Initial Assessment of Precision Approach Guidance Quality

摘要

A methodology for assessing the impact of jamming and anti-jam (AJ) technology on the guidance quality of a precision aircraft landing system is presented. The approach has two distinct components. The first component assesses the performance of the AJ processing; capturing characteristics required for evaluation of system level guidance quality. The second component incorporates these AJ characterizations in the determination of precision aircraft landing system guidance quality. This first order analysis is geared toward getting early results to establish the relative significance of jamming and anti-jam technology. The paper clearly describes simplifying assumptions and their impact as well as providing suggestions for increased fidelity models. Results based on these simple models show the impact of jamming and anti-jam technology on guidance quality. The first step evaluates space-time adaptive processing (STAP) performance for a given threat description, producing a carrier-to-noise-density (C/N{sub}0) skymap. An C/N{sub}0 skymap portrays the C/N{sub}0 at a GPS receiver as a function of satellite azimuth and elevation angle. The C/N{sub}0 skymap approach allows the jammer threat, and AJ response to be determined independent of the latitude and longitude of the landing. In this way, a set of C/N{sub}0 skymaps can be used to assess guidance quality at any landing site. Guidance quality is based on an extension of availability as defined in RTCA DO-245 for LAAS, and is determined as a function of accuracy, integrity and continuity. As the constellation cycles, the satellites available for navigation are culled based on (1) elevation mask, (2) C/N{sub}0 loss-of-lock failure as determined by the anti-jam C/N{sub}0 skymap, (3) differential requirement for simultaneous air and ground satellite visibility, and (4) satellite faults. The remaining "visible" satellites are then used to calculate vertical and lateral accuracy, and the vertical and lateral alarm limits used in the determination of availability. This two-step approach allows parametric studies based on the state-5 loss-of-lock threshold assumption, satellite fault models, integrity risk, number of satellites in the constellation, jammer configurations and strengths, and anti-jam technology. This first order study was geared toward early identification of the impact that jamming and AJ have on guidance quality. A simple (optimistic) model followed by successively refined, greater fidelity models allows early identification of critical aspects allowing appropriate attention to be focused on critical issues.