Effects of Multipath Reception on GPS Positioning Performance

GPS satellite broadcasting signals are subject to reflection and diffraction like any other type of electromagnetic waves. Multipath error results from interference between two radio waves which have travelled paths of different lengths between the transmitter and the receiver. GPS multipath is caused by the reception of signals arrived not only directly from satellites, but also reflected or diffracted from the local objects. Multipath results in an error in pseudorange measurements and thus affects the positioning accuracy, since the multipath signal takes a longer path than the direct signal. To verify the effects of multipath propagation on positioning performance, an experiment was conducted under controlled conditions. The specific location for the experiment was chosen, to allow controlled geometry of the reflective surface, antenna position and the critical satellite positions eventually causing multipath effects. During the 24 hour period, specific intervals were selected when multipath could be present, and the positioning performance was analyzed. The result of our experiment showed the degradation of positioning performance when multipath signals were present, causing shift of the calculated position.