Multi-Antenna GPS for Improved Carrier Phase Positioning in Autonomous Convoys
Type of DegreeMaster's Thesis
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In this thesis, low-cost differential Global Positioning System (DGPS) techniques are developed for use in automated vehicle convoying. Global Positioning System (GPS) pseudorange and carrier-phase measurements are used to determine a relative position vector (RPV) between vehicles and between two antennas rigidly fixed to a vehicle in an attitude-baseline con guration. The pseudorange measurements assist in the estimation of the integer ambiguity inherent in the highly accurate, but ambiguous carrier-phase measurement necessary to achieve centimeter-level relative positioning accuracy. A technique, referred to as Dynamic Base Real Time Kinematic (DRTK) positioning, is described in detail to estimate the carrier-phase ambiguity to ultimately provide a relative position vector estimate between GPS antennas. DRTK is capable of providing relative positioning with L1, L2, and L5 frequencies standalone or in combination with one another. Performance improves with an increasing number of satellites in view and number of frequencies tracked per satellite. In this thesis, DRTK is aided by including an a priori baseline magnitude between antennas in a fixed attitude-baseline configuration on a single vehicle as a constraint with a technique referred to as Fixed Attitude-baseline DRTK (FAD). The RPV and relative integer ambiguities between these two fixed antennas, referred to as the base and auxiliary antenna, are computed and used to derive additional measurements between the base antenna and a rover antenna on a separate vehicle via vector addition (FAD+DRTK). This approach improves the availability of the solution by reducing the time-to-first-fix (TTFF) by one half when compared against DRTK with two receivers. A comparative study of FAD+DRTK and the conventional DRTK algorithm is presented when using low-cost single-frequency receivers.