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Real Time Location System using Passive UHF RFID

RFID technology is becoming more and more popular these days and on its top stands passive UHF RFID technology for it's economical as well as practical benefits. Even though this technology is intended for inventory, several attempts have been made by several vendors in creating a real-time location tracking system using passive RFID solutions.

The reason why passive UHF tags are so popular is its lower prize in compare with active tags and better results of Ultra High Frequency (865 MHz to 868 MHz for Europe) in compare with lower frequencies. From the economic point of view it is better to buy one expensive reader which can read millions of cheap tags than to buy one cheaper reader to read thousands of expensive tags.

Location tracking for passive RFID tags works much differently as those of the active variety. For active tags, the tag sends out a signal every predetermined interval. Then it is picked up by various antennas in range that record a time of arrival notification for each. These can be then converted into distance metrics using simple physics and spherical geometry calculates the location of the tag. Unfortunately passive tags and their antennas don't work this way. As a result all current location tracking models using passive RFID tags fall into one of two types. It is either a custom hardware design that doesn’t use typical off the shelf readers and tags, or it is a probabilistic model for calculating location. The former requires custom and typically expensive equipment to implement, the latter has its own pitfalls that must be overcome.

While other models require reference tags to have known locations this model does not. The tags merely need to be in at least two different antennas read zones when placed. In each antennas read zones a total of at least three tags must be present to ensure proper calibration of the model. Using tag filtering the tags placed as such can be classified as reference tags then not shown on output displays and tags that one wishes to track such as people wearing UHF RFID ID badges, will be the only tags shown.

Tags : passive UHF tags tracking system UHF RFID tags

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