Autonomous following capability can improve operation efficiency when traveling from one location to another, providing the front lines of defense with fresh supplies, or mine clearing by reliably automatically formatting the spacing of vehicles. Many formations can be obtained, such as those suggested in Figure 1. In order for unmanned ground vehicles (UGVs) to possess autonomous following capabilities, the systems must have the ability to perform robust on-board relative navigation in many types of environments. This research explores methods for better integrating raw GPS carrier measurements and INS measurements from multiple vehicles to provide accurate relative motion between a lead and following vehicle.
Real Time Kinematic (RTK) or Carrier-Phase Differential GPS has been developed to provide very precise GPS position of a user relative to a fixed reference antenna. The method utilizes the raw GPS carrier signal to compute the relative distance between the two receivers, as seen in Figure 2. Most RTK systems rely on a stationary base station and low communication delays between the user and base station. Therefore this research explores the performance capability of using the carrier measurements to provide accurate relative positioning between moving GPS receivers. The methods developed investigate the effect of the moving reference antenna, communication delays, and short GPS outages. Accuracy of the carrier measurements and IMU sensor fusion for relative positioning when common satellites are used is studied. Additionally, the RTK/IMU sensor fusion with a moving reference antenna for various scenarios (varying number of satellites, varying sensor qualities, varying models, etc) are quantified as a means of providing designers an estimate of navigation accuracy of a given system.
Vehicle Convoy Formations
Schematic of RTK System