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.
All the protocols proposed so far exhibit an average performance (both in terms of messages and in terms of transmitted bits, two metrics strictly related to system efficiency) well below 50 , the best performing protocols, namely QT and TSA, perform around 40 @cite_6 @cite_27 . Such results are reported in the above papers, where the protocols have been proposed, and were substantially confirmed in a paper @cite_28 describing an extensive simulation experiment set up for assessing the average performance of several tag identification protocols.
@cite_28 @cite_27 @cite_6
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In this paper, we approach the problem of identifying a set of objects in an RFID network. We propose a modified version of Slotted Aloha protocol to reduce the number of transmission collisions. All tags select a slot to transmit their ID by generating a random number. If there is a collision in a slot, the reader broadcasts the next identification request only to tags which collided in that slot. Besides, we present an extensive comparative evaluation of collision resolution protocols for tag identification problem in RFID networks. After a quick survey of the best performing RFID tag identification protocols, both deterministic and probabilistic, we present the outcome of intensive simulation experiments set up to evaluate several metrics, such as the total delay of identification process and the bit complexity of reader and tags. The last metric is strictly related to energy constraints required by an RFID system. The experiments point out that our protocol outperform all the other protocols in most cases, and matches them in the others. This paper presents an efficient collision resolution protocol and its variations for the tag identification problem, where an electromagnetic reader attempts to obtain within is read range the unique ID number of each tag. The novelty of our main protocol is that each tag is memoryless , i.e., the current response of each tag only depends on the current query of the reader but not on the past history of the reader's queries. Moreover, the only computation required for each tag is to match its ID against the binary string in the query. Theoretical resulst in both time and communication complexities are derived to demonstrate the efficiency of our protocols.