"Mike Jr" wrote in message
...
Tim,
The specification for the GPS Standard Positioning Service is 100
meters.
That's the SA-on value...I believe it is essentially 6 meters URE. I think
the SPS generally tells you navigation performance over the constellation,
not per-satellite ranging errors.

Some very smart and hardworking people have managed to get the
Unexplained Range Error down to .75 meters. It is this level of
service that people have come to expect and rely on from GPS. Now the
wing wants to throw this brick, the "worst performing block IIA in the
constellation", at the users and try to hide behind a 100 meter
requirement that was long ago left in the dust bins.

Calm down, Mike. First, it's a IIR(M), not a IIA. More importantly, if you
look at Tim's Figure 2, you should conclude that the average bias (error on
top of the standard noise) is the difference between his 4th-order fit
(dashed line) and the 150*(1 - cos(eta)) solid line. That error is about 0.6
meters peak. That means the typical RMS error will rise from something like
0.7 meters (typical IIR) to 0.8 meters if you RSS those two numbers; meaning
it should generally stay below 1.0 meters in real practice. So, it'll be
worse than most if not all the other IIR's (and IIR(M)'s), but better than
most of the IIA's.

Look at http://gps.afspc.af.mil/gpsoc/products/uclas_sisure.jpg to get a
sense of typical URE's.
-Marty