Extracting information from tag collisions

In this paper, we develop techniques to extract information from communication collisions involving passive UHF RFID tags. Our goal is to extract information that can enhance the performance of existing anti-collision protocols. Present RFID anti-collision protocols detect a collision at the medium access control (MAC) layer; however, the physical layer signal received during collisions is discarded. This signal contains valuable information, such as the number of tags communicating, that can be used in the anti-collision algorithms. Collecting and utilizing this currently discarded information would provide performance improvements to existing protocols and provide insights that can be used to guide the development of future protocols.We analyzed communication collisions from ISO 18000-6C compliant tags in their response to a Query command. Our techniques enabled us to reliably identify the exact number of tags in the collided slot for up to 4 tags communicating in that slot and the existence of at least 5 tags communicating in a slot with more than 4 tags communicating in that slot.