Using GPS to enhance digital radio telemetry

The precise time available from the atomic clocks orbiting the earth in GPS satellites is used in many systems where time synchronization is important. The satellite clocks are monitored and adjusted by ground based control telemetry to within one microsecond of Universal Time. A number of commercial GPS receivers have the ability to provide a time synchronised output, typically one pulse per second, that is locked to this precise time base. This easily accessible timing source is often the justification for including a GPS receiver as an integral component of a complex system. There are additional benefits to be gained from integrating a GPS receiver as an embedded component of a mobile radio telemetry system, where GPS information can also be used to enhance the overall performance. This paper examines some research into combining some transmission techniques with time synchronisation from GPS receivers located in the mobile and in the base equipment to improve a digital radio channel. Using this combined approach, a reverse data channel can be eliminated where a single direction data stream is the predominant requirement.