United states naval observatory usno gps time offset

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Unformatted text preview: signal reception environment, to include local terrain, multipath, local interference source effects and user platform dynamics. • Receiver signal processing characteristics, thermal noise behavior, and quality of propagation environment delay effect models. With so many factors driving the performance a user experiences, it is obvious that a single set of performance standards cannot hope to represent the service to be expected by all users. This situation is complicated even further by the fact that many factors affecting user performance are outside the control of the U.S. Government. The U.S. Government’s strategy for establishing coherent operational performance standards in the face of such complexity is as follows: 1) Formalize operational tolerances for core performance control parameters based on original GPS design criteria, current performance characteristics, and Operational Control System (OCS) operations tempo considerations. 2) Define system-level performance metrics that map the core performance control parameters through representative user assumptions into the position and time domain. 3) Define system-level operational performance standards that include only those factors that the U.S. Government controls. 4) Establish performance feedback mechanisms based on the system-level metrics to assure that operations in accordance with core performance control parameters, in fact, continue to support the performance standards. 5) Document nominal tolerances and management philosophies for core performance parameters to allow users to derive for themselves what their expectations should be for their unique application. A-1.3.2 A Brief Description of GPS SPS Performance Parameters The purpose of this section is to describe the GPS SPS performance parameters and the controls employed by the GPS Operational Control System (OCS) to manage performance against the performance standards. System behavior is defined in terms of a series of performance parameters. These parameters are statistical in nature, to acknowledge the uncertainties inherent in GPS performance. The performance parameters dealt with in this Appendix are service availability, service reliability, and accuracy. The characteristics of each of these parameters must be considered to completely define the GPS civil performance envelope. A-1.3.2.1 Service Availability In previous documents, service availability was defined in terms of the percentage of time constellation geometry provides a Position Dilution of Precision (PDOP) of six or less. Service availability is inherently a predictive quantity, since it establishes an expectation of system performance rather than actual instantaneous behavior. The new definition for service availability includes not only the constellation geometry, but also the predicted URE contribution to user performance. Conceptually, the new definition says that the combination of constellation geometry and URE have to remain below a specified toleran...
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This document was uploaded on 09/26/2013.

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