LAAS is a system installed on the ground station that allows the A/c to fly approaches in the Noise Sensitive Areas, following curved flight paths to avoid them.
It derives A/c position from the GPS satellites and comparing the same with its own precisely calculated A/c location.
It is more like having a ATC instructions giving you a Radar Vectoring to avoid Noise Sensitive Areas, except that in the case of LAAS the instructions are given in the form of visual indications on the Display panel.