RAIM - Revision history

Filipe.Pelica: Included editor logo.

2014-09-18T17:09:21Z

Included editor logo.

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Carlos.Lopez at 11:40, 23 February 2012

2012-02-23T11:40:20Z

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	\|YearOfPublication=2011		\|YearOfPublication=2011
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Rui.Pereira at 17:47, 8 November 2011

2011-11-08T17:47:21Z

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	\|YearOfPublication=2011		\|YearOfPublication=2011
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	Civil aviation community imposes stringent requirements on the levels of precision, integrity, continuity of service and availability provided by GNSS. One of the most essential aspects relies on integrity and its impact on safety, the major driver in civil aviation. Integrity in GNSS is the capability of providing timely warnings to the user when the service should not be used. These drivers have pushed GNSS community to look for solutions that could guarantee integrity in the civil aviation domain, such as Receiver Autonomous Integrity Monitoring (RAIM).		Civil aviation community imposes stringent requirements on the levels of precision, integrity, continuity of service and availability provided by GNSS. One of the most essential aspects relies on integrity and its impact on safety, the major driver in civil aviation. Integrity in GNSS is the capability of providing timely warnings to the user when the service should not be used. These drivers have pushed GNSS community to look for solutions that could guarantee integrity in the civil aviation domain, such as Receiver Autonomous Integrity Monitoring (RAIM).

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	Basically, RAIM algorithms make use of measurements redundancy to check the relative consistency among them (by means of the residuals) and in case of detection, the most likely “failed” satellite is determined. A key assumption usually made in RAIM algorithms for civil aviation is that only one satellite may be faulty, i.e. the probability of multiple satellite failures is negligible. Another key issue related to RAIM algorithms is that one of their goals is to find measurement errors derived from non-nominal situations.		Basically, RAIM algorithms make use of measurements redundancy to check the relative consistency among them (by means of the residuals) and in case of detection, the most likely “failed” satellite is determined. A key assumption usually made in RAIM algorithms for civil aviation is that only one satellite may be faulty, i.e. the probability of multiple satellite failures is negligible. Another key issue related to RAIM algorithms is that one of their goals is to find measurement errors derived from non-nominal situations.

	Many [[~~Work in Progress:~~RAIM Algorithms\|RAIM algorithms]] follow these steps:		Many [[RAIM Algorithms\|RAIM algorithms]] follow these steps:
	*Preliminary step: Compute the navigation solution,		*Preliminary step: Compute the navigation solution,
	*Step 1: Fault detection Mechanism,		*Step 1: Fault detection Mechanism,
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	==Related articles==		==Related articles==
	*[[Integrity]]		*[[Integrity]]
	*[[~~Work in Progress:~~RAIM Fundamentals\|RAIM Fundamentals]]		*[[RAIM Fundamentals\|RAIM Fundamentals]]
	*[[~~Work in Progress:~~RAIM Algorithms\|RAIM Algorithms]]		*[[RAIM Algorithms\|RAIM Algorithms]]
	*[[~~Work in Progress:~~ARAIM\|ARAIM]]		*[[ARAIM\|ARAIM]]

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

2011-07-29T22:18:31Z

moved Work in Progress:RAIM to RAIM

← Older revision	Revision as of 22:18, 29 July 2011
(No difference)

Teresa.Ferreira: /* RAIM Concept */

2011-07-23T11:53:22Z

RAIM Concept

← Older revision		Revision as of 11:53, 23 July 2011
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	Many [[Work in Progress:RAIM Algorithms\|RAIM algorithms]] follow these steps:		Many [[Work in Progress:RAIM Algorithms\|RAIM algorithms]] follow these steps:
	*Preliminary step: Compute the navigation solution		*Preliminary step: Compute the navigation solution,
	*Step 1: Fault detection Mechanism		*Step 1: Fault detection Mechanism,
	*Step 2: Isolation of “faulty” satellites		*Step 2: Isolation of “faulty” satellites,
	*Step 3: Protection levels computation (although this step may be optional)		*Step 3: Protection levels computation (although this step may be optional).


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	Please note that when the number of satellites in view increases, the assumption that the probability of multiple satellites is negligible can be questionable.		Please note that when the number of satellites in view increases, the assumption that the probability of multiple satellites is negligible can be questionable.


	==Related articles==		==Related articles==

Teresa.Ferreira at 11:52, 23 July 2011

2011-07-23T11:52:07Z

Rui.Pereira at 16:30, 30 June 2011

2011-06-30T16:30:07Z

← Older revision		Revision as of 16:30, 30 June 2011
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	Under the GPS Standard Positioning Service (SPS) specifications, the probability of failure is approximately 10-4 per hour, whereas a number of operations require integrity risk to be bounded by 10-7 per hour<ref>Y. Lee, K. Van Dyke, B. DeCleene, J. Studenny, M. Beckmann, Summary of RTCA SC-159 GPS Integrity Working Group Activities. Navigation Vol. 43, No 3, 1996</ref>. In this context, integrity monitoring functions would have to detect failures at the level of 10-3 per hour in order to meet the civil aviation requirements.		Under the GPS Standard Positioning Service (SPS) specifications, the probability of failure is approximately 10-4 per hour, whereas a number of operations require integrity risk to be bounded by 10-7 per hour<ref>Y. Lee, K. Van Dyke, B. DeCleene, J. Studenny, M. Beckmann, Summary of RTCA SC-159 GPS Integrity Working Group Activities. Navigation Vol. 43, No 3, 1996</ref>. In this context, integrity monitoring functions would have to detect failures at the level of 10-3 per hour in order to meet the civil aviation requirements.

	Although pushed by the civil aviation community, it should be noted that the integrity concept and related algorithms have also been identified as required by other segments, such as liability critical applications<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>, e.g. [[Tolling\|road tolling]].		Although pushed by the civil aviation community, it should be noted that the integrity concept and related algorithms have also been identified as required by other segments, such as [[Criticality of GNSS Applications\|liability critical applications]]<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>, e.g. [[Tolling\|road tolling]].

Rui.Pereira at 16:05, 30 June 2011

2011-06-30T16:05:39Z

← Older revision		Revision as of 16:05, 30 June 2011
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	==Related articles==		==Related articles==
	*[[Integrity]]		*[[Integrity]]
	*[[Work in Progress:RAIM Fundamentals]]		*[[Work in Progress:RAIM Fundamentals\|RAIM Fundamentals]]
	*[[Work in Progress:RAIM Algorithms]]		*[[Work in Progress:RAIM Algorithms\|RAIM Algorithms]]
	*[[Work in Progress:ARAIM]]		*[[Work in Progress:ARAIM\|ARAIM]]

Rui.Pereira at 16:04, 30 June 2011

2011-06-30T16:04:33Z

← Older revision		Revision as of 16:04, 30 June 2011
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	Basically, RAIM algorithms make use of measurements redundancy to check the relative consistency among them (by means of the residuals) and in case of detection, the most likely “failed” satellite is determined. A key assumption usually made in RAIM algorithms for civil aviation is that only one satellite may be faulty, i.e. the probability of multiple satellite failures is negligible. Another key issue related to RAIM algorithms is that one of their goals is to find measurement errors derived from non-nominal situations.		Basically, RAIM algorithms make use of measurements redundancy to check the relative consistency among them (by means of the residuals) and in case of detection, the most likely “failed” satellite is determined. A key assumption usually made in RAIM algorithms for civil aviation is that only one satellite may be faulty, i.e. the probability of multiple satellite failures is negligible. Another key issue related to RAIM algorithms is that one of their goals is to find measurement errors derived from non-nominal situations.

	Many [[RAIM Algorithms\|RAIM algorithms]] follow these steps:		Many [[Work in Progress:RAIM Algorithms\|RAIM algorithms]] follow these steps:
	*Preliminary step: Compute the navigation solution		*Preliminary step: Compute the navigation solution
	*Step 1: Fault detection Mechanism		*Step 1: Fault detection Mechanism
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	==Related articles==		==Related articles==
	*[[Integrity]]		*[[Integrity]]
	*[[RAIM Fundamentals]]		*[[Work in Progress:RAIM Fundamentals]]
	*[[RAIM Algorithms]]		*[[Work in Progress:RAIM Algorithms]]
	*[[ARAIM]]		*[[Work in Progress:ARAIM]]

Teresa.Ferreira at 15:03, 27 May 2011

2011-05-27T15:03:34Z

← Older revision		Revision as of 15:03, 27 May 2011
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	Please note that when the number of satellites in view increases, the assumption that the probability of multiple satellites is negligible can be questionable.		Please note that when the number of satellites in view increases, the assumption that the probability of multiple satellites is negligible can be questionable.

	~~==Summary==~~
	~~Summarizing, the key features of conventional RAIM algorithms are:~~
	*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
	*Protection levels size depend on satellite geometry (DOP)
	*RAIM algorithms use code measurements


	~~Some performance considerations regarding RAIM techniques:~~
	*Integrity Risk: configured to the required value and depends on the application
	*Protection Levels (PL): if the integrity risk is configured to 10-7, the values of PLs are higher than the ones provided by a SBAS
	*Time To Alert (TTA): this concept is meaningless for conventional RAIM algorithms. If the fault detection mechanism (step 1 mentioned above) detects any failure, that measurement is not considered to obtain the position solution. That is, the alert time is zero, since the detection is immediate.

	==Related articles==		==Related articles==

← Older revision		Revision as of 11:52, 23 July 2011
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	Civil aviation community imposes stringent requirements on the levels of precision, integrity, continuity of service and availability provided by GNSS. One of the most essential aspects relies on integrity and its impact on safety, the major driver in civil aviation. Integrity in GNSS is the capability of providing timely warnings to the user when the service should not be used. These drivers have pushed GNSS community to look for solutions that could guarantee integrity in the civil aviation domain.		Civil aviation community imposes stringent requirements on the levels of precision, integrity, continuity of service and availability provided by GNSS. One of the most essential aspects relies on integrity and its impact on safety, the major driver in civil aviation. Integrity in GNSS is the capability of providing timely warnings to the user when the service should not be used. These drivers have pushed GNSS community to look for solutions that could guarantee integrity in the civil aviation domain, such as Receiver Autonomous Integrity Monitoring (RAIM).


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	Three different architectures have been proposed to provide integrity to the aviation community<ref name="ICAO Standards">ICAO Standard and Recommended Procedures (SARPS) Annex 10</ref>:		Three different architectures have been proposed to provide integrity to the aviation community<ref name="ICAO Standards">ICAO Standard and Recommended Procedures (SARPS) Annex 10</ref>:
	*SBAS		*SBAS
	The [[SBAS General Introduction\|Satellite-Based Augmentation System (SBAS)]] is a differential technique that relies on geostationary satellites to broadcast the augmentation information (e.g. corrections and integrity-related). In addition, SBAS also provides ranging capabilities, thus potentially increasing satellite availability. Being GEO satellites, SBAS coverage is limited to a regional area, e.g. EGNOS in EU or WAAS in US, and currently only supports APV I or II approaches.		The [[SBAS General Introduction\|Satellite-Based Augmentation System (SBAS)]] is a differential technique that relies on geostationary satellites to broadcast the augmentation information (e.g. corrections and integrity-related). In addition, SBAS also provides ranging capabilities, thus potentially increasing satellite availability. Being GEO satellites, SBAS coverage is limited to a regional area, e.g. EGNOS in EU or WAAS in US, and currently only supports LPV-200, APV I or II approaches.
	*GBAS		*GBAS
	[[Ground-Based Augmentation System (GBAS)\| Ground-Based Augmentation Systems (GBAS)]] provides GNSS augmentation based on local ground elements. GBAS is a differential technique in which augmentation information (e.g. corrections and integrity-related information) is transmitted to the receiver via Very High Frequency Data Broadcast (VDB) and therefore it can be used in airports (coverage of around 30 km) for CAT III operations.		[[Ground-Based Augmentation System (GBAS)\| Ground-Based Augmentation Systems (GBAS)]] provides GNSS augmentation based on local ground elements. GBAS is a differential technique in which augmentation information (e.g. corrections and integrity-related information) is transmitted to the receiver via Very High Frequency Data Broadcast (VDB) and therefore it can be used in airports (coverage of around 30 km) for CAT III operations.
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	Within ABAS, two types of techniques are envisaged<ref name="ICAO Standards"></ref>:		Within ABAS, two types of techniques are envisaged<ref name="ICAO Standards"></ref>:
	*<b>Receiver Autonomous Integrity Monitoring (RAIM)</b>, where only GNSS information is used. RAIM scheme can be included in the satellite navigation airborne equipment, either as the main source of integrity or as a back-up for alternative sources, e.g. SBAS.		*<b>Receiver Autonomous Integrity Monitoring (RAIM)</b>, where only GNSS information is used. RAIM scheme can be included in the satellite navigation airborne equipment, either as the main source of integrity or as a back-up for alternative sources, e.g. SBAS.
	*<b>Airborne Autonomous Integrity Monitoring (AAIM)</b>, where GNSS information is complemented with on-board sensors and other components		*<b>Airborne Autonomous Integrity Monitoring (AAIM)</b>, where GNSS information is complemented with on-board sensors and other components.

	==RAIM Concept==		==RAIM Concept==
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	Taking into account that the user needs to solve four unknowns (3D position and clock) from the satellites, it follows that:		Taking into account that the user needs to solve four unknowns (3D position and clock) from the satellites, it follows that:
	*4 visible satellites are not enough to provide integrity		*4 visible satellites are not enough to provide integrity,
	*5 visible satellites: if an anomaly is detected, the measurement from that specific satellite is discarded and therefore only 4 satellites are left. With only four satellites, the receiver does not have redundancy to compute the solution with different measurements and confirm that the solution is indeed correct. Therefore the receiver is able to issue a warning but not to provide integrity		*5 visible satellites: if an anomaly is detected, the measurement from that specific satellite is discarded and therefore only 4 satellites are left. With only four satellites, the receiver does not have redundancy to compute the solution with different measurements and confirm that the solution is indeed correct. Therefore the receiver is able to issue a warning but not to provide integrity,
	*6 or more satellites: the receiver is able to detect and perform the exclusion		*6 or more satellites: the receiver is able to detect and perform the exclusion.

	The more satellites in view, the more combinations of subsets of 4 satellites are available to detect potentially faulty satellites and the better the geometric observability.		The more satellites in view, the more combinations of subsets of 4 satellites are available to detect potentially faulty satellites and the better the geometric observability.