written by justin on December 11th, 2007 @ 12:34 PM

Project Overview

The goal of this project is to create a localized positioning system (LPS) to determine the position of any object that is retrofitted with a XBee. This can be done through calculation of probable locations based on wireless signal strengths of communicating XBees. These XBee chips send and receive radio signals. These radio signals can be used to send simple commands to the XBee chips (to changes settings), or to send packets containing messages. These packages not only carry the message but also important information like the strength of the radio signal calculated by the reciever. These signal strengths can be used to determine probable positions of an unknown XBee. Using knowledge about the expected signal strength within the broadcast range of several given XBees the location of an unknown XBee can be determined.


This technology can be used for several purposes including those that are related to security and education. One example of using the technology for security purposes would be the tracking of high dollar resources. In addition, to security, it can also be used for robotics. For instance, robots can use the system as a tranparent sensor that provides location informaiton to determine and track its position relative to the local coordinate system. No matter what the need for the system is, the purpose is clear: to provide accurate position information for tracking and localization.


The three major components of the LPS system are the broadcast nodes, the system's software, and the XBees being tracked by the system. The system can be made up of as little as three broadcast nodes and currently has no upper bound on the number of broadcast nodes. The broadcast nodes work exactly as they sound. They continually broadcast a message out that can be captured and used by the tracked XBees to identify the broadcast node, its position, and the signal strength between the tracked node and the broadcast node.

The tracked XBees can work in one of three ways based on how the system is being used to track or locate the retrofitted object. The first method is to have the XBee connected to a computer through a USB prototype board. In this situation, the XBee will redirect the messages captured from the broadcast nodes directly to the computer to determine the position of the XBee. This method will be used for tracking systems with onboard computers.

The second method tracks stand alone XBees by having the stand alone XBee redirect the messages sent out by the broadcasting nodes to a XBee connected to a computer system via a USB prototype board. The computer system can then determine the position of the tracked node. This method will be used for tracking systems that are too small to contain an onboard computer.

The third method of tracking XBees will have the tracked XBees attached to some type of microcontroller like a PSOC or XBC. This method can perform basic trilateration on board without interfacing with any computer. This method prevents the XBee from taking advantage of any noise reduction, probabilistic, or intelligent system tracking techniques and will not be implemented by the project team.

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