Young C. Lee

Receiver autonomous integrity monitoring (RAIM) capability for sole-means GPS navigation in the oceanic phase of flight

The author analyzes GPS (Global Positioning System) RAIM capability for sole-means navigation in the oceanic phase of flight, where the position protection limit requirement for the integrity function is not as stringent as for nonprecision approaches, and yet both detection and identification functions may be required if GPS is to be used as a sole-means system. For this purpose, a novel detection and identification algorithm is developed which takes advantage of the fact that, for the oceanic phase of flight, a much larger position error is acceptable than for the nonprecision approach phase of flight. The performance of this novel algorithm and an algorithm proposed previously by others is estimated via simulation and compared. On the basis of the results, recommendations are made on how RAIM may be used if GPS is to be coupled with an inertial system to provide a sole-means capability in the oceanic phase of flight.<<ETX>>Receiver autonomous integrity monitoring (RAIM), a GPS integrity monitoring scheme that uses redundant ranging signals to detect a satellite malfunction that results in a large range error, involves two functions: detection of the presence of a malfunctioning satellite and identification of which satellite (or satellites) is malfunctioning. An analysis is presented of GPS RAIM capability for sole-means navigation in the oceanic phase of flight, where the position protection limit requirement for the integrity function is not as stringent as for nonprecision approaches, and yet both detection and identification function may be required if GPS is to be used as a sole-means system. For this purpose, a detection and identification algorithm is developed which takes advantage of the fact that for the oceanic phase of flight, a much larger position error is acceptable than for the nonprecision approach phase of flight. The performance of this algorithm and an algorithm proposed previously by others is estimated via simulation and compared. On the basis of the results, recommendations are made on how RAIM may be used if GPS is to be coupled with an inertial system to provide a sole-means capability in the oceanic phase of flight.<<ETX>>

Baseline advanced RAIM user algorithm and possible improvements

We present a baseline multiple fault and multiconstellation advanced receiver autonomous integrity monitoring user algorithm for vertical guidance. After reviewing the navigation requirements for localizer performance with vertical guidance down to 200 feet, we describe in detail how to process the pseudorange measurements, the nominal error models, and the prior fault probabilities to obtain the protection levels and other figures of merit. In particular, we show how to determine which fault modes must be monitored and a method for performing fault exclusion. Finally, we present a list of possible algorithm improvements and simplifications.

A Position Domain Relative RAIM Method

The GNSS evolutionary architecture study (GEAS) Panel was formed by the FAA in October 2006 with the objective of evaluating future GNSS-based architectures to provide robust worldwide instrument approach guidance known as LPV-200 in the 2025 to 2030 time frame. One of the architectures being considered by GEAS is based on a new concept called Relative Receiver Autonomous Integrity Monitoring (RRAIM). In this architecture, RRAIM is used with a WAAS-like system or an integrity-assured GPS III system that meets all LPV-200 requirements except for the integrity time-to-alert requirement. Such a system provides integrity but with a delay of several seconds up to a few minutes. During the period of this delay, RRAIM fills the gap as follows. User equipment estimates the change in user position by measuring accumulated carrier phase single differences of range measurements of satellites used in the position solution. Then Receiver Autonomous Integrity Monitoring (RAIM) is used to assure integrity in the change in position. Since the nominal errors associated with the carrier phase measurements are significantly smaller than those of pseudorange measurements, much tighter thresholds and thus smaller vertical protection level (VPL) can be obtained in times of relatively poor geometry, resulting in improved service availability.

A position domain relative RAIM method

The GNSS Evolutionary Architecture Study (GEAS) Panel has been evaluating future GNSS-based architectures to provide worldwide instrument approach guidance known as LPV-200 in the 2025 to 2030 time frame. One of the architectures being considered by GEAS is based on a new concept called relative receiver autonomous integrity monitoring (RRAIM). In this architecture RRAIM is implemented in aircraft and is used in conjunction with a system like the satellite-based augmentation system (SBAS), possibly with a reduced number of ground reference stations or an integrity-assured GPS III system that meets all LPV-200 requirements except for the integrity time-to-alert (TTA) requirement. RRAIM fills the time gap between the required TTA and the TTA assured by GPS III (or SBAS augmentation) by propagating the most recent integrity-assured position solution to the current time using accumulated carrier phase single differences of range measurements. RRAIM gives significantly higher service availability than can be obtained with stand-alone absolute RAIM (ARAIM). This paper develops a position domain RRAIM method with an optimization scheme that further improves LPV-200 service availability.

Ground monitoring schemes for GPS integrity channel

Issues involved in the design and implementation of the ground monitor segment Global Positioning System (GPS) are analyzed. In particular, two alternative ground monitoring schemes are presented and compared, one using classified GPS information, and the other not. For each scheme, processing functions that must be performed by the ground monitoring segment are identified, considering both the impact of selective availability on monitoring and the integrity decision concept recommended by the Global Integrity Channel (GIC) Working Group of the Radio Technical Commission for Aeronautics Special Committee-159. >

DESCRIPTION OF REQUIREMENTS ANALYSES TO SUPPORT DEVELOPMENT OF AN FAA POSITION ON USE OF GPS AS A PRIMARY MEANS OF NAVIGATION IN OCEANIC AND REMOTE SPACE.

The U. S. Federal Aviation Administration (FAA) recently investigated the use of GPS as a primary means of navigation in oceanic and remote airspace prior to the implementation of the Wide-Area Aug...