Indicating healthy in the broadcast navigation message

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Unformatted text preview: ver any day). At least 21 satellites in the 24 nominal plane/slot positions must be set healthy and transmitting a navigation signal with 0.98 probability (yearly averaged). The U.S. Government’s commitments for maintaining PDOP (Table 3-2) and constellation SPS SIS URE (see Section 3.3) result in support for a service availability standard as presented in Table 3-3. Table 3-3. SPS Service Availability Standard Service Availability Standard Conditions and Constraints ≥ 99% Horizontal Service Availability • 36 meter horizontal (SIS only) 95% threshold. average location • 77 meter vertical (SIS only) 95% threshold. • Defined for position solution meeting the ≥ 99% Vertical Service Availability representative user conditions and operating within average location the service volume over any 24-hour interval. • Based on using only satellites transmitting standard code and indicating “healthy” in the broadcast navigation message (subframe 1). ≥ 90% Horizontal Service Availability • 36 meter horizontal (SIS only) 95% threshold. worst-case location • 77 meter vertical (SIS only) 95% threshold. • Defined for position solution meeting the ≥ 90% Vertical Service Availability representative user conditions and operating within worst-case location the service volume over any 24-hour interval. • Based on using only satellites transmitting standard code and indicating “healthy” in the broadcast navigation message (subframe 1). Page 13 October, 2001 3.3 GPS SPS Performance Standard Service Reliability Standard The U.S Government commits to providing SPS service reliability in accordance with the following tolerances. Table 3-4. Service Reliability Standard Service Reliability Standard Conditions and Constraints ≥ 99.94% global average • 30-meter Not-to-Exceed (NTE) SPS SIS URE. • Standard based on a measurement interval of one year; average of daily values within the service volume. • Standard based on 3 service failures per year, lasting no more than 6 hours each. ≥ 99.79% worst case single point • 30-meter NTE SPS SIS URE. average • Standard based on a measurement interval of one year; average of daily values from the worst-case point within the service volume. • Standard based on 3 service failures per year, lasting no more than 6 hours each. The probability of Hazardously Misleading Information (HMI) shall be less than 0.002. A HMI event occurs when the SIS URE is greater than 30 meters while the satellite is set healthy but the User Range Accuracy (URA) multiplied out to 4.42 standard deviations is less than 30 meters. 3.4 Accuracy Standard The U.S. Government commits to providing SPS SIS User Range Errors (UREs) in accordance with the tolerance established in Table 3-5. As indicated in Section 1.5, the U.S. Government does not directly monitor or verify SPS URE performance, but rather meets this standard through the monitoring of PPS UREs. Table 3-5. Constellation SPS SIS URE Standard SPS SIS URE Standard Condi...
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This document was uploaded on 09/26/2013.

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