Radio Based User Presence

Abstract: While radio frequency identification tags (RFIDs) have been widely used for identifying objects (and some people), their primary use has been for access control, inventory, and other similar purposes. In this thesis we will use the detection of an RFID to indicate that a user is present in a given location.  This will be used to extend a Session Initiation Protocol (SIP) system with user presence. A typical HF RFID reader is able to read a tag from a range of 8-10 cm. In this application we wish to read tags from a range of 50 to 100 cm (the width of a doorway or narrow hallway). One of the challenges is how to increase the reading range while staying below the maximum RF power limits (for reasons of safety). Providing an RFID based presence indication can be used to automatically adjust the heating, ventilation, and air conditioning system of a room, etc. This thesis presents several different antennas which were analyzed and simulated using FEKO to obtain a suitable antenna for this target application. The thesis shows that fractal patterns are the best for the intended application based upon the results of simulations. These antennas were implemented and tested. The prototype establishes that such antennas are a suitable design and can be used with current RFID systems to achieve long ranges. The thesis also suggests some future enhancements to these antennas.