report of the action team on global navigation satellite systems (gnss)

Table 1-4. Service Reliability StandardService Reliability StandardConditions and Constraints≥ 99.94% global average. • 30-meter Not-to-Exceed (NTE) SPSSIS URE.• Standard based on a measurementinterval <strong>of</strong> one year; average <strong>of</strong> dailyvalues within <strong>the</strong> service volume.• Standard based on 3 service failuresper year, lasting no more than 6 hourseach.≥ 99.79% worst case single point average. • 30-meter NTE SPS SIS URE.• Standard based on a measurementinterval <strong>of</strong> one year; average <strong>of</strong> dailyvalues from <strong>the</strong> worst case point within<strong>the</strong> service volume.• Standard based on 3 service failuresper year, lasting no more than 6 hourseach.43. The probability <strong>of</strong> Hazardously Misleading Information (HMI) shall be less than 0.002. AHMI event occurs when <strong>the</strong> SIS URE is greater than 30 meters, while <strong>the</strong> satellite is set healthybut <strong>the</strong> User Range Accuracy (URA) multiplied out to 4.42 standard deviations is less than 30meters.Accuracy Standard44. The United States Government commits to providing SPS SIS User Range Errors (UREs)in accordance with <strong>the</strong> tolerance established in Table 1-5. The United States Government doesnot directly monitor or verify SPS URE performance, but ra<strong>the</strong>r meets this standard through <strong>the</strong>monitoring <strong>of</strong> PPS UREs.Table 1-5. Constellation SPS SIS URE StandardSPS SIS URE Standard≤ 6 meters RMS SIS SPS URE across <strong>the</strong>entire constellation.Conditions and Constraints• Average <strong>of</strong> <strong>the</strong> constellation’sindividual satellite SPS SIS RMS UREvalues over any 24-hour interval, forany point within <strong>the</strong> service volume.45. The United States Government does not intend to impose range rate or range accelerationerrors on <strong>the</strong> SPS signal.46. The United States Government’s commitments for maintaining PDOP (Table 1-2) andconstellation SPS SIS URE (Table 1-5) result in support for position and time transfer accuracystandards as presented in Table 1-6. These accuracy standards were established based on <strong>the</strong>worst two <strong>of</strong> 24 satellites being removed from <strong>the</strong> constellation and a 6-meter constellation RMSSIS URE.13