Wireless Sensor Network, 2011, 3, 351-356
doi:10.4236/wsn.2011.311040 Published Online November 2011 (http://www.SciRP.org/journal/wsn)
Copyright © 2011 SciRes. WSN
Energy Efficient Path Determination in Wireless Sensor
Network Using BFS Approach
Shilpa Mahajan1, Jyoteesh Malhotra2
1CSE, ITM University, Gurgaon, India
2ECE, GNDU, Amritsar, India
E-mail: Shilpa@itmindia.edu, Jyoteesh@rediffmail.com
Received September 9, 2011; revised October 10, 2011; accepted Octo b er 20, 2011
The wireless sensor networks (WSN) are formed by a large number of sensor nodes working together to pro-
vide a specific duty. However, the low energy capacity assigned to each node prompts users to look at an
important design challenge such as lifetime maximization. Therefore, designing effective routing techniques
that conserve scarce energy resources is a critical issue in WSN. Though, the chain-based routing is one of
significant routing mechanisms but several common flaws, such as data propagation delay and redundant
transmission, are associated with it. In this paper, we will be proposing an energy efficient technique based
on graph theory that can be used to find out minimum path based on some defined conditions from a source
node to the destination node. Initially, a sensor area is divided into number of levels by a base station based
on signal strength. It is important to note that this technique will always found out minimum path and even
alternate path are also saved in case of node failure.
Keywords: Graph Theory, Breadth First Search, Energy Efficient, Cost, Shortest Path
1. Introduction
A wireless sensor network (WSN) is a specialized wire-
less network that is composed of a number of sensor
nodes deployed in a specified area for monitoring envi-
ronment conditions such as temperature, air pressure,
humidity, light, motion or vibration, and so on. The sen-
sor nodes are usually programmed to monitor or collect
data from surrounding environment and pass the infor-
mation to the base statio n for remote user access through
various communication technologies. Typically, a sensor
node is a small device that consists of four basic compo-
nents 1) sensing subsystem for data gathering from its
environment, 2) processing subsystem for data process-
ing and data storing, 3) wireless communication subsys-
tem for data transmission and 4) energy supply subsystem
which is a power source for the sensor node. However,
sensor nodes have small memory, slow processing speed,
and scarce energy supply. These limitations are typical
characteristics of sensor nodes which effects, sensor
networks life and th e quality . For that reason, the proto-
cols running on sensor networks must consume the re-
sources of the nodes efficiently in order to achieve a
longer network lifetime. There is an ongoing research on
power organization issues in order to reduce the power u-
tilization when th e nodes become idle[1,2]. When power
efficient communication is considered, it is important to
maximize the nodes lifetimes, reduce bandwidth require-
ments by using local collaboration among the nodes, and
tolerate node failures, besides delivering the data effi-
An efficient routing technique is required to design a
network in a way to efficiently utilize the energy of
nodes to prolong the lifetime of the network. Since com-
munication consume significant amount of battery power,
sensor nodes should spend as little energy as possible
when receiving and transmitting data [3-5]. Network life-
time can be increased by reducing bandwidth consump-
tion by using local collaboration among nodes and toler-
ate node failures [6].
The proposed is based on single hop level by level
data transmission from the base station to the destined
node by forming a chain. All the nodes will have copy of
routing table containing information related to their ad-
jacent nodes. The path will be selected using BFS ap-
proach of graph theory.
1.1. Background
The earliest and simple approach was direct transmission
in which each sensor node will sense & transmit its data
to BS individually. Since base station is located far away
from sensor nodes resulting higher transmission cost.
Because of this high cost transmission the energy of
nodes drain off faster and thus having short system life-
time. In order to solve the problem, clustering based pro-
tocols were propo sed where a cluster is a gro up of sensor
nodes, with a head node managing all other member
nodes. The heads are responsible for coordinating mem-
ber nodes, gathering data within the clusters, aggregatin g
data and forwarding the aggregated data to the base sta-
LEACH [7] is a cluster-based, distributed, autono-
mous protocol. The algorithm randomly chooses a por-
tion of the sensor nodes as cluster heads, and lets the
remaining sensor nodes choose their nearest heads to join.
The cluster member’s data is transmitted to the head,
where the data is aggregated and further forwarded to the
base station. The LEACH algorithm reduces the number
of nodes that directly communicate with the base station.
It also reduces the size of data being transmitted to the
base station. Thus, LEACH greatly saves communication
energy. Since the protocol randomly chooses cluster
heads in each round , the energy consumption is theoreti-
cally evenly distributed among all sensor nodes data ag-
gregation techniques in WSN. They are clustering based
[4], tree-based [8], and chain-based [9]. In this section,
we only review three chain-based routing protocols,
PEGASIS [9], COSEN [10], and Enhanced PEGASIS [9],
and point out their pros and cons.
PEGASIS is a basic chain-based routing protocol [9].
In which, all nodes in the sensing area are first organized
into a chain by using a greedy algorithm, and then take
turns to act as the chain leader. In data dissemination
phase, every node receives the sensing information from
its closest upstream neighbor, and then passes its aggre-
gated data toward the designated leader, via its down-
stream neighbor, and finally the base station.
Although the PEGASIS constructs a chain connecting
all nodes to balance network energy dissipation, there are
still some flaws with this scheme. 1) For a large sensing
field and real-time applications, the single long chain
may introduce an unacceptable data delay time. 2) Since
the chain leader is elected by taking turns, for some cases,
several sensor nodes might reversely transmit their ag-
gregated data to the designated leader, which is far away
from the BS than itself. This will result in redundant
transmission paths, and therefore seriously waste net-
work energy. 3) The single chain leader may become a
In contrast to PEGASIS, COSEN [10] is a two-tier hi-
erarchical chain-based routing scheme. In that scheme,
sensor nodes are geographically grouped into several low-
level chains. For each low-level chain, the sensor node
with the maximum residual energy is elected as the chain
C) Enhanced PEGASIS
In 2007, Jung et al. proposed a variation of PEGASIS
routing scheme, termed as Enhanced PEGASIS [11]. In
their method, the sensing area, centered at the BS, is cir-
cularized into several concentric cluster levels. For each
cluster level, based on the greedy algorithm of PEGASIS,
a node chain is constructed. In data transmission, the
common nodes also conduct a similar way as the PEGA-
SIS to transfer their sensing data to its chain leader.
Chain-Based Hierarchical Routing Protocol, named as
CHIRON [12], based on the Beam Star concept [9], the
main idea of CHIRON is to split the sensing field into a
number of smaller areas, so that it can create multiple
shorter chains to reduce the data transmission delay and
redundant path, and therefore effectively conserve the
node energy and prolong the network lifetime.
In PEDAP (Power Efficient and Data gathering and
Aggregation Protocol), Chain is formed based on mini-
mum spanning tree and minimum energy concept [13].
The basic idea of CCPAR i.e. Clustered Chain based
Power Aware Routing Scheme for Wireless Sensor Net-
works scheme is that the nodes within a cluster are con-
nected in a chain and each node receives from and tran-
smits to the closest neighbors in the chain [14].This tech-
nique provide greater reduction in energy consumption
and thus increases the life time.
2. Proposed Algorithm
2.1. Level Assignment
First, sensor network area says M*M will be divided in
to number of concentric circles defined as levels. Each
node in the sensor networks is assigned its own level
based on signal strength from the base station. The num-
bers of these levels depend on various parameters such as
density of the sensor network, the number of nodes or the
location of the base station as shown in Figure 1.
The nodes are numbered in various levels say a nodes
that fall in level 1 will have numbers like (1-1), (1-2),
(1-3), (1-4).Similarly the nodes that lie in level2 will be
numbered (2-1), (2-2), (2-3) and so on. I n order to ease the
Copyright © 2011 SciRes. WSN
Figure 1. Level assignment.
concept of numbering we can even assign ID to each node
like A, B, C, D etc.
2.2. Route Discovery Phase
Route discovery is based on query and reply cycles, and
route information is stored in all intermediate nodes
along the route in the form of route table entries. Since
nodes do not have any route information, the route dis-
covery process can be initiated by each node by sending
a route request packet, to find neighboring nodes those
are one hop away from it .A source node will maintain
routing table containing information shown in Figure 2.
Each node can get to know its neighborhood by using
local broadcasts, so-called HELLO message. Nodes n eigh -
bors are all the nodes that it can directly communicate
The HELLO messages will never be forwarded be-
cause they are broadcasted with TTL = 1. After a mes-
sage has been broadcasted, a node will wait for route re-
ply message. As soon as source node receives route reply
message from nodes, it will upda te its routing table entry
destination ID. Sequence number will keep account of
the fresh routes. Battery status will give information re-
garding energy levels of the nodes. Visit field will help
in tracing a route from a source point to a destination
node. We will use the TTL =1, in order to find neigh-
boring nodes who are one hope away. Only those nodes
who have there energy level greater than defines thresh-
old level will take part in data transfer phase.
2.3. Breadth First Search Approach:
In graph theory, breadth-first search (BFS) is a graph
search algorithm [15] that begins at the root node and
explores all the neighboring nodes. Then for each of those
nearest nodes, it explores their unexplored neig h bo r n o d es,
and so on, until it finds the goal. It has been proved by
induction that the breadth first search tree is a shortest
path tree starting from its root. Every vertex has a path to
the root, with path length equal to its level (just follow
the tree itself), and no path can sk ip a level so this really
is a shortest path.
ID Destination
ID Node_
Status Sequence
nos Battery
Status Visit TTL
Figure 2. Routing table.
This algorithm uses queue to store the nodes of each
level of the graph as th ey are visited .These stored nodes
are then treated one by one and their adjacent nodes are
visited .These stored nodes have been visited. This ter-
minating condition is reached when the queue is empty.
There are three states that are defined with respect to
current node status. The field Node-Status will keep ac-
count of the states of the nodes.
A node that has not been visited yet and waiting to be
processed , will be in ready state .In the beginning all
nodes will be in ready state .As soon as the node is added
on to queue ,it will be waiting state.
The node that has been processed i.e. whose neighbors
have been added on to queue will be in processed state.
Nodes that have been processed once will not be consid-
ered again. So the field visit in a table will keep account
of it. In the beginnings all node will have zero in visit fi eld
as soon as a node is visited the value get updated to 1.
2.3.1. Table Construction
In the beginning phase, a route discovery will be initiated,
all nodes will update their routing table keeping in all
details .At this time visit field will be 0.Since, the cost of
sensing is less as compare to cost of communication.
For example consider a tree of nodes as shown in Fig-
ure 3.
In the Beginning:
For Node A
Src IDDest IDN_StatusS nos Battery
Status Visit TTL
A B Ready 111(say) B (Say) 0 1
C Ready 112(say) B (Say) 0 1
D Ready 113(say) B (Say) 1 1
For Node B
Src IDDest IDN_StatusS nos Battery
Status Visit TTL
B E Ready 121(say) B (Say) 0 1
C Ready 112(say) B (Say) 0 1
A Ready 122(say) B (Say) 1 1
Figure 3. Tree structure.
Copyright © 2011 SciRes. WSN
All nodes will update their routing table accord ingly in
the initialization phase. After this, a route discovery phas e
will start from the farthest node say base station in wire-
less sensor network field. Queue will be maintained, the
staring node say A will be in processed state an d all other
like B,C,D are in waiting state.
Src ID Dest ID N_Status S nos Battery
Status Visit TTL
A B Waiting 111(say) B (Say) 1 1
C Waiting 112(say) B (Say) 1 1
D Waiting 113(say) B (Say) 1 1
Like wise when Node B will be processed from Queue
Src ID Dest ID N_Status S nos Battery
Status Visit TTL
B E Waiting 121(say) B (Say) 1 1
C Waiting 112(say) B (Say) 1 1
A Waiting 122(say) B (Say) 1 1
Once all the nodes have updated table de tails with sig-
nificant data. Breath first search algorithm will be cal-
led .Various steps for the algorithm is:
Algorithm BFS(G)
Step 1: Initialize all nodes to ready state (status =1)
[Here n can be defined as the nu m ber of no d es. Ini -
visit =0
For (i=1; I <= n; i++)
Visit[i] =0;
Step 2: Put the starting node in queue and change its
status to the waiting state (status =2)
[Initialize starting node say v and make visit[v] =1]*
[Add on to queue [v], initialize to pointers to keep track]
Of front and rear element of queue
Front=Rear=–1 [initially]*
Rear=front=0 [incremented]*
[Rear++, front++]*
Queue [Rear]= v
Step 3: Repeat step 4 and 5 until queue is empty
[Check while (front<=Rear)]*
Step 4: Remove the front node n of queue. Process n
and change the status of n to the processed state (status
[Deleting element from the queue]*
v = queue [front]
front++ //incrementing front by one
Step 5: Add to the rear of the queue all the neighbors
of n that are in ready state (status =1), and change their
status to the waiting state (status =2). [End of the step 3
[find out all the nodes adjacent to v]*
For (i=0; i<=n; i++)
Adj[v][i]==1 and visited[i]==0
Step 6: Exit
2.4. Implementation
1) All nodes have same and adequate amount initial
2) A node can trust each other and there is no mali-
cious intruder.
3) Each node or sink has ability to transmit message to
any other node and sink directly.
4) Each sensor node has radio power control; node can
tune the magnitude according to the transmission dis-
5) Each sensor node has location information.
6) Every sensor nodes are fixed after they were de-
7) WSNs wo u l d not be mainta ined by humans .
8) Wireless sensor nodes are deployed densely and
randomly in sensor field .
This concept can be explained by taking an example of
10 nodes and finding a path from a given node to a des-
tination node as shown in Figure 4.
We have considered a network of 10 nodes .The nodes
have been leveled based on the signal strength from the
base station .A base station is the furthest node .Each
Node has updated routing table keeping an account of
nodes that are one hop away from it.
So the adjacency list will be:
[]*: comments Figure 4. Nodes arrangement.
Copyright © 2011 SciRes. WSN
NODES Adjacent List
Once this list has been created, A BFS approach can
be used to find the minimum connected path/Spanning
tree from a furthest node to a destination node as in Fig-
ure 4 say (to find a path from A to I). While applying
this algorithm, we will also keep account of the origin
A: B
Origin: A
B: C, E
Origin: B, B
C: E,D,F
Origin: B,C,C
E: D,F
Origin: C,C
D: F,G,P
Origin: A,D,D
F: G,P,H
Origin: D,F,F
G: P,H,I
Origin: F,F,G
P: H,I
Origin: F,G
H: I
Origin: G
I: -
Origin: -
Considering nodes with their origin nodes;
Path selected will be
2.5. Simulation
A simulation of BFS has been done on mat lab 7.0 con-
sidering a random network of 10 nodes. A trusted path
distance has been calculated and is compared with
AODV hop by hop network of 10 nodes .A graph has
been plotted considering different ranges and corre-
sponding distances has been plotted. All the assumptions
discussed above have been kept in mind while perform-
ing a simulation.
Graph 1. Distance vs range
3. Conclusions
In this approach, nod es in the network are stationary and
in next round when a node has a data to send to some
other destined node, there is no need to create a routing
table again and again until nodes have energy greater
than threshold level. Only those nodes that are selected
will be active and other nodes that don’t take part will
remain in sleep mode. Nodes who have their energy less
than threshold will not particip ate and thus in those cases
the routing table has to be maintained again. This ap-
proach will always result in finding the shortest path
from a base station to a destined node. In future this
method can be in corporate with MAC layer issues. Also,
more comparisons study can be done with other proto-
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