State operations with very low levels of range rate

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Unformatted text preview: standard C/A Code (NSC). NSC is a code sequence reserved specifically for satellite failure conditions and is meant to ensure users cannot track through a failure detected by a GPS satellite. The occurrence of transient signal behaviors in Block II and Block IIA satellites has two effects on SPS users: • Receivers can experience a loss of signal availability during the time of the outage. In most cases the effect on the receiver is far longer than the duration of the outage on the satellite. • Receivers can exhibit large code and phase jumps at the onset of the outages. Following is an analysis of behaviors for several selected days. This is intended to familiarize the GPS user with the characteristics of the behavior for various receiver types. On June 10, 1998, a double outage occurred on PRN 16 signal (the signal transitioned to nonstandard code, then returned to standard C/A, then transitioned back to non-standard code, then transitioned back to standard C/A). This event was observed with two different dual-frequency GPS receivers, although the response of each receiver differed. One receiver exhibited large spikes in code and carrier phase, while the other did not. Figure A-4-1 illustrates the anomaly’s effect on each of the two receivers. Page A-21 October 2001 GPS SPS Performance Standard Receivers A & B (dual frequency) PRN16 Range Accel Error June 10, 1998 4 Duration = 29 sec Range Accel Error (m/s/s) 3 2 Duration = 18 sec 1 0 -1 Max Separation = 55 sec -2 -3 Arcata Valley (Rcvr B) Denver (Rcvr B) Great Falls (Rcvr B) -4 -5 292475 Arcata Valley (Rcvr A) 292495 292515 292535 292555 292575 292595 292615 292635 292655 292675 292695 GPS Time of Week (s) Figure A-4-1. Dual-Frequency Receiver Response (PRN 16 Anomaly) On November 26, 1998, a single outage occurred on PRN 15. Figure A-4-2 shows the range acceleration error experienced by three different dual-frequency receivers at the time of the outage. The receivers, all of the same receiver type, exhibited a large range acceleration error at the onset of each outage, two of which have positive sense and the third negative sense. The magnitudes vary, but nearly all of them have magnitudes well over 1500 mm/s2. A separate receiver type did not exhibit a magnitude spike at either of the outages. Furthermore, in each of the outages, this receiver took longer to reacquire the signal than any of the other receiver types. Figure A-4-3 shows a six-second outage for PRN 19 on November 2, 1998, experienced by a 6channel, single-frequency receiver. The C/NO value was used to determine the timing and duration of the outages. Under normal operation, the receiver dedicates its first five channels to each tracking a single satellite signal, leaving the sixth channel to multiplex track three other signals. The multiplex track, however, is conducted by tracking only two signals per second. For example for signals X, Y, and Z, the tracking each second is represented by XY, XZ, YZ, XY, XZ, YZ, and so on...
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This document was uploaded on 09/26/2013.

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