Life-critical applications, such as aircraft and ship navigation,
especially in bad weather require extra precision and reliability.
Although reliability depends on a space-based part of a system, the
error detection and, to some extent, correction, is still possible on
the receiving end of the system. This is how it works
- We only need four satellites in view to obtain a position fix.
- If there are N satellites available, the receiver can generate
many different fixes, using subset of four arbitrary picked
satellites.
- If all is well, all the solutions are close to each other
(given that receiver respects proper satellite geometry
requirements).
- If one solution is outside the error tolerance, then the
receiver knows there is a problem with one of the satellites
involved in calculation.
- This satellite can be then identified and eliminated from the
calculations - all of this on the receiver.
This is called RAIM - Receiver Autonomous Integrity Monitoring |