A Local Positioning System for Autonomous Robot guidance aid is proposed, based on the principles of GPS, but being the emitter placed on the Robot(s) and the detectors placed in the environment. The emitted signal is an infrared laser signal ASK-modulated with a Pseudo-Random Sequence. Auto-correlation is performed at a central node. Distances to the reference points are computed in terms of differential phase shift measurements. Using m-sequence-codes makes multiemission-working conditions possible. High precision is achieved as it is shown in a final table.