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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
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-184.108.40.206 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.
- Fall '09