comprises a protection level computation procedure that admits K simultaneous faulty measurements. MHSS may or may not be accompanied by a fault detection/exclusion (FDE) mechanism. If a FDE mechanism is present, it should be triggered right before the navigation solution and its associated MHSS protection level are computed, and the said computation should use only those measurements that have passed the FDE test successfully.

			If the assumption that no more than K measurements can be faulty at the same time is correct, then all faulty measurements (if any) must have been excluded from some of the solutions previously computed, and hence the associated fault-free protection level contains the actual position with its prescribed probability. Thus the region covered by all computed solutions and their protection levels contains the actual position with the prescribed (actually higher) probability. In order to provide a unique navigation solution and an associated protection level, the all-in-view solution (the one using all N measurements) is provided, and the protection level is defined as the minimum circle around it (defined by its radius) such that all other positions together with their associated protection levels are contained within.


	==Absolute RAIM==		==Absolute RAIM==
	Absolute RAIM is an extension of the conventional RAIM algorithms, based on Multiple Hypotheses Solution Separation, MHSS (~~described below~~) <ref name="GEAS_I"></ref>.		Absolute RAIM is an extension of the conventional RAIM algorithms, based on Multiple Hypotheses Solution Separation, MHSS (see previous section) <ref name="GEAS_I"></ref>.

	The proposed Absolute RAIM technique focuses on receiver autonomy, putting the less stringent requirements on the ground segment. In fact, Absolute RAIM needs very limited external information, such as User Range Accuracies (URA) for each satellite, at low latencies (e.g. 1 hour). Another advantage of Absolute RAIM is the possibility to relax the integrity requirement for the ground segment by assigning the remaining component to the on-board algorithm. In addition, absolute RAIM greatly benefits from multiple GNSS systems since its main limitation relies on the geometry and satellite availability (linked to the high level of autonomy). Finally, accuracy requirements are covered by using dual frequency measurements to remove the ionospheric errors, leading to smaller position errors as compared to the GPS-L1 solution.		The proposed Absolute RAIM technique focuses on receiver autonomy, putting the less stringent requirements on the ground segment. In fact, Absolute RAIM needs very limited external information, such as User Range Accuracies (URA) for each satellite, at low latencies (e.g. 1 hour). Another advantage of Absolute RAIM is the possibility to relax the integrity requirement for the ground segment by assigning the remaining component to the on-board algorithm. In addition, absolute RAIM greatly benefits from multiple GNSS systems since its main limitation relies on the geometry and satellite availability (linked to the high level of autonomy). Finally, accuracy requirements are covered by using dual frequency measurements to remove the ionospheric errors, leading to smaller position errors as compared to the GPS-L1 solution.
Line 55:		Line 63:
	ARAIM introduces the concept of an Effective Monitor Threshold (EMT), which limits all solution separation terms, i.e. if one of the terms is above EMT then an alarm is raised.		ARAIM introduces the concept of an Effective Monitor Threshold (EMT), which limits all solution separation terms, i.e. if one of the terms is above EMT then an alarm is raised.

	~~==Solution Separation RAIM==~~
	The maximum solution separation method <ref> Brown R. G., P. McBurney, “Self-Contained GPS Integrity Check Using Maximum Solution Separation”, Navigation: Journal of the Institute of navigation, Vol. 35, No. 1, Spring 1988 </ref> is based on the observed separation between the position estimate generated by a full-set filter (using all the satellite measurements) and that generated by each one of the subset filters (each using all but one of the satellite measurements).

	These techniques can be further extended to include multiple hypotheses. Multiple Hypothesis Solution Separation (MHSS)<ref>An Optimized Multiple Hypothesis RAIM Algorithm for Vertical Guidance, Juan Blanch, Alex Ene, Todd Walter, Per Enge, Stanford University, 2007</ref> is a RAIM technique that comprises a protection level computation procedure that admits K simultaneous faulty measurements. MHSS may or may not be accompanied by a fault detection/exclusion (FDE) mechanism. If a FDE mechanism is present, it should be triggered right before the navigation solution and its associated MHSS protection level are computed, and the said computation should use only those measurements that have passed the FDE test successfully.

	If the assumption that no more than K measurements can be faulty at the same time is correct, then all faulty measurements (if any) must have been excluded from some of the solutions previously computed, and hence the associated fault-free protection level contains the actual position with its prescribed probability. Thus the region covered by all computed solutions and their protection levels contains the actual position with the prescribed (actually higher) probability. In order to provide a unique navigation solution and an associated protection level, the all-in-view solution (the one using all N measurements) is provided, and the protection level is defined as the minimum circle around it (defined by its radius) such that all other positions together with their associated protection levels are contained within.

	==Isotropy Based Protection Level (IBPL)==		==Isotropy Based Protection Level (IBPL)==

Teresa.Ferreira: /* Absolute RAIM */

2011-07-23T14:42:29Z

Absolute RAIM

← Older revision		Revision as of 14:42, 23 July 2011
Line 51:		Line 51:
	Absolute RAIM is an extension of the conventional RAIM algorithms, based on Multiple Hypotheses Solution Separation, MHSS (described below) <ref name="GEAS_I"></ref>.		Absolute RAIM is an extension of the conventional RAIM algorithms, based on Multiple Hypotheses Solution Separation, MHSS (described below) <ref name="GEAS_I"></ref>.

	The proposed Absolute RAIM technique focuses on receiver autonomy, putting the less stringent requirements on the ground segment. In fact, Absolute RAIM needs very limited external information, such as User Range Accuracies (URA) for each satellite, at low latencies (e.g. 1 hour). Another advantage of Absolute RAIM is the possibility to relax the integrity requirement for the ground segment by assigning the remaining component to the on-board algorithm. In addition, absolute RAIM greatly benefits from multiple GNSS systems since its main limitation relies on the geometry and satellite availability (linked to the high level of autonomy). Finally, accuracy requirements are covered by using dual frequency measurements to remove the ionospheric errors, leading to smaller position errors.		The proposed Absolute RAIM technique focuses on receiver autonomy, putting the less stringent requirements on the ground segment. In fact, Absolute RAIM needs very limited external information, such as User Range Accuracies (URA) for each satellite, at low latencies (e.g. 1 hour). Another advantage of Absolute RAIM is the possibility to relax the integrity requirement for the ground segment by assigning the remaining component to the on-board algorithm. In addition, absolute RAIM greatly benefits from multiple GNSS systems since its main limitation relies on the geometry and satellite availability (linked to the high level of autonomy). Finally, accuracy requirements are covered by using dual frequency measurements to remove the ionospheric errors, leading to smaller position errors as compared to the GPS-L1 solution.

	ARAIM introduces the concept of an Effective Monitor Threshold (EMT), which limits all solution separation terms, i.e. if one of the terms is above EMT then an alarm is raised.		ARAIM introduces the concept of an Effective Monitor Threshold (EMT), which limits all solution separation terms, i.e. if one of the terms is above EMT then an alarm is raised.

Teresa.Ferreira: /* Absolute RAIM */

2011-07-23T14:41:30Z

Absolute RAIM

← Older revision		Revision as of 14:41, 23 July 2011
Line 51:		Line 51:
	Absolute RAIM is an extension of the conventional RAIM algorithms, based on Multiple Hypotheses Solution Separation, MHSS (described below) <ref name="GEAS_I"></ref>.		Absolute RAIM is an extension of the conventional RAIM algorithms, based on Multiple Hypotheses Solution Separation, MHSS (described below) <ref name="GEAS_I"></ref>.

	The proposed Absolute RAIM technique focuses on receiver autonomy, putting the less stringent requirements on the ground segment. In fact, Absolute RAIM needs very limited external information, such as User Range Accuracies (URA) for each satellite, at low latencies (e.g. 1 hour). Another advantage of Absolute RAIM is the possibility to relax the integrity requirement for the ground segment by assigning the remaining component to the on-board algorithm. In addition, absolute RAIM greatly benefits from multiple GNSS systems since its main limitation relies on the geometry and satellite availability (linked to the high level of autonomy). Finally, accuracy requirements are covered by using dual frequency measurements to remove the ~~Ionospheric~~ errors, leading to smaller position errors.		The proposed Absolute RAIM technique focuses on receiver autonomy, putting the less stringent requirements on the ground segment. In fact, Absolute RAIM needs very limited external information, such as User Range Accuracies (URA) for each satellite, at low latencies (e.g. 1 hour). Another advantage of Absolute RAIM is the possibility to relax the integrity requirement for the ground segment by assigning the remaining component to the on-board algorithm. In addition, absolute RAIM greatly benefits from multiple GNSS systems since its main limitation relies on the geometry and satellite availability (linked to the high level of autonomy). Finally, accuracy requirements are covered by using dual frequency measurements to remove the ionospheric errors, leading to smaller position errors.

	ARAIM introduces the concept of an Effective Monitor Threshold (EMT), which limits all solution separation terms, i.e. if one of the terms is above EMT then an alarm is raised.		ARAIM introduces the concept of an Effective Monitor Threshold (EMT), which limits all solution separation terms, i.e. if one of the terms is above EMT then an alarm is raised.

Teresa.Ferreira: /* Relative RAIM (RRAIM) */

2011-07-23T14:39:03Z

Relative RAIM (RRAIM)

← Older revision		Revision as of 14:39, 23 July 2011
Line 43:		Line 43:

	Each source can be defined by a Gaussian distribution with a sigma characteristic value, which can be provided a-priori by the GNSS system. RRAIM concept shares the integrity burden between the aircraft, the GNSS constellation and the external monitors which provide the a-priori set of validated measurements.		Each source can be defined by a Gaussian distribution with a sigma characteristic value, which can be provided a-priori by the GNSS system. RRAIM concept shares the integrity burden between the aircraft, the GNSS constellation and the external monitors which provide the a-priori set of validated measurements.
	RRAIM propagates both the position and the protection levels.		As defined in <ref name="GEAS_I"></ref>, RRAIM propagates both the position and the protection levels and it is based on ionosphere-free and carrier-smoothed pseudoranges.

Teresa.Ferreira: /* Isotropy Based Protection Level (IBPL) */

2011-07-23T14:30:25Z

Isotropy Based Protection Level (IBPL)

← Older revision		Revision as of 14:30, 23 July 2011
Line 66:		Line 66:
	The IBPL autonomous technique computes Protection Levels (PL) based on error isotropy, adapting in real-time to ranging error size and considering multiple fault conditions<ref>”Autonomous Integrity – An Error Isotropy-Based Approach for Multiple Fault Conditions”, M. Azaola, J. Cosmen, InsideGNSS 2009, http://www.insidegnss.com/auto/janfeb09-azaoli.pdf</ref>.		The IBPL autonomous technique computes Protection Levels (PL) based on error isotropy, adapting in real-time to ranging error size and considering multiple fault conditions<ref>”Autonomous Integrity – An Error Isotropy-Based Approach for Multiple Fault Conditions”, M. Azaola, J. Cosmen, InsideGNSS 2009, http://www.insidegnss.com/auto/janfeb09-azaoli.pdf</ref>.
	The main challenge in designing an algorithm for LCA relies in the fact that these applications mostly operate in urban environments, which often have low satellite visibility and large measurement errors caused by Non Line Of Sight (NLOS) signal multipath components.		The main challenge in designing an algorithm for LCA relies in the fact that these applications mostly operate in urban environments, which often have low satellite visibility and large measurement errors caused by Non Line Of Sight (NLOS) signal multipath components.
	IBPL computes PL based on the all-in-view least squares solution, using the vector of LS estimation residuals as a characterization of the position error: the larger the residual vector, the larger the state estimation error vector (from a statistical perspective).		IBPL computes PL based on the all-in-view least squares solution, using the vector of Least Squares estimation residuals as a characterization of the position error: the larger the residual vector, the larger the state estimation error vector (from a statistical perspective).
	The protection level is computed as:		The protection level is computed as:

Teresa.Ferreira: /* Isotropy Based Protection Level (IBPL) */

2011-07-23T14:29:21Z

Isotropy Based Protection Level (IBPL)

← Older revision		Revision as of 14:29, 23 July 2011
Line 72:		Line 72:

	Where		Where
	*x stands for H or V, horizontal and vertical respectively		*x stands for H or V, horizontal and vertical respectively,
	*k is the Isotropic Confidence Ratio (ICR), a constant that relates the residual size with the state estimation error, and depends on the target confidence level and the number of measurements used for the estimation		*k is the Isotropic Confidence Ratio (ICR), a constant that relates the residual size with the state estimation error, and depends on the target confidence level and the number of measurements used for the estimation,
	*r is the least squares residual vector		*r is the least squares residual vector.

	When compared to RAIM algorithms (usually designed for civil aviation applications), the IBPL yields higher integrity availability at the cost of larger PL in urban environments, but also showed great availability in open sky conditions. The advantage of IBPL techniques is that they are completely autonomous.		When compared to RAIM algorithms (usually designed for civil aviation applications), the IBPL yields higher integrity availability at the cost of larger PL in urban environments, but also showed great availability in open sky conditions. The advantage of IBPL techniques is that they are completely autonomous.