Time to Alert the time to alert is described as the time from the onset od – MSI until an alert indication reaches the receiver’s antenna. This alert could be an alarm or a warning. Tolerance for a healthy SPS SIS is said to be SIS URE NTE Tolerance – +- 4.42 times the upper bound on the URA value corresponding to the URA index that is being broadcast by the satellite. Alert (Alarm indication) When the SPS SIS status is healthy or – marginal becomes unhealthy when it is the subject of a SPS SIS alarm indication. Presence of any of the nine alarm indicators listed below, indicates the information provided by the SPS SIS may not be correct. SPS becomes untraceable. Ceases transmission Elimination of the standard C/A-code. Substitution of non-standard C/A- code for standard Substitution of PRN C/A-code number 37 for the standard C/A-code. Failure of parity on 5 successive words of NAV data (3 seconds). Broadcast IODE does not match the 8 LSBs of the broadcast Index of Data Clock (IODC). Transmitted bits in sub-frame 1, 2, or 3 are set to 0’s or all set to 1’s. Default NAV data is being transmitted in sub-frames 1,2 or 3. 8-bit preamble does not equal 10001011, decimal 139, or hexadecimal 8B. When the SPS SIS status is healthy and it Alert (Warning Indications) - becomes marginal or unhealthy when subject of a warming indication is. Warnings are typically contributing in advance of the onset of potential MSI events. Warnings are also common after an alarm and at satellite’s end of life. Next we will be discussing the SPS SIS continuity. For the continuity, the health is a probability that the SPS SIS continues to be healthy without unscheduled interruptions over a specified time interval. Interruptions that are schedule, are announced at 48 hours in advance do not contribute to a loss of continuity. Scheduled interruptions are announced by the Control Segment issuing a “Notice Advisory to Navstar Users” (NANU). NANU’s are very similar to the to “Notices Airmen” regarding the scheduled interruptions of the ground-based air navigation aids.
Time to Alert – the time to alert is described as the time from the onset od MSI until an alert indication reaches the receiver’s antenna. This alert could be an alarm or a warning. SIS URE NTE Tolerance – Tolerance for a healthy SPS SIS is said to be +- 4.42 times the upper bound on the URA value corresponding to the URA index that is being broadcast by the satellite. Alert (Alarm indication) – When the SPS SIS status is healthy or marginal becomes unhealthy when it is the subject of a SPS SIS alarm indication. Presence of any of the nine alarm indicators listed below, indicates the information provided by the SPS SIS may not be correct. SPS becomes untraceable. Ceases transmission Elimination of the standard C/A-code. Substitution of non-standard C/A- code for standard Substitution of PRN C/A-code number 37 for the standard C/A-code. Failure of parity on 5 successive words of NAV data (3 seconds). Broadcast IODE does not match the 8 LSBs of the broadcast Index of Data Clock (IODC). Transmitted bits in sub-frame 1, 2, or 3 are set to 0’s or all set to 1’s. Default NAV data is being transmitted in sub-frames 1,2 or 3. 8-bit preamble does not equal 10001011, decimal 139, or hexadecimal 8B. Alert (Warning Indications) - When the SPS SIS status is healthy and it becomes marginal or unhealthy when subject of a warming indication is. Warnings are typically contributing in advance of the onset of potential MSI events. Warnings are also common after an alarm and at satellite’s end of life. Next we will be discussing the SPS SIS continuity. For the continuity, the health is a probability that the SPS SIS continues to be healthy without unscheduled interruptions over a specified time interval. Interruptions that are schedule, are announced at 48 hours in advance do not contribute to a loss of continuity. Scheduled interruptions are announced by the Control Segment issuing a “Notice Advisory to Navstar Users” (NANU). NANU’s are very similar to the “Notices to Airmen” regarding the scheduled interruptions of the ground-based air navigation aids.