Abstract

A data/voice modem embodiment of the present invention comprises an asynchronous-to-synchronous data converter for interface with a GPS receiver, a minimum space keyed modem, and a continuous tone controlled sub-audible squelch controller that modulates a radio transceiver interface with a discrete tone such that both voice and data may share a common radio channel. The data/voice modem periodically keys-up the radio transmitter through its interface and transmits a packet of information that contains user position and velocity obtained through the GPS transceiver interface and adds a user identification code and time tag. Incoming message packets from the radio transceiver that are sent from other similarly equipped mobile units are used to supply individual network member absolute positions and velocities, and this information is stored by user identification number as goal or waypoint equivalents. As such, distance-to-goal, estimated-time-of-arrival and velocity-made-good estimates are made available on a target track screen included in the respective GPS receiver.