LAAS availability assessment: the effects of augmentations and critical satellites on service availability
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LAAS availability assessment: the effects of augmentations and critical satellites on service availability

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    LAAS availability is affected by a number of factors including the number and accuracy of the ground reference receivers, the accuracy of the airborne receiver, the airfield location, the desired level of service, and the number and location of operational GPS satellites. Long-term service availability is determined by using a weighted average of the availability computed under different states of the satellite constellation. This paper builds upon previous work performed during development of the availability appendix of the RTCA SC-159 LAAS Minimum Aviation System Specification (MASPS), which evaluated the projected performance of LAAS at select locations across the United States. In this paper availability is examined over a larger geographic region, and several augmented GPS constellations of 30 to 48 satellites are evaluated applying the failure and restoration model used in previous work to weight the number of operational satellites. Other satellite augmentations to the LAAS such as geostationary, GLONASS, and Medium Earth Orbit (MEO) are evaluated to determine their improvement in availability and whether the requirements can be met for CAT I through CAT IIIb precision approach operations. The use of airport pseudolites (APLs) as an augmentation also is evaluated, including optimal placement of the APL to maximize availability. One goal of this paper is to illustrate the relative improvement in availability of each of these augmentations. This paper also addresses the issue of Continuity of Service for Performance Type 2 & 3 Service. The signal in space allocation of continuity for LAAS uses the concept of the number of critical satellites. This paper examines the implications of this concept on the availability of LAAS service.
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