The present invention is a position-based modulation system for communications devices. The device may comprise one or more of the following features: (a) a global positioning system (GPS) receiver capable of receiving positioning data from GPS satellites; (b) a radio frequency (RF) transceiver having at least a first channel and a second channel; (c) a geographical information system (GIS) database of topographical data; (d) a processor capable of optimizing transceiving parameters of the RF transceiver based on the positioning data and topographical data; and (e) a bus linking the GPS receiver, RF transceiver, GIS database, and processor.