analysis and simulation of slotted aloha-based rfid anti...

Abstract— Automatic Identification technology is a kind of

methods about automatically identifying objects without human

involvement. RFID reader can collect data from tags that attached to

objects and store the data to the computer as inputs. With the help of

computer system, highly automated information or data acquisition

process can be achieved. Automatic Identification technology is

developed rapidly and globally in recent decades. Using various

media as the information carrier forms different automatic

identification technology types, such as barcodes technology,

biometrics technology, magnetic stripes technology, Radio

Frequency Identification (RFID), Optical Character Recognition

(OCR), and voice recognition, etc. Radio Frequency Identification

(RFID) is a technology that uses radio waves for Automatic

Identification that was developed in 1980’s. RFID system consists

of two parts: RFID Tags that attached to the objects and RFID

Readers that can read information from tags. A RFID tag includes an

integrated circuit that contains information about the object and an

antenna to receive signals from RFID Readers and transmit

information to RFID Readers. This paper is to evaluate and analyze

the performance of slotted Aloha based anti-collision protocols and

simulation of Slotted Aloha Anti-Collision Protocol under normal

and interfering environments. The Simulation of the Slotted Aloha

protocol will be designed under the environment of Matlab.

Index Terms—Types of Aloha Protocol, Aloha, pure Aloha,

slotted Aloha.

I. INTRODUCTION

Frequency Identification (RFID) networks use radio

signal broadcast to automatically identify items with attached

RFID tags. A tag consists of a microchip that stores a unique

identifier and an antenna. The tag’s antenna is attached to the

chip and can transmit a unique tag identifier to a reader (also

called interrogator). The reader is capable of learning the set

of tags within its interrogation range.[1]

RFID tags can be classified into two types: Active RFID

tags and Passive RFID tags. Active tags contain batteries,

while passive tags need external power to provoke signal

transmission instead. The maximum working range of

passive tags is 3 meters. Active tags include battery assisted

passive tags, or called semi passive tags, with the working

range from 100 meters to 1000 meters respectively.

Salah Mohmad Aboghsesa, Tarek Mosbah Abdala, Nasarudin Daud , are with Department of Networking, Faculty of Creative Media and

Innovative Technology, Infrastructure University Kuala Lumpur (IUKL)

Kajang, Selangor, Malaysia, Email id:[email protected], [email protected], [email protected]

In RFID system, when more than one tag send signal to one

Reader simultaneously, the signals will be interfered with

each other, as Figure shows. Reader can receive signal from

Tag1 correctly during period t1. At period t3, Tag2 and Tag3

send signals to Reader while collision occurs at period t2.

Under this situation, the Reader cannot recognize the correct

signal either from Tag2 or Tag3, and this is called incomplete

collision. Period t4 shows the complete collision between

Tag2 and Tag3.

Collisions caused by conflicting communication signals will

influence the system efficiency and the data transmission

rate. Multi-tag system must employ an anti-collision

algorithm to avoid these collisions the most significant

algorithm used to solve the collision is Aloha algorithms.

II. ALOHA

ALOHA is a medium access protocol that was originally

designed for ground based radio broadcasting however it is

applicable to any system in which uncoordinated users are

competing for the use of a shared channel. Pure ALOHA and

slotted ALOHA are the two versions of ALOHA.

A. Pure ALOHA

Pure ALOHA uses a very simple idea that is to let users

transmit whenever they have data to send. Pure ALOHA is

featured with the feedback property that enables it to listen to

the channel and finds out whether the frame was destroyed.

Feedback is immediate in LANs but there is a delay of 270

msec in the satellite transmission [2]. It requires

acknowledgment if listening to the channel is not possible

due to some reason. It can provide a channel utilization of 18

percent that is not appealing but it gives the advantage of

transmitting any time.

B. Slotted ALOHA

Slotted ALOHA divides time into discrete intervals and

each interval corresponds to a frame of data. It requires users

to agree on slot boundaries. It does not allow a system to

transmit any time. Instead the system has to wait for the

Analysis and Simulation of Slotted Aloha-Based RFID

Anti-Collision Protocol

Salah Mohmad Aboghsesa, Tarek Mosbah Abdala, Nasarudin Daud

Figure 1: Pure ALOHA

2015 International Conference on Network security & Computer Science (ICNSCS-15) Feb. 8-9, 2015 Kuala Lumpur (Malaysia)

http://dx.doi.org/10.15242/IAE.IAE0215013 13

beginning if the next slot.

C. Slotted Aloha VS Pure Aloha

Slotted ALOHA is a refinement over the pure ALOHA.

The Slotted ALOHA requires that time be segmented into

slots of a fixed length exactly equal to the packet

transmission time. Every packet transmitted must fit into one

of these slots by beginning and ending in precise

synchronization with the slot segments. A packet arriving to

be transmitted at any given station must be delayed until the

beginning of the next slot. In contrast, for pure ALOHA, a

packet transmission can begin at any time.[4]

This diagram shows above the vulnerable period for

transmitted packets. In the case of slotted ALOHA, with

packets synchronized to slots, it is clear that the vulnerable

period is reduced to T seconds since only packets transmitted

in the same slot with the reference packet can interfere with

it.. The figure also shows the vulnerable period of pure

ALOHA, which is 2T.[4,5]

III. PROBLEM STATEMENT

There are some common problems with RFID which are

the reader collision and tag collision. Reader collision occurs

when the signals from two or more readers overlap. The tag is

unable to respond to simultaneous queries. Systems must be

carefully set up to avoid this problem.

Collisions bring extra delay, a waste of bandwidth, and

extra energy consumption to the interrogation process of

RFID.

IV. OBJECTIVES

The objectives of this project are:

To evaluate and analyze the performance of slotted

Aloha based anti-collision protocols.

Using simulation of Slotted Aloha Anti-Collision

Protocol under normal and interfering

environments. The Simulation of the Slotted Aloha

protocol will be designed under the environment of

MATLAB.

V. SYSTEM REQUIREMENT

In this paper we use MATLAB to evaluate and analyze the

performance of slotted Aloha based anti-collision protocols,

Microsoft Office 2010, Win 8 (64-bit version). 64-bit version

of MATLAB is the right choice for most situations, because it

can access the larger amounts of memory. However, we use

MATLAB software to make simulation on how to reduce the

collision.

VI. SIMULATION FLOW CHART

An overview of the simulator created using MATLAB to

calculate the time required to identify RFID tags with the

Frame Slotted Aloha protocol when interference is present.

Tags will pick a slot randomly and respond to the reader’s

query. More than one tag responding using the same slot will

result in a collision at the RFID reader end. Collided tags

need to be read again until the total number of tags is

identified. Each anti-collided tag interference is compared

with the user-entered probability of interference, and the tags

are taken as successfully read if the anti-collided tag

interference is greater than the user-entered probability of

interference. If not, those anti-collided tags need to be read

again. The simulator is run until the total number of RFID

tags is identified. Figure 4.1 below displays the flow chart of

the proposed simulator.

Figure 2: Slotted ALOHA

Figure 3: vulnerable period for transmitted packets.

Figure 4: Flow chart of simulation



VII. TESTING AND RESULT

The submitting author is responsible for obtaining

agreement of all coauthors and any consent required from

sponsors before submitting a paper. It is the obligation of the

authors to cite relevant prior work.

Authors of rejected papers may revise and resubmit them

to the journal again.

A. Test 1

In this test the probability of interference = .10 and

Number of RFID tags = 100 tags as shown in the figure

below.

B. Test 2



below.

C. Test 3



below.

VIII. ANALYSIS OF THE SIMULATION RESULTS

The table below showing the analysis result for the tests

that has been done.

As result, the table 1 shows that when probability of

interference increases, the time required reading all the tags

increases as well. Here, the total time required to read all the

tags is in addition to the time wasted because of tag collision

and interference. This is because, If we have more than one

tag is activated within the reading volume at a given time, the

tag signals will interfere with each other, giving an

ambiguous message to the reader. Depending on the

modulation method used in the tags, this mutual interference

has a variable effect on whether a valid reading of any tag in

the field will take place. Even in systems which utilize

Figure 6: Test 2

Figure 5: Test 1

Figure 6: Test 3

probability

of

interference

Number

of Tags

time

required

to read all

the Tags

(ms)

Highest

Collided

Tags

Slot with

Highest

Collided

Tags

0.1 100 283 61 81

0.5 100 487 57 194,169

0.9 100 2525 64 906

Table 1: Tests Results



"anti-collision" methods, multiple tags in the field will

increase the amount of time necessary for completed data

transactions of all the tags.

IX. CONCLUSION

The main issue in RFID system is a tag collision. There

may be more than one tag in reader working range. When

reader queried tags simultaneously it will create a tag

collision paradigm. That causes the loss of information in a

sophisticated identification system.

This thesis analyzes the performance of the Slotted Aloha

protocol when the interference for tag detection is not

present. Furthermore, it analyzes the performance of the

Slotted Aloha protocol when there is interference for tag

detection. Both simulations are capable of calculating the

time required to identify tags.

X. FUTURE ENHANCEMENT

In this simulation, it was assumed that there was a constant

value for interference that enters by the user throughout the

tag identification process. In the future, a model could be

created to analyze the performance of the Slotted Aloha

protocol when the interference changes dynamically during

the tag identification process for more accurate results.

REFERENCES

[1] de Paula, T. C. M., Lagana, K., & Gonzalez-Ramirez, L. (1996).

Mexican Americans. In J. G. Lipson, S. L Dibble, & P. A. Minarik (Eds.), A packet guide (pp. 203-221). San Francisco: USCF Nursing

Press.

[2] Kavanagh, K., Absalom, K., Beil, W., & Schliessmann, L. (1999). Connectin to the network using RFID: A Lakota example. Advances in

Nursing Science,21, 9-31. Retrieved March 26, 2001 from

ProQuest/Nursing Journals database. http://dx.doi.org/10.1097/00012272-199903000-00005

[3] Ulrich, T. (1997, September 22). Linking to the system. Time, 150,

30-33. Retrieved March 1, 2001 from InfoTrac/Expanded Academic ASAP database.

[4] Padilla, H. (2000, June 6).technique for human interface (Minneapolis,

MN), p. 1B. Retrieved February 28, 2001 from Lexis-Nexis Universe/General News database.

[5] Fredrickson, M. (2000).The magic of the RFIDs. Miami, FL: Annual

Meeting of the Speech Communication Association.

[6] Crow, G. K. (1988). Anus. (Doctoral dissertation, University of Utah,

1988). Abstract retrieved March 19, 2001 from CINAHL database.



http://dx.doi.org/10.1097/00012272-199903000-00005

http://dx.doi.org/10.1097/00012272-199903000-00005

http://dx.doi.org/10.1097/00012272-199903000-00005

http://dx.doi.org/10.1097/00012272-199903000-00005

http://dx.doi.org/10.1097/00012272-199903000-00005

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