GPS Pseudolite Transceivers and their Applications

There are an increasing number of applications requiring precise relative position and clock offset information. The Global Positioning System has demonstrated precise and drift free position and timing information using CodeDivision-Multiple-Access (CDMA) spread spectrum technology. This technology is widely used and relatively inexpensive, making it attractive in applications beyond the scope of typical satellite based GPS. In situations with limited or no visibility of the GPS satellites, ground transmitters that emulate the signal structure of the GPS satellites (pseudolites) can be used as additional or replacement signal sources. Transceivers (which transmit and receive GPS signals) can be used to improve standard pseudolite positioning systems. If their locations are known, transceivers can be used to remove the need for the reference antenna typically necessary in standard differential systems. By using either the GPS satellite signals or other transceiver signals, a self-surveying transmitter array can be implemented, eliminating the need for a priori knowledge of pseudolite locations. In addition, transceivers mounted on vehicles can allow continuous inter-vehicle positioning without the presence of signals from GPS satellites. This paper provides an overview of the issues associated with GPS transceiver systems. This includes transceiver architectures, capabilities, and limitations. This paper also discusses several transceiver applications being studied at Stanford University including open pit mining, Mars exploration, and multiple-vehicle space-based interferometry.