Positioning and Tracking Systems
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
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
- Ultrasonic Sound (US)
- Radio Frequency (RF)
- Infrared (IR)
- Video analysis
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.
- Time of Arrival (ToA)
- Signal Strength (SS)
- Angle of Arrival (AoA)
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.
- Absolute versus relative denotes the difference whether an MD is
positioned in a shared reference coordinate system or is positioned
relatively to known positions.
- Active versus passive systems are distinguished by the transmitter of
the signal. When the MD sends the signal to the PD, the system is called
active and when the MD receives the signal from the PD, the system is
- Real time versus offline systems are characterized by difference in time
when the position of an MD is calculated and released. The former does it
without any time delay, the latter stores data until another moment in time.
- 2D versus 3D indicates the capability of the system to provide two
dimensional positions or positions in three dimensions.
- Indoor and outdoor systems differ in reach and size of 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.
- Exactness of a system is quantified by accuracy (error range of the
measurements) and precision (the percentage of measurements reaching the
- The scale of the system is defined by the size of the system and the
number of MDs to be distinguished (within a certain time interval).
- Cost related to the system are time (to build), space (occupation) and
- Limitations of the system are closely related to the positioning
technology applied. Loss of Line-of-Sight (LOS) is a common limitation of
IR, US and Video technology. Coverage range is typically small for IR and
electromagnetism signals. Disturbing sources like light, magnetic fields and
walls can influence measurements of signals applying respectively IR,
electromagnetism and US/RF/IR.
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)
, TU Delft