RFID anti-collision protocol based on the window methodology to reduce the energy consumption and the identification time regardless of the tag ID distribution

Laburpena

Radio Frequency Identification (RFID) is a technology that uses radio frequency signals to identify objects. This technology enables the communication between the main devices used in RFID, the reader and the tags. The tags are attached to the different objects to be uniquely identified, and the reader receives an identification code (ID) stored on every tag. This produces great advances in applications such as manufacturing, shipping, and distribution environments. Using this technology for tracing or locating objects in the supply chain increases its efficiency and reduces the number of errors. The tags share a communication channel. Therefore, if several tags try to send information at the same time, the reader will be unable to distinguish these signals. This is called the tag collision problem. The consequences of this increase the time needed for identification as well as the energy consumption of the system. To minimize tag collisions, RFID readers must use an anti-collision protocol. Different kinds of anti-collision protocols have been proposed in the recent literature. One of the most popular strategies to solve this problem are the query tree based protocols, where the current response of each tag only depends on the current reader command (the query) but not on the past history of the reader’s queries. Under these types of protocols, the window methodology was proposed to decrease the number of bits transmitted by the tags, which also decreases the energy consumed by the RFID system. This methodology, however, assumes the ability of the reader to differentiate the query from the window size in the reader command. The first contribution proposed in this thesis is a protocol that is able to locate the bit string representing the window size in the received command by standardizing the number of bits used for that purpose, called the Standardized Query window Tree (SQwT) protocol. Apart from solving this issue, this protocol manages to decrease the number of bits transmitted by the reader and therefore the total number of bits transmitted in the identification process with respect to the windowed protocols. The adoption of tag IDs with the Electronic Product Code (EPC) standard provides an improvement of RFID, allowing it to access global networks. The EPC provides every tag with a unique ID that details the company, the type of product, the type of transport and a serial number. This organization causes tags stored in the same area to share some of their ID fields, such as the company or the type of product. Usually, tree based protocols have been successfully tested on tag populations with randomly generated IDs that possess a uniform distribution of all the IDs. That, however, is not the case when the EPC standard is used since the reader may face not only uniform, but also non-uniform distributions. The behaviour of tree based protocols under non-uniform distributions is severely affected, decreasing their performance. The second proposal in this thesis is a novel anti-collision protocol called the Flexible Query window Tree (FQwT) protocol, that is proposed with the aim of estimating the tag ID distribution, taking into consideration the partial tags’ responses of the window methodology to decrease the time needed to identify all the tags in the interrogation area with low energy consumption regardless of the type of tag ID distribution.