Real-Time CDGPS Initialization for Land Vehicles Using a Single Pseudolite

Real-time centimeter-level positioning using carrier phase differential GPS (CDGPS) has countless applications in land vehicles. Automobiles, aircraft on taxiways, construction equipment, and farm tractors are just a few types of the vehicles that could benefit from a reliable, accurate sensor producing high-bandwidth position measurements. Most CDGPS systems currently available are initialized using integer search techniques, techniques which have some fundamental limitations. A second initialization technique created for precision aircraft landing uses two or more GPS pseudo-satellite (“pseudolite”) transmitters for CDGPS initialization. In this work, the use of a single pseudolite for CDGPS initialization was explored in simulation and demonstrated experimentally on a farm tractor. Three aspects in particular were explored: the relationship between vehicle path geometry and navigation system accuracy, the mathematics of incorporating a ground constraint into the carrier phase equations, and the benefits and difficulties of using a dipole antenna to transmit the GPS signal to standard patch antennas.