Paired overbounding for nonideal LAAS and WAAS error distributions

A significant challenge in fielding space-based and ground-based augmentation systems (SBAS and GBAS) for GPS involves the validation of navigation integrity, which requires the establishment of error bounds for aircraft position. This paper introduces a new approach to validating position-domain integrity by using two-sided envelopes for each ranging source. This paired-bounding approach allows for error distributions of arbitrary form and thus improves on earlier integrity validation approaches restricted to zero-mean, symmetric, and unimodal distributions     

Formulation of a time-varying maximum allowable error for ground-based augmentation systems

Ground-based augmentation systems (GBAS), such as the federal aviation administration's local area augmentation system (LAAS), protect GPS users against signal anomalies by monitoring for rare satellite faults. This paper introduces a new, time-varying MERR (maximum-allowable error in range) formulation that enables proof of integrity for ground-based fault monitoring. The time-varying MERR supersedes earlier MERR methods which relied on a static integrity test. The utility of these earlier methods was limited in that they neglected GBAS time-to-alert (TTA) requirements and restricted the choice of the monitor filter, requiring its impulse response to match that of the user ranging-error filter. By contrast, the time-varying MERR explicitly incorporates TTA and places no restrictions on monitor filter design. These attributes are critical for correctly evaluating system integrity and for crediting the integrity benefits of GBAS systems with aggressive filter designs and process timing.