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

Michael O’Connor, Thomas Bell, Gabriel Elkaim, and Bradford Parkinson,

BIOGRAPHY for CDGPS initialization. In this work, the use of a single pseudolite for CDGPS initialization was explored in Michael O’Connor is a Ph.D. candidate in simulation and demonstrated experimentally on a farm and Astronautics at Stanford University. He received his tractor. B.S. in Aeronautics and Astronautics from MIT in 1992 and his M.S. from Stanford in 1993. Three aspects in particular were explored: the relationship between vehicle path geometry and navigation system Thomas Bell is a M.S. student in Aeronautics and accuracy, the mathematics of incorporating a ground Astronautics at Stanford University. He received his B.S. constraint into the carrier phase equations, and the in Mechanical Engineering from Cornell University in benefits and difficulties of using a dipole antenna to 1991, and will receive his M.S. in 1997. transmit the GPS signal to standard patch antennas.

Gabriel Elkaim is a Ph.D. candidate in Aeronautics and INTRODUCTION Astronautics at Stanford University. He received his B.S. in Aerospace Engineering from Princeton University in A low-cost, real-time precision navigation system has 1990 and his M.S. from Stanford in 1995. numerous applications in land vehicles such as data collection, driver guidance, and automatic control. Bradford Parkinson, Ph.D., is a professor of Aeronautics and Astronautics at Stanford University, and Program A large market for GPS data collection systems in land Manager of the Relativity Gyroscope Experiment vehicles is the farming industry. Meter-level code- (). He served for six years as the first differential GPS techniques are currently used for Program Director of the GPS Joint Program Office, and mapping and yield monitoring [l-3], and the use of has been instrumental in GPS program development. Dr. CDGPS for field topographic mapping has been explored Parkinson heads the NASA Advisory Council. [41.

ABSTRACT Another use for real-time centimeter-level positioning is human driver guidance. Snowplowing runways during Real-time centimeter-level positioning using carrier phase limited visibility, precise agricultural spraying, and differential GPS (CDGPS) has countless applications in increased use of tape irrigation in agriculture are just a land vehicles. Automobiles, aircraft on taxiways, few cases where driver-assisted guidance would make construction equipment, and farm tractors are just a few difficult tasks easier. types of the vehicles that could benefit from a reliable, accurate sensor producing high-bandwidth position Automatic control of land vehicles is not a new idea, but measurements. previous attempts have been limited by high cost, complexity [5-61, or dependence on vision systems [7-81. Most CDGPS systems currently available are initialized CDGPS offers the potential for low-cost precision using integer search techniques, techniques which have navigation that does not require specific external cues for some fundamental limitations. A second initialization successful operation. Robot vehicles using this technique created for precision aircraft landing uses two technology may someday be used to clear minefields, or more GPS pseudo- (“pseudolite”) transmitters

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