Receiver autonomous integrity monitoring (RAIM) continuously monitors and compares signals from multiple satellites to ensure GPS signal accuracy. When you fly IFR using a non-WAAS GPS as your primary navigation system you are required to do a RAIM prediction check for your route before each flight. If RAIM is predicted to be unavailable, you must use other navigation systems or delay or cancel your flight.
The WAAS system evaluates the lowest minimums available and displays the corresponding minimums in the approach mode annunciator. LNAV and LP provide lateral guidance only. LNAV/VNAV and LPV also provide an approved glide slope. LNAV+V and LP+V provide lateral guidance with an advisory glide slope.