Delft University of Technology
Faculty Mechanical, Maritime and Materials Engineering
Transport Technology

V.J.A. Thönissen Positioning and Tracking Systems
Literature survey, Report 2007.TEL.7195, Transport Engineering and Logistics.

The AGV laboratory of the section Transportation Engineering and Logistics of the faculty Mechanical, Maritime and Materials Engineering (3mE) at Delft University of Technology is a facility for research on Automated Guided Vehicle models. Determination of position and orientation of AGVs is essential for the system. Tracking AGVs can be achieved by repeated positioning. Positioning and tracking require specific systems. This report aims to provide an overview on positioning and tracking systems and recommends possible systems for the AGV laboratory.

A positioning system is a physical layer of one or more of the following components: mobile device (MD), positioning device (PD) and positioning server. Positioning is the process of determining the position (coordinates) of an MD. A positioning system can be expanded to a functional locating system, capable of linking a position to a symbolic location, an abstract idea of where something is. Finally this can result in a Location Based Service (LBS), providing a service to an MD based on its location. Tracking is specific service. Physical positioning and physical tracking are the main interests of this research.

The determination of the position of an MD in a positioning system starts with the traveling of signals between MD and PD based on positioning technologies. A technology gives a specific character to the signal. Technologies in positioning systems can be: US signals travel at the speed of sound and most often time for a signal to travel between MD and PD is measured. RF signals propagate at the speed of light. Either the time of travel or the signal strength is detected. IR light traveling in one direction can be measured by the direction of arrival. Electromagnetic fields can be distinguished based on signal strength. Video images can be analyzed on patterns. All technologies suffer from certain drawbacks. Some positioning systems apply multiple
technologies to diminish these effects. Combining multiple technologies is called technology fusion.

Incoming signals are measured by means of a positioning algorithm. Positioning algorithms are: Based on these measurement, the position of an MD can be calculated. ToA is the time for a signal to travel between MD and PD. Combined with the known velocity of the signal, the distance between the MD and the PD can be calculated. SS decreases over distance. Distance between MD and PD is calculated based on a function that represents the relation between the decrease of the SS and distance. AoA is the direction of an incoming signal. Based on the AoA of multiple receivers of which the positions are known, the position of an MD can be calculated. Scene analysis and proximity are locating algorithms recognizing patterns and presence respectively, and are sometimes combined with positioning algorithms. Applying multiple algorithms is known as algorithm fusion.

Positioning technologies and algorithms characterize a positioning system. Typically, these system properties are one of two opposing options. Criteria are possible requests of users for the system. Positioning systems typically communicate positioning data in Cartesian (x,y) or polar (r,θ) coordinates in 2D and Latitude-Longitude-Altitude, Cartesian (x,y,z) or polar (Φ,θ,r) coordinates in 3D. Adding the fourth dimension time (t) allows systems to track MDs.

The AGV system as it is implemented at the moment, sure has room for improvement. The Cricket Location-Support System can serve as an example to the AGV system, improving the system at many fronts. Main point of interest remains the required accuracy and precision level for the AGV system, which proves to be hard to match by other positioning and tracking systems. Further improvement or newer versions of the Cricket system might result in an attractive positioning and tracking system for the AGV laboratory.

Reports on Transport Engineering and Logistics (in Dutch)
Modified: 2007.11.24; , TU Delft / 3mE / TT / LT.