Radio Frequency IDentification (RFID) systems are becoming more and more popular in the field of ubiquitous computing, in particular for objects identification. An RFID system is composed by one or more readers and a number of tags. One of the main issues in an RFID network is the fast and reliable identification of all tags in the reader range. The reader issues some queries, and tags properly answer. Then, the reader must identify the tags from such answers. This is crucial for most applications. Since the transmission medium is shared, the typical problem to be faced is a MAC-like one, i.e. to avoid or limit the number of tags transmission collisions. We propose a protocol which, under some assumptions about transmission techniques, always achieves a 100 perfomance. It is based on a proper recursive splitting of the concurrent tags sets, until all tags have been identified. The other approaches present in literature have performances of about 42 in the average at most. The counterpart is a more sophisticated hardware to be deployed in the manufacture of low cost tags.
In binary search protocols, @cite_7 @cite_25 , the reader performs identification by recursively splitting the set of answering tags. Each tag has a counter initially set to zero. Only tags with counter set to zero answer the reader's queries. After each tag transmission, the reader notifies the outcome of the query: collision, identification, or no-answer. When tag collision occurs, each tag with counter set to zero, adds a random binary number to its counter. The other tags increase by one their counters. In such a way, the set of answering tags is randomly split into two subsets. After a no-collision transmission, all tags decrease their counters by one.
@cite_25 @cite_7
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This paper proposes a modification to the existing anticollision protocol put forth in version 1.0 protocol specification for 900MHz Class 0 RFID Tag. The version 1.0 specification uses a binary tree approach to singulate one RF tag ID at a time. The proposed change reduces the overall read time of a given number of RFID tags by resetting to the appropriate node, for every consecutive read cycle. The present standard resets to the root node of the binary tree for every read cycle. The multiaccessing of a broadcast communication channel by independent sources is considered. Previous accessing techniques suffer from long message delays, low throughput, and or congestion instabilities. A new class of high-speed, high-throughput, stable, multiaccessing algorithms is presented. Contentions resolving tree algorithms are introduced, and they are analyzed for specific probabilistic source models. It is shown that these algorithms are stable (in that all moments of delay exist) and are optimal in a certain sense. Furthermore, they have a maximum throughput of 0.430 packets slut and have good delay properties. It is also shown that, under heavy traffic, the optimally controlled tree algorithm adaptively changes to the conventional time-division multiple access protocol.