<<. The differential GPS system also tells the user when a satellite is
broadcasting bad data. It can be up to several hours before a satellite can
be "turned off", thus causing positional errors to unknowing users for that
time>>
This is not directly the case. The corrected pseudorange for the "bad
satellite" broadcast from the differential reference station(s) would
compensate for the error. The DGPS technique assumes that range errors for each
satellite at the reference and remote sites will be very similar. Thus, SA and
some types of ranging error can be compensated by use of DGPS. In practice, the
best solution is to use an "all in view" position computation, and check the
results of the fix using statistical testing ( F-Test and W-Test). Of course,
cheap receivers may not be able to do this!
Rob