One of the major problems facing RFID systems today is that of tags not being read, resulting in reduced tag identification rates. This is more likely to happen as large number of tags is present in a small enclosure. We examine one of the causes for missed tags, namely coupling between adjacent tags. We present a theoretical explanation for the cause of coupling between tags and the mechanism by which it causes tags not to be identified. The concept of using a volatile state storage cell is examined. We study how state storage helps to eliminate missed tags, using the ISO 18000-6B protocol as an illustrative example. Experimental results using chips that have state storage capability are presented and we compare identification rates with and without using state storage. It is seen that when state storage is used, all tags are identified and is vastly superior to tag identification without state storage. For the first time, we present results showing how indispensable the concept of state storage is for passive RFID operation. The concept is readily extended to any protocol for passive RFID operation.
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