Preventing Tag Collision in Radio Frequency Identification

Radio Frequency Identification (RFID) technology uses radio waves to identify the objects in a wireless manner. RFID system has many components. Among them most important are tags, readers and the antenna. Both tag and reader has many sub components for its operation. The object is recognized by the reader in terms of transmitting the signal to the tag [4]. RFID system has the following features such as long lifetime, less maintenance, no need of Line-of-Sight, contact-less technology, work in harsh environments and duplication of tags is difficult [10].

A tag collision occurs, if more than one tag attempts to communicate with a reader at the same time. The algorithm that is used to solve tag collision is termed as an anti-collision algorithm [4]. Earlier classification of algorithms based on multiple access techniques [7]. They are as follows: SDMA (Space Division Multiple Access), FDMA (Frequency Division Multiple Access), CDMA (Code Division Multiple Access) and TDMA (Time Division Multiple Access). TDMA comprises of largest group of anti-collision algorithms, those are divided into reader driven (reader talk first) and tag driven (tag talk first).

In Reader Talk First (RTF), tags remain quiet until it will be addressed by reader. In Tag Talk First (TTF), a tag advertises itself to the reader by transmitting its IDs. Among the two, TTF is very slow. RTF has two types such as ALOHA and Tree.

ALOHA have three types: Pure Aloha (PA), Slotted Aloha (SA) and Framed SA (FSA). FSA is divided into three types. They are: Basic FSA (BFSA), Dynamic FSA (DFSA) and Enhanced DFSA (EDFSA). Next major type is Tree based protocols. The types are Tree Splitting (TS), Query Tree (QT), Binary Search (BS) and Bitwise Arbitration (BTA) [7].

TS sp...

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...read 20 tags).

As shown in fig. 4, collision cycles get reduced but it could not be able to identify all the tags in case of re-entry, because of tag starvation problem (PRB requires 14 cycles to read 19 out of 20 tags).

VI. CONCLUSION

Re-entry problem involved in RFID tags are explained. The comprehensive survey and classification of RFID tag anti-collision algorithms have described. Also this paper analyses the effect of tag re-entry problem in the variants of binary tree algorithms. Due to the occurrence of collision, both ABS and SRB algorithms are inefficient to deal with tag re-entry problem and also it is difficult for PRB algorithm because of tag starvation. As a result ABS, SRB and PRB algorithms are critical to handle the tag re-entry problem. These problems may be resolve by means of including frame information in the tag after the identification process