A very fast tags polling protocol for single and multiple readers RFID systems, and its applications

In this paper, we present a very fast and simple protocol for polling tags in an RFID system formed by one or more readers, and a multitude of tags. Actually, the protocol is time-optimal for single reader systems, while being very fast for multiple readers systems. The main idea of the protocol described in this paper, is to associate a short and unique number (called "nickname" in the following) to each tag in the reader's range, and by using such nicknames as the polling order. We first describe the single reader version of the protocol. For this version, the used nicknames are the integers 1,2,...,n if the set of tags to be polled is formed by n tags. They can be seen as the time slot in which a tag has to communicate with the reader. We also provide a procedure to assign a nickname for a new tag, as well as a way to delete a tag from the polling order, while keeping the above consecutivity property about nicknames. When polled, the tags transmit a proper (usually short) message. Polling protocols, sometime with little changes, sometime with no change, can be efficiently used for solving several practical problems related to the use of RFID systems. Some of the most prominent ones, and those considered in this paper, are the problems of exactly determine missing tags, the collection of information associated to the tags, the probabilistic determination of missing tags (useful for raising a warning), and the determination of the presence of cloned tags, again for raising a proper warning. We formally show that the protocol is time-optimal. Besides, the protocol is privacy preserving since tags ID's are never transmitted during the polling procedure. In the protocol version for large, multireader RFID systems, we take an approach completely different from that used so far for any multireader protocol. Up to now, in the proposed protocols for this and related problems, first readers are scheduled so that those with overlapping ranges never operate at the same time. Then, single reader protocol for each so scheduled reader are applied. Here, we schedule the tags instead of the readers so that tags whose transmission can be received by a common reader, never operate at the same time. Then, we show that our polling protocol for single reader systems can be effectively used along with such a tags scheduling strategy, in multireader systems. The time performance improvement of our protocol over the known ones for multireader systems is very large, going from two to seven times, as shown by a simulation experiment we set up, and whose results are also presented.