Smartening the Environment using Wireless
Sensor Networks in a Developing Country
A Neighbour Discovery Approach for Cognitive
Radio Network Using Tower of Hanoi (ToH)
Sequence Based Channel Rendezvous
Md. Rafiqul Islam1, M.A.E. Shakib1, Md. Azizur Rahaman1, Md.
Obaidur Rahman1, and Al-Sakib Khan Pathan2
1Department
of Computer Science and Engineering,
Dhaka University of Engineering & Technology, Gazipur, Bangladesh
2Department of Computer Science,
International Islamic University Malaysia, Kuala Lumpur, Malaysia
Presented By: Al-Sakib Khan Pathan
Outline of This Presentation
•
•
•
•
•
Introduction
Problem Statement and Related Works
ToH based Channel Hopping and Rendezvous
Performance Evaluation
Conclusions and Future Works
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Introduction
• Cognitive Radio Network (CRN) is a relatively
new research area to improve spectral efficiency
of wireless communication.
• Nowadays, the concept of commercial CRN (i.e.,
existence of primary and secondary users in
licensed bands) is gaining popularity in wireless
communication research.
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Introduction (Ctnd.)
• In CRN, two types of users namely Primary User
(PU), the owner of licensed band; and
Secondary User (SU) (shown in Figure 1), of the
unlicensed ISM band coexist.
• At the absence of PUs in licensed bands,
opportunistic medium access by SUs in licensed
channels renders better bandwidth provisioning.
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Primary & Secondary Networks
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Overview and Objective
• In CRN, SUs search the channels dynamically
and use the obtainable channels to enhance
throughput and connectivity.
• If two neighbour SUs want to communicate, both
should operate on at least one available
common channel during a particular interval of
time. Hence, both SUs can discover each other,
exchange control information and negotiate for
further data communication using MAC protocols
like IEEE 802.11.
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Overview and Objective (Ctnd.)
• Since the SUs operate independently on
different channels based on availability (i.e.,
during the absence of PUs), channel
rendezvous seems to be the most challenging
issue in CRN.
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SU Channels
Secondary users (SUs) may operate on various channels freely, at any given time.
This figure shows that nodes a and
b, p and q, x and y; the pairs of
SUs
opportunistically
make
channel rendezvous on channel 1,
channel 2, and channel 4,
respectively, where no primary
user exists. Note that channel 3 is
occupied by the PU; hence, SUs
do not have any activity on that
channel.
Channel - 1
a
b
Channel - 2
p
q
Channel - 3
Channel - 4
Occupied by Primary User
x
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y
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Message Broadcasting
Procedure of message broadcasting using channel hopping.
First Phase
In this procedure, to find
neighbours in CRN, an SU
broadcasts a control message
(i.e., informing its presence)
first on one channel and nodes
those get that message
repeatedly broadcast the
same information over multiple
channels.
Second Phase
Channel - 1
Channel - 2
Channel - 3
Channel - 4
b
a
b
d
e
c
c
f
Third Phase
d
c
e
g
f
a
g
Effectiveness and Performance are questioned
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Common Control Channel (CCC)
In CCC approach,
one common
channel is selected
from the available
channel list and
used as rendezvous
channel.
Control Interval
CCC or
Rendezvous Channel
Channel - 2
Channel - 3
Channel - 4
a
b
c
Data Interval
d
Occupied by Primary User
c
d
a
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b
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Pseudo Random Hopping
Pseudo random hopping sequence for SU x and y; where channel
rendezvous occurs on a channel (Ch-2) after ten iterations.
The channel hopping sequence as presented here, each SU generates a
pseudo random sequence and switches/hops from one channel to another
by following that predefined hopping sequence.
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Tower of Hanoi (ToH)
• In Tower of Hanoi (ToH) (sometimes referred to
as the Tower of Brahma or the End of the World
Puzzle), different sized disks are initially placed
in a first tower (initial) and all the disks are
needed to be shifted to a third tower (target),
taking help of a second tower (intermediate).
• At each of the tower and during disk
movements, a large disk should be placed under
a smaller disk.
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Tower of Hanoi (ToH)
1
2
2
3
3
Tower 1
3
Tower 2
1
Tower 3
3
2
1
1
1
2
2
1
1
2
3
1
3
1
2
3
1
1
2
2
3
3
2
1
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Our Proposal
• We assume the disks of the ToH as the
available channels to the SUs of a CRN.
• The number of disks equals to the number of
available channels, denoted by n.
• Larger numbered channel is considered to be
the larger disk and a smaller numbered channel
is considered to be the smaller disk, and so on.
• Therefore, the disks’ movement sequence that
we get using ToH method will actually provide a
channel hopping sequence for the SUs.
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Our Proposal (Ctnd.)
• Let, n disks (channels) need to be moved from first tower
(initial) to third tower (target) with the help of second
tower.
• Start Condition for Generating Sequence:
– Transfer all the n disks from first tower to third tower.
– Move only one disk at a time and store the disk ID (identity) in a
sequence.
– A large disk may not rest on top of a smaller one.
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Our Proposal (Ctnd.)
• End Condition for Generating Sequence:
– Add and store the sequence of disk movement whenever one
disk needs to be moved from one tower to another tower.
– The largest disk can only go to an empty tower.
– Similarly, transfer all the n disks from first tower to third tower.
– All transfer sequence will complete within (2n-1) steps.
– Finally, derive the sequence when the largest disk is in the
bottom and smallest disk is on the top of third tower.
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Our Proposal (Ctnd.)
• Let us assume that n = 3, so the ToH hopping
sequence will form a cycle having a length of
seven (i.e., using (2n-1)). Based on the example
given, if a particular SU has three available
channels namely, 1, 2, and 3; then, ToH
provides the channel hopping sequence as 1-21-3-1-2-1 having a cycle length of seven.
• ToH based sequence.
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Channels and Length of Cycle
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Flaw of Pseudo Random Seq.
• Suppose, a secondary user x has four available channels (1, 2, 3,
and 4) and y has two available channels (2 and 5). So, channel 2 is
common between x and y. If x and y maintain the pseudo random
sequence of the figure, even after twelve iterations, no possibility of
channel rendezvous between SUs x and y occurs.
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ToH based Sequence
•
Let us consider the similar scenario and generate the proposed ToH
sequence as in this figure. The SU x has four available channels (1, 2, 3
and 4) and the ToH sequence is 1-2-1-3-1-2-1-4-1-2-1-3-1-2-1 with a cycle
length of fifteen. In contrast, y has two channels (2 and 5) with a ToH
sequence of 2-5-2 having a cycle length of three. Since, the cycle
replicates again and again, in ToH based method, channel rendezvous
between x and y occurs within six iterations.
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Flaw of Basic ToH Seq.
• Problem in the proposed ToH based hopping sequence for
x and y; where channel rendezvous does not occur on
channel (Ch-4).
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Channel Sequence Shifting
• Channel Sequence Shifting. In the adaptive module, if any node is not
able to make channel rendezvous for several iterations, it would
presume that the generated ToH sequence is not allowing it to make
channel rendezvous with other nodes. Therefore, considering the
original ToH sequence as an origin, it will make a 1-bit left-shift in its
channel sequence. However, even after 1-bit left-shift, if channel
rendezvous does not occur, then the node will make 1-bit right-shift in its
channel sequence from the origin.
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Performance Analysis
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Performance Analysis (Ctnd.)
• Comparison of number of iterations required for channel
rendezvous, (a.) No. of Channels for Receiver = 2
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Performance Analysis (Ctnd.)
• Comparison of number of iterations required for channel
rendezvous, (b.) No. of Channels for Receiver = 3
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Performance Analysis (Ctnd.)
• Comparison of number of iterations required for channel
rendezvous, (c.) No. of Channels for Receiver = 4
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Performance Analysis (Ctnd.)
• Comparison of success rates of channel rendezvous.
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Final Words and Future Works
• The proposed approach is a novel one that uses
Tower of Hanoi (ToH) principle to derive the
channel hopping sequence for the SUs.
• It provides less number of iterations for channel
rendezvous with a higher success rate than that
of the existing pseudo random based approach,
which could be the apparent best alternative.
• In future, we aim to extend the work toward a
complete medium access solution for Cognitive
Radio Network.
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THANK YOU
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Questions and Answers
Any query should be directed to
[email protected] , [email protected]
???
For More Information:
http://staff.iium.edu.my/sakib/
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