Anti-collision Algorithms for Multi-Tag RFID

RFID is one of automatic technology to identify and collect object data quickly through RF digital signals. RFID increases productivity and convenience. RFID is used for hundreds, if not thousands, of applications such as preventing theft of automobiles and merchandise; gaining entrance to buildings; automating parking. But one of the largest disadvantages in RFID system is its low tag (transponder) identification efficiency by tag collision. Collisions are divided into interrogator collisions and tag collisions. Interrogator collisions occur when neighbouring interrogators interrogate a tag simultaneously. Tag collision is the event that the interrogator (reader) cannot identify the data of tag when more than one tag occupies the same communication channel simultaneously. The reason is that whenever two or more users are transmitting on the shared channel simultaneously, a collision occurs and the data cannot be received correctly. This being the case, packets may have to be transmitted and retransmitted until eventually they are correctly received. As the most RFID systems use passive tags, frame sizes are limited in the framed slotted ALOHA algorithm. Especially, since low-functional passive tags can neither detect collisions nor figure out neighboring tags, a tag collision gives rise to the need for a tag anti-collision protocol that enables the recognition of tags with few collisions and also executes in realtime. Active RFID tags contain an on-board battery. They can communicate with interrogator in far distance. Active tags can provide anti-collision by using various combinations of some methods including time scope and frequency scope. When the number of tags is large, for the conventional RFID anti-collision algorithm, the number of slots required to read the tags increases exponentially as the number of tags does. Some methods can solve this problem with complex algorithm consuming long communication time. Based on the analysis above, a good tag collision arbitration protocol for RFID tags should have the following characteristics: First, a interrogator ought to identify all the tags inside its own reading range. Since the interrogator cannot estimate the number of tags precisely, the guarantee of recognizing all tags must be taken into consideration in the design of the tag hard system and anti-collision protocol. Second, a tag should be identified while consuming a small amount of resource, since the tag has low power. Thus, the tag anti-collision protocol must load the tag with the least possible communication time. This paper presents an improved dynamic framed slotted aloha algorithm (IDFSA) that may solve this problem by dividing frequency of tags that is grouping the tags in different Source: Radio Frequency Identification Fundamentals and Applications, Bringing Research to Practice, Book edited by: Cristina Turcu, ISBN 978-953-7619-73-2, pp. 278, February 2010, INTECH, Croatia, downloaded from SCIYO.COM