Unformatted text preview: ing Node (RAAN): Equatorial angle from the celestial principal
direction to the ascending node.
Root Mean Square (RMS) SIS URE: A statistic that represents instantaneous SIS URE
performance in an RMS sense over some sample interval. The statistic can be for an individual
satellite or for the entire constellation. The sample interval for URE assessment used in the SPS
Performance Standard is 24 hours. Page B-2 October 2001 GPS SPS Performance Standard Selective Availability: Protection technique formerly employed to deny full system accuracy to
unauthorized users. SA was discontinued effective midnight May 1, 2000.
Service Availability: Defined to be the percentage of time over any 24-hour interval that the
predicted 95% positioning error is less than its threshold for any given point within the service
• Horizontal Service Availability: Defined to be the percentage of time over any 24-hour
interval that the predicted 95% horizontal error is less than its threshold for any point
within the service volume. • Vertical Service Availability: Defined to be the percentage of time over any 24-hour
interval that the predicted 95% vertical error is less than its threshold for any point within
the service volume. Service Degradation: a condition over a time interval during which one or more SPS
performance standards are not supported.
Service Failure: A condition over a time interval during which a healthy GPS satellite’s ranging
signal exceeds the Not-to-Exceed (NTE) SPS SIS URE tolerance.
Service Reliability: The percentage of time over a specified time interval that the instantaneous
SIS SPS URE is maintained within a specified reliability threshold at any given point within the
service volume, for all healthy GPS satellites.
Service Volume: The spatial volume supported by SPS performance standards. Specifically, the
SPS Performance Standard supports the terrestrial service volume. The terrestrial service volume
covers from the surface of the Earth up to an altitude of 3,000 kilometers.
SPS Performance Envelope: The range of nominal variation in specified aspects of SPS
SPS Performance Standard: A quantifiable minimum level for a specified aspect of GPS SPS
performance. SPS performance standards are defined in Section 3.0.
SPS Ranging Signal: An electromagnetic signal originating from an operational satellite. The
SPS ranging signal consists of a Pseudo Random Noise (PRN) C/A code, a timing reference and
sufficient data to support the position solution generation process. A description of the GPS SPS
signal is provided in Section 2. The formal definition of the SPS ranging signal is provided in ICDGPS-200C.
SPS Ranging Signal Measurement: The difference between the ranging signal time of reception
(as determined by the receiver's clock) and the time of transmission derived from the navigation
signal (as defined by the satellite's clock) multiplied by the speed of light. Also known as the
SPS SIS User Range Error (URE)...
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