tailieunhanh - GPS - đường dẫn quán tính và hội nhập P5

GPS Data Errors SELECTIVE AVAILABILITY ERRORS Prior to May 1, 2000, Selective Availability (SA) was a mechanism adopted by the Department of Defense (DoD) to control the achievable navigation accuracy by nonmilitary GPS receivers. In the GPS SPS mode, the SA errors were speci®ed to degrade navigation solution accuracy to 100 m (2D RMS) horizontally and 156 m (RMS) vertically. In a press release on May 1, 2000, the President of the United States announced the decision to discontinue this intentional degradation of GPS signals available to the public. . | Global Positioning Systems Inertial Navigation and Integration Mohinder S. Grewal Lawrence R. Weill Angus P. Andrews Copyright 2001 John Wiley Sons Inc. Print ISBN 0-471-35032-X Electronic ISBN 0-471-20071-9 5 GPS Data Errors SELECTIVE AVAILABILITY ERRORS Prior to May 1 2000 Selective Availability SA was a mechanism adopted by the Department of Defense DoD to control the achievable navigation accuracy by nonmilitary GPS receivers. In the GPS SPS mode the SA errors were specified to degrade navigation solution accuracy to 100 m 2D RMS horizontally and 156 m RMS vertically. In a press release on May 1 2000 the President of the United States announced the decision to discontinue this intentional degradation of GPS signals available to the public. The decision to discontinue SA was coupled with continuing efforts to upgrade the military utility of systems using GPS and supported by threat assessments which concluded that setting SA to zero would have minimal impact on United States national security. The decision was part of an ongoing effort to make GPS more responsive to civil and commercial users worldwide. The transition as seen from Colorado Springs CO. at the GPS Support Center is shown in Figure . The figure shows the horizontal and vertical errors with SA and after SA was suspended midnight GMT 8 PM EDT May 1 2000. Figure shows mean errors with and without SA with satellite PRN numbers. Aviation applications will probably be the most visible user group to benefit from the discontinuance of SA. However precision approach will still require some form of augmentation to ensure that integrity requirements are met. Even though setting SA to zero reduces measurement errors it does not reduce the need for and design of WAAS and LAAS ground systems and avionics. 103 104 GPS DATA ERRORS Fig. Pseudorange residuals with SA. Time and frequency users may see greater effects in the long term via communication systems that can realize significant future .

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