International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 4, April 2012)
Effective Collision Avoidance Mechanism for RFID Tags
Garima Saraf1, Md.Zahid Alam2
1
M.Tech Scholar, 2Asst. Professor, EC dept. LNCT, Bhopal, RGPV University, Bhopal, India
1
[email protected]
[email protected]
2
Abstract— RFID is technologies which transfer data
between electronic tag and reader by radio frequency for the
purpose of database auditing. RFID systems are used for
automated identification. It is also called Automated Data
Collection technology. In this, binary tree anti-collision
protocol search all possible tags based on their unique
identification numbers. Once a tag has been completely
identified, it will be eliminated. For reset, we use unique
sequence of no.’s for provide synchronization between reader
and tags. The mode of operation is the reader inquiring and
tag answering. Implementation of anti collision protocol is
done by VHDL language using Xilinx software. The design
methodology and results are useful for designing and
implementing a practical RFID system
Keywords- RFID, Active RFID tag, Anti collision protocol,
VHDL, Xilinx software.
I. INTRODUCTION
Radio Frequency Identification (RFID) is a technology
by which radio frequency (RF) communication is used to
store and retrieve data through a RF compatible integrated
circuit. Radio Frequency Identification (RFID) is one of
automatic Identification method. It is used for tracking and
tagging system for various products chain management
systems. Object identification problem Identify multiple
objects at the same time reliably. It is a silicon chip-based
transponder that communicates via radio waves. At the
present RFID becomes a standard for various products
chain management systems. Due to the huge potential and
robustness, RFID systems are used in a variety of
applications to uniquely identify the physical objects.
Figure 1 shows the basic organization of RFID systems, it
contains reader, tag and host computer for networking. The
RFID technology uses radio waves as a medium of
communication and it has some similarity with bar code
technology which was once a popular technology in the
identification industry. In this paper work, anti-collision
algorithm improves the readability, identification speed and
low-cost of RFID systems.
Figure 1: RFID systems
II. BLOCK LEVEL DESCRIPTION
The RFID system is always made up of three main
components; the transponder, the interrogator and the data
management system. The transponder or tag represents the
actual data-carrying device of an RFID system. The power
required to activate the transponder is supplied to the
transponder through the coupling unit (contactless) of the
reader. The transponder communicates with the reader, thus
the reader can get the data stored in the transponder. If
there are many tags within the interrogation zone of the
reader, and they communicate with the reader at the same
time, the reader will not know which one it should
communicate with at first. The reader will get the wrong
information of the tags if it cannot tell the individual IDs of
the tag.
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International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 4, April 2012)
The tags identification problem is associated with how to
efficiently develop anti-collision protocol in RFID tags [4].
Reader-to-reader interference occurs when a reader
transmits a signal that interferes with the operation of
another reader, thus preventing the second reader from
communicating with tags in its interrogation zone. This
type of interference occurs when the signal transmitted by a
reader is of sufficient strength and received at a second
reader that the signal communication from tag to the
second reader. Interrogation zones will not be needed to
have an overlap for reader-to-reader interference to occur
[4].
Figure 2: Block Diagram for Transmitter
III. METHODOLOGY
A. Implementation of Anti-Collision Algorithm for
Modified Binary Tree Protocol
In binary tree algorithm, anti-collision protocol searches
all possible tags based on their unique identification
numbers. Once a tag has been completely identified, it will
be eliminated. Inside every anti-collision tag contain
pointer. Every time the tag is reset and the pointer points to
the highest bit of the tag’s ID. This ongoing of inquiring is
moves toward the lowest bit. During inquiring the reader
sends one inquiring bit at a time [7]. The tags whose
pointed bit is the same as the inquiring bit will back send
their next bits to the reader and the tags whose pointed bit
is not same will convert to the state of “standby” and will
not answer the remaining inquires in this round. This
process will be continuing until one tag has been killed and
then all the remaining tags are reset. When the reader
senses a non-collision answer it uses the next-step inquiring
bit. But if a collision is sensed it uses a ’0’ bit as next-step
of inquiring. Thus every cycle of inquire only one tag will
be identified when the pointer reaches to the lowest bit of
the tag’s ID [7]. Then the identified tag will be killed and
all the other tags that have already entered the state of
standby will be reset [1]. After k cycles of inquiring, the
IDs in the k tags will all be identified. The anti collision
algorithm is implement for modify binary tree protocol
circuit using VHDL language with the help of Xilinx
software A step by step implementation has been done in
this study in order to achieve the final implementation of
anti collision protocol circuit. Implementation is done in
four steps such as data group, header detector, serial to
parallel and parallel to serial. By using Isim simulator,
results are analyzed in the form of waveform.
Figure 3: Block Diagram for Receiver
A. RFID Tag
Tag/Transponder: - The tag holds the data. Device made
up of an electronic circuit battery and an integrated antenna
An RFID tag is a microchip combined with an antenna in a
compact package; its packaging allow the RFID tag to be
attached to an object to be tracked [4]. The tag's antenna
picks up signals from an RFID reader or scanner and then
returns the signal, usually with some additional data. The
reader collision indicates that reader’s requests inquiries to
one tag concurrently, so it is confusing for the tag to
identify the inquiries. The tag collisions indicate that the
tags respond to one reader’s inquiry simultaneously and
reader cannot identify any tag [4].In RFID systems,
simultaneous transmissions between readers and tags
produce collision when it operates on the same channel. To
understand this, we will use concepts of interrogation
region and interference region for RFID readers. The
interrogation region is the region around a reader where a
single tag can be successfully read in the absence of any
interference from another tag or reader. The interference
region is a similar region where the signal from the reader
reaches with sufficient intensity so that it interferes with a
tag response. Without any coordination between the reader
and the tags, the responses from tags to reader can collide
[4]. The RFID collision problems classified in tags
identification problem and reader collision problem.
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International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 4, April 2012)
Figure 4: Schematic of Binary Tree Algorithm
Figure 5: Flow chart for receiving End Algorithm
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International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 4, April 2012)
IV. SIMULATION RESULT
A. Simulation of Header Detector:In RFID system, when multiple tags are in the range of
the reader, reader sends a starting bit to inform all the tag
with the intention of the reader is going to execute. Some
tag backscatter the most significant binary bit of their ID
but some tag Id not match with starting bit and go to back
off mode and randomly reset after few seconds. Due to
randomly reset, synchronization problem occur. To solve
these problem, I implement unique sequence of binary
no.’s for provide synchronization between reader and tags.
This no. are called header. In the process of reader tag
identification, every time tag is reset and pointer points to
the highest bit of the tag’s ID. For reset, reader sends
header sequence which is detected by tags. When tags
detect unique sequences it will be wake up and
identification process is continue.
Fig 7: RTL View of Header Detector
Figure 6: Flow Chart for Receiving End Algorithm
Fig 9: Simulation Result of Header Detector
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International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, Volume 2, Issue 4, April 2012)
B. Simulation of data group:In this work, tag contains 64 bit sequences Id which
provide company name, product name, serial no. etc. Data
group consist four channels A, B, C, D. Each channel
contain 16 bit information, all information divided between
these channel to increase identification speed, accurate
information and suitable for buffer storage. Tag holds the
data up to 128 Kbyte. Data is stored in non volatile
memory. Data receive from tag serially and stored in buffer
parallel. To convert, serial data into parallel for buffer
storage; in tag identification process, starting bit of tag is
detected and shift to next bit using shift resistor then all
detected bit stored in buffer bit by bit from MSB to LSB.
Buffer contains EEPROM which provide read and write
capability.
V. CONCLUSION
It was expected 700 no. of RFID tags simultaneously
identified in one second and remove collision between
reader and tags. In this research work, reader detects
multiple tag collision and identifies 600 no. of RFID tags in
one second. It also provides synchronization between tag
and reader. After implementation, I stimulate the code by
using test bench. This work solves the collision problem,
enhance the speed of signal transmission, channel
utilization, reduce the time slot and make the system more
stable. Simulation and result show that power consumption
and transmission delay is less. I have achieved 86% result
in this research. In future we implement this technology
to avoid following: Physical identity like reading through
liquid or metals. Nylon conveyor belts and other RFs can
disrupt the tag transmissions.
REFERENCES
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[5 ] Landt ” History of RFID. IEEE Potentials”, Vol.24, No. 4, (Oct.Nov. 2005).
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[7 ] Puah WL. 2007” Anti-collision protocol of RFID tags 2007”
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Fig 8: RTL View of Data Group
Fig 10: Simulation Result of Data Group
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