OEM4 Family Installation and Operation User Manual Rev 12 154Appendix D MultipathD.1 MultipathMultipath signal reception is one of the most plaguing problems that detracts from the accuracypotential of GPS pseudorange differential positioning systems. This section will provide a brief look atthe problems of multipath reception and some solutions developed by NovAtel.Multipath occurs when an RF signal arrives at the receiving antenna from more than one propagationroute (multiple propagation paths).Figure 62: Illustration of GPS Signal MultipathD.1.1 Why Does Multipath Occur?When the GPS signal is emitted from the satellite antenna, the RF signal propagates away from theantenna in many directions. Because the RF signal is emitted in many directions simultaneously and istraveling different paths, these signals encounter various and differing natural and man-made objectsalong the various propagation routes. Whenever a change in medium is encountered, the signal iseither absorbed, attenuated, refracted, or reflected.Refraction and reflection cause the signals to change direction of propagation. This change in pathdirections often results in a convergence of the direct path signal with one or more of the reflectedsignals. When the receiving antenna is the point of convergence for these multipath signals, theconsequences are generally not favorable.Whenever the signal is refracted, some signal polarity shifting takes place; and when full reflectionoccurs, full polarity reversal results in the propagating wave. The consequences of signal polarityshifting and reversal at the receiving antenna vary from minor to significant. As well, refracted and
