We can identify the collision bit by bit if Manchester coding is used. This possibility is useful when there is not many tags in an interrogation area.
Weakness of Passive Tag:
Tag collisions is problematic as a tag has limited power and functionality. A passive tag can only transmit data by reflecting the reader transmitted electromagneticwaves, and hence, cannot detect nor communicate with the neighboring tags. The energy received by a tag is usually less than 100μW. Accordingly, CSMA-related methods are not practical anti-collision algorithms for the passive tags.
ISO 14443-3
Type A bit collision detection
Type B series of command sequence
ISO 15693
More detail about ISO, they are not just anti-collision protocols.
http://rfidwizards.com/index.php?option=com_content&task=view&id=242&Itemid=174
After review some anti-collision articles, I find out there are two main streams of anti-collision algorithm: ALOHA based and tree based. First one is probabilistic and the last one is deterministic.
After one weak research, I finished the first step in reviewing current papers about those proposed algorithms, and have better understanding the constrains existed in development process. I will concentrate on the most common scenario: passive tags with one reader sharing one channel, to consider the algorithm. Next step is brainstorming.
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