Using Dynamic Slots Collision Tracking Tree Technique Towards An Efficient Tag
Anti-Collision Algorithm in RFID Systems
Chiu-Kuo Liang
Dept. of Computer Science and Information
Engineering, Chung Hua University
Hsinchu, Taiwan, R.O.C.
Email: ckliang@chu.edu.tw
Hsin-Mo Lin
Dept. of Computer Science and Information
Engineering, Chung Hua University
Hsinchu, Taiwan, R.O.C.
Email: e09902004@chu.edu.tw
Abstract—One of the research areas in RFID systems is a tag
anti-collision protocol; how to reduce identification time with a
given number of tags in the field of an RFID reader. There are
two types of tag anti-collision protocols for RFID systems: tree
based algorithms and slotted aloha based algorithms. Many
anti-collision algorithms have been proposed in recent years,
especially in tree based protocols. However, there still have
challenges on enhancing the system throughput and stability
due to the underlying technologies had faced different
limitation in system performance when network density is high.
Recently, a Bi-slotted Collision Tracking Tree Algorithm
(BSCTTA), which is a tree based approach, was proposed and
aiming to speedup tag identification in large scale RFID
systems. The main idea of BSCTTA is to track a collision bit in
order to reduce the prefix overhead and iteration overhead by
using time-divided response depending on whether the collided
bit is ‘0’ or ‘1’. In this paper, we proposed a dynamic slots
collision tracking tree algorithm, called the DSCTTA scheme,
to improve the performance of BSCTTA. Our proposed
DSCTTA method can reduce iteration overhead efficiently by
time-divided response depending on tracking consecutive
collision bits, and therefore can reduce prefix overhead further.
The simulation results show that our proposed technique
provides better performance than BSCTTA. It is shown that
the DSCTTA is effective in terms of increasing system
throughput and minimizing identification delay.
Keywords-Tag anti-collision, query tree, dynamic slots
collision tracking
I. INTRODUCTION
Radio Frequency IDentification (RFID) is an emerging
technology that guarantees to advance modern industrial
practices in object identification and tracking, asset
management, and inventory control [15]. Recently, several
identification systems such as barcodes and smart cards are
incorporated for automatic identification and data collection.
However, these systems have several limits in read rate,
visibility, and contact. RFID systems are a matter of grave
concern because they provide fast and reliable
communication without requiring physical sight or touching
between readers and tags.
One of the areas of research is the speed with which a
given number of tags in the field of RFID readers can be
identified. For fast tag identification, anti-collision protocols,
which reduce collisions and identify tags irrespective of
occurring collisions, are required [8], [9]. There are two
types of collisions: reader collisions and tag collisions.
Reader collisions indicate that when neighboring readers
inquire a tag concurrently, so the tag cannot respond its ID to
the inquiries of the readers. These collision problems can be
easily solved by detecting collisions and communicating
with other readers. Tag collisions occur when multi tags try
to respond to a reader simultaneously and cause the reader to
identify no tag. For low-cost passive RFID tags, there is
nothing to do except response to the inquiry of the reader.
Thus, tag anti-collision protocols are necessary for
improving the cognitive faculty of RFID systems.
In general, the tag anti-collision techniques can be
classified into two categories, aloha based and tree based
protocols. Aloha based approaches use time slot to reduce
collision probability, such as Framed-Slotted aloha algorithm
[1], [15], dynamic framed slotted aloha algorithm [2]. Tags
randomly select a particular slot in the time frame, load and
transmit its identification to the reader. Once the
transmission is collided, tags will repeatedly send its id in
next interval of time to make sure its id is successfully
recognized. Aloha based protocols can reduce the collision
probability. However, they have the tag starvation problem
that a particular tag may not be identified for a long time. For
the consideration of performance, when number of RFID tag
increased, the tag collision rate will be increased as well; this
may result a low tag recognition rate.
The tree based schemes use a data structure similar to a
binary search algorithm, such as query tree algorithm[3], tree
working algorithm [4], [5], collision tracking tree algorithm
[6], [7], [10], and bi-slotted collision tracking tree algorithm
(BSCTTA) [10]. An RFID reader consecutively
communicates with tags by sending prefix codes based on
the query tree data structure. Only tags in the reader’s
interrogation zone and of which ID match the prefix respond.
The reader can identify a tag if only one tag respond the
inquiry. Otherwise the tags responses will be collided if
multiple tags respond simultaneously.
Although tree based protocols deliver 100% guaranteed
read rates, but they have relatively long identification delay.
Recently, a bi-slotted collision tracking tree algorithm
(BSCTTA) [10] was proposed and aiming to reduce
transmission overhead by using bi-slotted response, in order
to speed up tag identification and to increase the overall read
rate and throughput in large-scale RFID systems.
2012 9th International Conference on Ubiquitous Intelligence and Computing and 9th International Conference on Autonomic
and Trusted Computing
978-0-7695-4843-2/12 $26.00 © 2012 IEEE
DOI 10.1109/UIC-ATC.2012.32
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