Comparative performance analysis of anticollision protocols in RFID networks

Radio frequency identification (RFID) is an automatic recognition system that consists of a number of tags and readers. An RFID reader identifies objects by reading the data contained in the tags [1]. RFID can be used in various applications ranging from identifying objects to using memory within its own chip. Attaching tags to wild animals, for instance, makes it possible to track them. For such reasons, the RFID system has been spotlighted as the technology that can replace bar code systems. Tags can be classified into two types based on the existence of self-electric power: active tags andpassive tags. The active tags can transmit datawithout the aid of a reader because it has its own battery. They also have amore powerfulmemory thanpassive tags. On the other hand, it is possible for a passive tag to transmit onlywhena reader is involved since it does not support self-electric power. Passive tags have constraints in functionality, but they have distinct advantages over active tags. They are small enough to attach to an object easily, and they do not need to consider power consumption due to its dependency on the reader’s power. In this chapter, the focus of consideration is to the passive tags. An RFID reader sends out a signal supplying power for tags. The tag extracts energy from the electromagnetic field by charging its capacitor until it is able to operate.When it is charged, communication between the reader and the tag is possible, that is why passive tags can operate without their own battery. An RFID reader communicates with tags through radio frequency, which is performed in a different manner than the bar code system in which a reader identifies a bar code through the light. Due to these characteristics, the RFID has wider range of identification of tags where tags can be identified even when line of sight (LOS) is not obtained. Both RFID system and bar code system readers are able to identify one object at a time. In a bar code system, one should secure the LOS between a bar code and its reader. It is possible to identify tags as long as they are within the reader’s range, but the order of identification should be determined. There may be multiple tags a reader should identify. All that the tags should do is to respond with the data corresponding to the signal received from a reader. The communication between tags is impossible when passive tags cannot make a decision on whether the channel is busy or not. Since a medium is shared by tags, a collision occurs at the reader’s side when two or more tags get transmitted simultaneously [2]. Since collisions make collided signals be retransmitted, it increases delay for identifying tags and consumption of energy. Therefore, the arbitration mechanism is required. We call the protocol designed for avoiding collisions between a reader and tags an anticollision protocol. The anticollision protocol should have the following characteristics:. A reader should identify all the tags within its range.