International Journal of Engineering Trends and Technology (IJETT) – Volume 8 Number 2- Feb 2014
Order Optimal Algorithm for Neighbour
Discovery Using Feedback for Wireless Networks
Devika Adithya Das, T.K Parani
Student, ME Communication Systems Engineering, Anna University
DSCE Coimbatore, INDIA
Assistant professor Dept of electronics and communication engineering
DSCE Coimbatore, India
Abstract- Communication in wireless sensor networks is through
nodes. High quality network needs efficient communication
between nodes. Here Order-Optimal Neighbor Discovery Using
Feedback protocol is proposed for neighbor discovery .This
protocol exploits the feedback from the receiving nodes. It has
mainly three algorithms:-Collision detection based algorithm for
neighbor discovery, Asynchronous Collision detection based
algorithm for neighbor discovery, Order optimal Neighbor
Discovery Without collision detection. These three algorithms are
used for neighbor discovery. These algorithms are compared
based on two aspects:-Number of collisions, Time required for
finding the neighbors. Order-Optimal Neighbor Discovery
without Collision Detection is considered to be the best algorithm
for the process of neighbor discovery.
given time with high probability with high probability. In
deterministic neighbour discovery, on the other hand, each
node transmits according to a predetermined transmission
schedule that allows it to discover all its neighbours by a
given time with probability one.[2]In distributed settings,
determinism often comes at the expense of increased running
time and, in the particular case of neighbour discovery,
typically requires unrealistic assumptions such as node
synchronization and a priori knowledge of the number of
neighbours.
C. Challenges in neighbor discovery
Neighbour discovery is the discovering of neighbours and
it is a nontrivial for several reasons:-
I. INTRODUCTION
A. Wireless Networks
1.
A wireless network is a computer network that uses a
wireless network connection. It uses radio waves just like cell
phones, televisions etc .The most important advantage of this
network is that it allows the costly procedure of introducing
cables to diminish.
2.
What differentiates wireless communication from
wired communication is the nature of the communication
channel. Motion of the transmitter and the receiver, the
environment, multipath propagation, and interference render
the channel model more complex.
4.
5.
B. Neighbor Discovery
Communication in wireless network is through the nodes.
Data’s are transmitted in the form of packets from one node to
another node. Usually upon deployment a node does not have
knowledge about its specific neighbours. A high quality
network means there must be an efficient packet transmission
between nodes without any delay. In order to make a wireless
network an efficient network, the neighbour nodes must be
discovered. Thus, neighbour discovery is the first important
step in wireless networks.[1]
Neighbour discovery algorithms can be classified
into two categories, viz. randomized or deterministic. In
randomized neighbour discovery, each node transmits at
randomly chosen times and discovers all its neighbours by a
ISSN: 2231-5381
3.
Neighbour discovery needs to cope with collisions.
Ideally, a neighbour discovery algorithm needs to
minimize the probability of collisions and, therefore,
the time to discover neighbours.
In many practical settings, nodes have no knowledge
of the number of neighbours, which makes coping
with collisions even harder.
When nodes do not have access to a global clock,
they need to operate asynchronously and still be able
to discover their neighbours efficiently.
In asynchronous systems, nodes can potentially start
neighbour discovery at different times and,
consequently, may miss each other’s transmissions.
Furthermore, when the number of neighbours is
unknown, nodes do not know when or how to
terminate the neighbour discovery process.
D. Advantages
Unlike existing approaches that assume a priori
knowledge of the number of neighbours or clock
synchronization among nodes, a neighbour discovery
algorithm is proposed:
1.
2.
3.
P1 do not require nodes to have a priori knowledge
of the number of neighbours;
P2 do not require synchronization among nodes;
P3 allow nodes to begin execution at different time
instants;
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International Journal of Engineering Trends and Technology (IJETT) – Volume 8 Number 2- Feb 2014
4.
P4 enable each node to detect when to terminate the
neighbour discovery process.
Here Order-Optimal Neighbor Discovery Using
Feedback protocol is proposed for neighbor discovery .This
protocol exploits the feedback from the receiving nodes. It has
mainly three algorithms:1.
2.
3.
Collision detection based algorithm for neighbor
discovery
Asynchronous Collision detection based algorithm
for neighbor discovery
Order optimal Neighbor Discovery Without collision
detection.
Here Order-Optimal neighbor discovery using feedback
protocol to discover neighbors. There are mainly three
algorithms used in this protocol.[3]
II. ALGORITHM 1: COLLISION DETECTION BASED
NEIGHBOUR DISCOVERY
Here, in this algorithm each slot is divided into two sub slots.
Upon successful reception of a DISCOVERY message in first
sub slot ,each receiving node transmits bit1 to the source of
the message in second sub slot ,thus causing collision at node i
. Collision detection allows node i to detect that the second
sub slot is not idle and the transmission in the first sub slot are
received by all other nodes .Upon doing so it drops out
neighbor discovery i.e., stops transmitting.
The remaining nodes (henceforth, called surviving
nodes) then increase their transmission probabilities in the
next slot. Allowing nodes that have been discovered to drop
out and requiring the surviving nodes to increase their
transmission probabilities yields a significant improvement
over another neighbour discovery algorithm.
Initialize the variables b=0, flag=0,
Nbrlist=empty
Proximity calculation: P=1/(n-b)
No
If (flag=0
&& P=1)
Transmit the bit 1 in
second slot.
Yes
Transmit (Discovery (i)) in first
slot
Fig. 1 Flow chart of Collision detection based neighbor discovery
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As shown in the Fig.1 for the first algorithm collision
detection based neighbor discovery , here “b” defines the
number of neighbours discovered by node i. Flag describes
weather / node i been discovered by other nodes.
The Nbrlist shows the list of neighbours of node i. nb depicts the number of surviving nodes out of which each
transmit with the probability P=1/(n-b).Thus the proximity
calculation is done. If flag=0 and proximity is equal to 1,then
the neighbor discovery message is transmitted in the first slot.
If no transmission of bit1 is done in the second slot.[4]
The neighbors are discovered here, but the drawback
is the number of collisions which are necessary for neighbor
discovery. Less number of collisions are obtained in the
second algorithm. The time to discover the neighbors are also
being calculated.
III. ALGORITHM 2: ASYNCHRONOUS COLLISION
DETECTION BASED NEIGHBOR DISCOVERY
Unlike the synchronous version, receiving nodes
transmit feedback in response to the unsuccessful
transmission. This algorithm allows a node to begin
transmission despite detecting a busy period. The algorithm
performance can be improved by suppressing each
transmission.
In asynchronous collision detection-based algorithm,
which is presented in Algorithm 2, each transmission is of
fixed duration Ʈ and is followed by a feedback period of σ
duration .Here assumption is made that a node in the receive
mode can always detect if the wireless channel is busy or idle.
Thus К= Ʈ+ σ.
As shown in the figure 2, the timeline for an
asynchronous collision detection-based algorithm consists of:
1)Unsuccessful Busy Periods, during which two or more
nodes transmit
concurrently;
2) Feedback Periods immediately following message
transmissions;
3) Idle Periods during which no transmissions occur; and
4) Successful Busy Periods during which exactly one
transmission occurs. [8]
As in the synchronous algorithm, the key idea is to allow each
node that has been discovered by its neighbours to drop out
and let the surviving nodes increase their transmission rate.
Two observations about the collision detection-based
algorithm:
1) Unlike the synchronous version, receiving nodes
transmit feedback in response to an
unsuccessful
transmission. The reason for this choice is as follows. As
shown in the figure during an unsuccessful busy period, a
message transmission may overlap with the feedback period
of another message. Hence, sensing energy during the
feedback period has to be taken as an indication of
unsuccessful transmission.
2) Algorithm allows a node to begin transmission, despite
detecting a busy period. The algorithm performance can be
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International Journal of Engineering Trends and Technology (IJETT) – Volume 8 Number 2- Feb 2014
improved by suppressing such transmissions. However,
despite allowing such an event to occur, our analysis shows
that the algorithm takes only twice as long to complete
neighbour discovery than its synchronous counterpart.[6]
Initialize the variables. B=0,
flag=0, Nbrlist=Empty
discovery. These algorithms are compared based on two
aspects:1. Number of collisions
2. Time required for finding the neighbors
Number of collisions: Number of collisions are an important
factor in determining neighbors .Even though collision helps
in neighbor discovery, it causes congestion in the network. As
a result the three algorithms i.e. Order-Optimal Neighbor
Discovery Without Collision Detection, Asynchronous
Collision detection based neighbor .The neighbor discovery is
done even when the nodes cannot detect collisions.
L=1/(2k(n-b))
Initialize the variables b=0,
flag=0,id=-1,Nbrlist=empty
Set the ALARM (Timeout,
Exp(1/L).
Yes
Calculate Pxmit= 2^[r-1]/n]
If (collision
==yes)
Discover the packets
no
Transmit bit “1”
no
If(flag=0
&& B(p)=1
If(Discove
ry.id==1)
Yes
Transmit the
Discovery message
If Flag=0
Yes
Transmit the Discovery
message.
no
No
Discover source ID
Yes
n
Dropout
Flag=1.
(Drop Out)
P=logn/n
Fig 2. Flow Chart of Asynchronous Collision Detection Based Neighbor
Discovery
Yes
IV. ALGORITHM 3: ORDER-OPTIMAL NEIGHBOR
DISCOVERY WITHOUT COLLISION DETECTION
Order-optimal neighbour Discovery is achieved,
when nodes cannot detect collisions. Algorithm 3 presents a
neighbour discovery algorithm that achieves this goal. Node
hears its ID during a round; it “drops out” of neighbour
discovery at the end of the round. The neighbor discovery is
done even when the nodes cannot detect collisions. Instead of
providing a single bit of feedback, each node now includes in
its discovery messages the ID of the most recently discovered
neighbor in addition to its own ID.If a receiving node hears its
ID during a round, it drops out of “neighbor discovery” at the
end of the round.
This algorithm compared to the other three
algorithms discovers the neighbors without collision, therefore
the congestion in the network arriving due to collisions can be
reduced. These three algorithms are used for neighbor
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Discover the
neighbors.
If(flag=1
&& P=1)
no
Transmit the Discovery message
Fig 3. Order-Optimal Neighbour Discovery Without Collision Detection
Instead of providing a single bit of feedback, each
node now includes in its discovery messages the ID of the
most recently discovered neighbor in addition to its own ID.If
a receiving node hears its ID during a round, it drops out of
“neighbor discovery” at the end of the round.[7]
Time required for finding the neighbors: Time required for
finding the neighbor nodes are another important factor in
discovering neighbors. The algorithm which takes the least
time in discovering the neighbors is the most efficient
algorithm among three.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 8 Number 2- Feb 2014
V. EVALUVATION AND RESULT
A. Collision Detection Based Neighbor Discovery
The above figure 4.8 depicts the collision detection based
neighbor discovery. This is the synchronous version. The X
axis represents the number of neighbor. The Y axis represents
the number of collision. The graph shows that when the
number of nodes discovered is 10,000 the number of
collisions will be 25,000.And when the number of neighbor
discovered reach 40,000 then the number of collisions will be
55,000.
Fig 5 Asynchronous Collision Detection Based Neighbor Discovery
C. Order-Optimal Neighbour Discovery Without Collision Detection
Fig 4. Collision Detection Based Neighbour Discovery
Thus can make the conclusion that as the number of
neighbors being discovered increases ,the number of collisions
also increases. These collisions are undesirable as it will lead
to the congestion of the network.
B. Asynchronous Collision Detection Based Neighbor Discovery
The graph given above in figure 5 represents
asynchronous collision detection based neighbor discovery.
Here, The X axis represents the number of neighbor. The Y
axis represents the number of collision. As shown in the
graph, when the number of neighbor nodes discovered reach
10,000 then the number of collisions reach 15,000.And as the
number of neighbors discovered reach 40,000 the number of
collisions reach 50,000.Comparing with the collision detection
based neighbor discovery, this method will be more good as
the number of collisions reduces .Therefore in this method
the probability for network congestion will also reduce
drastically.
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Fig 6 Order-Optimal Neighbour Discovery Without Collision Detection
The graph given above in fig 6 represents orderoptimal neighbour discovery without collision detection.
.Here, The X axis represents the number of neighbor. The Y
axis represents the number of collision. As shown in the
graph, when the number of nodes discovered is 1000,the
collision amount is 45000,but as the number of neighbors
discovered goes on increasing example when it reaches
5000,the collision number will get reduced to zero. Thus
giving zero probability for the network congestion.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 8 Number 2- Feb 2014
D. Time to Discover
As shown in fig 7, the three algorithms Collision
detection based neighbor discovery, Asynchronous Collision
detection based neighbor discovery and Order-Optimal
Neighbor Discovery without Collision Detection are being
compared, on the basis of time to discover the neighbors. The
X axis represents the number of neighbor. The Y-axis
represents the time in milliseconds. To discover 50,000
neighbor nodes, the first algorithm takes 40,000 ms.To
discover the same amount of nodes ,the second algorithm
takes about 35,000 milliseconds.
And finally the same amount of nodes is discovered
by the third algorithm in just 15,000milliseconds.Thus it
proves that, the third algorithm ie Order-Optimal Neighbor
Discovery Without Collision Detection discovers the
neighbors taking the very least time, proving it to be more
efficient than any of the other two.
Neighbor Discovery Without Collision Detection are being
compared, on the basis of number of collisions.
The X axis represents the number of neighbors. The
Y-axis represents the number of collisions. To discover the
35,000 nodes, the algorithm1 takes 50,000 collisions. To
discover 35,000 nodes the algorithm 2 takes . The third
algorithm ie Order-Optimal Neighbor Discovery without
Collision Detection takes the less number of collisions eg: for
discovering 35000 nodes it doesn’t even take 7000 collisions.
The number of collisions is inversely proportional to the
number of network congestion. The third algorithm takes the
least number of collisions.
As Order-Optimal Neighbor Discovery Without
Collision Detection takes the least amount of time and takes
the least number of collisions to discover the neighbor nodes,
it is considered to be the best algorithm for the process of
neighbor discovery.
VI. CONCLUSION
Here the presented efficient neighbour discovery
algorithms for wireless networks are being compared.These
neighbour discovery algorithms do not require estimates of
node density and allow asynchronous operation. Furthermore,
our algorithms allow nodes to begin execution at different
times and also allow nodes to detect termination. OrderOptimal Neighbor Discovery Without Collision Detection
takes the least amount of time and takes the least number of
collisions to discover the neighbor nodes, it is considered to
be the best algorithm for the process of neighbor discovery.
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Fig7 Time to Discover
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E. Number of Collisions
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Fig 8 Number of Collisions
Here in figure 4.12, the three algorithms Collision
detection based neighbor discovery Asynchronous Collision
detection based neighbor discovery and Order-Optimal
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