Localization system for UAV/UGV in urban environments.

摘要

An implementation of relative localization of wireless sensor nodes using a potential field method is presented in this work. The system is designed to assist in UAV/UGV navigation in urban environments like rooms and passageways of buildings. An unmanned vehicle will need to rely on ground-based sensors to help it navigate indoors, as GPS signals are severely attenuated and reception is intermittent. A sufficient number of sensors are first deployed throughout the terrain in a random fashion. They must then localize themselves to the environment, i.e. they must develop an internal frame of reference or co-ordinate system. A potential field method is used to achieve localization, where the potential (cost) is a function of the internode distances. Each node within the network is equipped with a Radio and Ultrasonic module and the distance between nodes is calculated by measuring the difference in time of flight of the RF and ultrasonic signals. The radio modules, based on the IEEE 802.15.4a standard, facilitate both internode communication and two-way ranging, making them ideal for use in an ad hoc network. A PC capable base station runs the localization algorithm in MATLAB thereby reducing the computational load on the nodes. Once localized, the nodes begin tracking the vehicle using a Kalman filter to estimate its trajectory. The data from the network has a limited update rate that is insufficient to track fast moving vehicles. The Kalman filter predicts the motion of the vehicle using its dynamic model and then corrects its trajectory when data becomes available. The hardware used in the sensor design was developed by the author, including electronic schematics, PCB design, component soldering and part of the supporting software.