Detection and location of passive and semi-passive RFID tags in in-door environments

This presentation will review the development of Radio frequency identification (RFID) technology, which has received increasing research interest in recent years due to its huge potential in asset tracking and localization. The most promising feature of this technique is its ability to identify an RFID tagged object from a distance, which, unlike traditional bar-code techniques, does not require line of sight between the reader and tag. Clear applications have been identified for active, semi-passive and passive RFID tags, with battery-free tags being recognised to be particularly appropriate for very low cost situations. A challenge with such tags however is in ensuring highly reliable detection particularly in environments where in-door features lead to RF nulls. This, in turn affects location accuracy. In recent years, the problem of nulls has been overcome by using phased array antennas and distributed antenna system (DAS) approaches. For example, researchers have achieved wide area coverage by maximizing the link budget through space time array techniques, smart antennas and digital beam forming. In respect of DAS, excellent performance has been achieved by distributed transmitter and receiver signal control and signal processing, so that >99% reliability has been achieved for tag numbers in excess of 100 over areas of up to 20 m × 20 m. Research has additionally identified that by careful design, larger areas can be monitored using multiple cells where cell to cell interference can be used to enhance read reliability. Wireless antenna nodes can also be used to enhance read range. This paper will therefore review the current status of this rapidly developing field, and describe recent advances in location.