AN ENERGY-AWARE AND COVERAGE-PRESERVING

HIERARCHICAL ROUTING PROTOCOL FOR WIRELESS

SENSOR NETWORKS

Tzu-Shiang Lin

, Cheng-Long Chuang

, Chia-Pang Chen

, Chwan-Lu Tseng

En-Cheng Yang

Chi-Shan Yu

and Joe-Air Jiang

Department of Bio-Industrial Mechatronics Engineering, National Taiwan University, Taipei 106, Taiwan

Department of Electrical Engineering, National Taipei University of Technology, Taipei 106, Taiwan

Department of Entomology, National Taiwan University, Taipei 106, Taiwan

Keywords: Routing Algorithm, Sensing Coverage Problem, Wireless Sensor Networks (WSNs).

Abstract: Coverage-preserving and lifetime-prolonging are essential issues for wireless sensor networks (WSNs).

Providing full sensing coverage in a security-sensitive area is necessary for practical applications such as

security surveillances or military investigations. In order to prolong the duration of full sensing coverage,

we propose an Energy-aware and Coverage-presenting Hierarchical Routing (ECHR) protocol for randomly

deployed WSNs. The ECHR protocol accommodates energy-balancing and coverage-preserving while

selecting one cluster head for each round. The power consumption of radio transmission and residual energy

over the network are taken into account when determining an optimal route for a packet. The simulation

results show that ECHR prolongs the duration with full sensing coverage, which provides up to 85% extra

lifetime comparing with other protocols.

1 INTRODUCTION

Wireless sensor networks (WSNs) consist of a large

number of wireless sensor nodes. For the secure and

military applications (Stojmenović, 2005),

maintaining sensing coverage is extremely important,

because any coverage hole in a wireless sensor

network is not tolerable. Most of the previous

proposed routing protocols were designed to prolong

the lifetime of the network (Lindsey et al., 2002; Al-

Karaki et al., 2004). However, the sensor network

could become useless when the network fails to

maintain full coverage.

Usually, routing protocols were proposed to

prolong the lifetime of the network or enhance the

Quality of Service (QoS) (Mollanoori and Charkari,

2008). In order to decrease the energy consumption

of radio transmission, a Low-Energy Adaptive

Clustering Hierarchy (LEACH) routing protocol was

proposed by Heinzelman et al. (2002). Cluster heads

of the LEACH protocol provide data fusion in each

hop to reduce energy consumption, and then

transmit the sensing data to the base station (denotes

as BS). Therefore, energy consumption of sensor

node can be greatly reduced by preventing it from

transmitting the sensing data directly to the BS. In

addition, Tasi (2007) proposed a coverage-

preserving routing protocol, which was modified

from LEACH protocol and entitled it as LEACH-

Coverage-U protocol. The LEACH-Coverage-U

protocol calculates the overlap sensing areas of all

sensor nodes, and then uses this feature to select

cluster head. The simulation result shows that the

LEACH-Coverage-U protocol can prolong the

operational time when the sensing coverage is

greater than 50%. However, it produces large

amount of coverage holes during network operation.

Because of the random deployment, some

locations of nodes might be very close to each other

that causes overlapped sensing area. If these

overlapping nodes run out of energy earlier, the full

sensing coverage of the network can be maintained.

Hence, in this study, we present this study proposes

an Energy-aware and Coverage-preserving Hier-

archical Routing (referred as ECHR) protocol to

increase the duration of maintaining the full sensing

coverage in a WSN. The proposed ECHR protocol

Lin T., Chuang C., Chen C., Tseng C., Yang E., Yu C. and Jiang J. (2009).

AN ENERGY-AWARE AND COVERAGE-PRESERVING HIERARCHICAL ROUTING PROTOCOL FOR WIRELESS SENSOR NETWORKS.

In Proceedings of the International Conference on Wireless Information Networks and Systems, pages 53-56

DOI: 10.5220/0002181700530056

 SciTePress

always chooses one of the overlapping nodes to be

the cluster head in each round. In addition, we

applied the energy-aware hierarchical routing

mechanism to find out an optimal route for the data

measured by each node. Comparing with the

previous protocols, the ECHR protocol can

effectively prolong the duration of maintaining the

full sensing coverage in a WSN.

The rest of the paper is organized as follows:

Section 2 illustrates the radio transmission model

and coverage model of sensor nodes. The ECHR

protocol is presented in Section 3. Simulation results

are demonstrated in Section 4. Finally, concluding

remarks are given in Section 5.

2 PRELIMINARIES

In this work, assume that there are n sensor nodes

(denoted as S

, S

, …, S

) randomly deployed in a L

× L sensing field and the sensing field has m points

of interest (abbreviated as POI). The definition of

POI (denoted as P

, P

, …, P

) and the related point

coverage problem can be referred to the reference

(Cardei and Wu, 2005). Some assumptions for the

network model are also made: 1) All sensor nodes

and BS are all stationary after deployment. 2) The

BS is located far away from the sensing area. 3)

Each node has power control ability which can be

adjusted according to the transmission distance.

2.1 Radio Transmission Model of

Sensor Node

The first order radio model, which is the same as

that used in LEACH-Coverage-U protocol, was

adopted in this study (Tasi, 2007). There two

parameters, E

elec

and ε

amp

, involved in the energy

consumption model. E

elec

, the energy dissipations

per bit by the transmitter or receiver circuits, is set to

50 nJ/bit. ε

amp

, the energy dissipations per bit by the

transmitter amplifier, is set to

0.1 nJ/bit/m

. The

energy consumption for transmitting/receiving k-bit

data message under a given distance d, modelled in

Tasi (2007), is formulated by:

(, ) ( )

()

Tx elec amp

Rx elec

Ekd kE d

Ek kE

(1)

where E

is the energy consumption for transmitting

data, E

denotes the energy dissipation by receiving

data, and α is the pass loss exponent. The pass loss

exponent α is set to 2 for the transmission from each

node, and α is set to 2.5 for the transmission from a

cluster head to BS.

In addition, when an intermediate node receives

n k-bit message data, the node consumes energy of k

× E

units to compress the data into a packet with μ

× (n × k) bits, where μ is the compression coefficient,

and E

, the energy consumption per bit by data

aggregation, is set to 5 nJ/bit.

2.2 Coverage Model of Sensor Node

Each sensor node has sensing range r

and location

, y

}, i

∈

[1, n]. The location of each POI is {x

, y

∈

[1, m]. Then, we denote a coverage set of a

sensor node S

by CS

. The set of POIs that are

covered by multiple CS

can be determined by the

following equation:

(...

... )

ii n

OCS CS CS

CS CS CS

−+

=∩ ∪∪

∪∪∪∪

(2)

where O

is the set of POIs that are covered by

multiple sensor nodes. In addition, we define the

coverage ratio C of the network as

12 1

...

CS CS CS CS

−

∪∪∪ ∪

(3)

If a node S

runs out of energy, CS

in equation (3)

will be an empty set.

3 THE PROPOSED ECHR

ROUTING PROTOCOL

In order to prolong the lifetime of the network with

full sensing coverage, a cluster head selection

mechanism based on energy-balancing and

coverage-preserving was developed and used in the

ECHR protocol. We also apply the energy-aware

hierarchy routing mechanism to determine an

optimal route for packets generated by each node.

The detail functions about these mechanisms will be

described in subsection 3.1 and 3.2. The flowchart of

the proposed ECHR protocol is shown in Figure 1.

3.1 Cluster Head Selection Mechanism

According to the radio model described in the

subsection 2.1, the transmission between a cluster

head and the BS could consume a great deal of

energy. In the ECHR protocol, there is only one

cluster head in each round. Therefore, the cluster

head selection mechanism is essential. The head-

WINSYS 2009 - International Conference on Wireless Information Networks and Systems

weight H

for selecting node S

as a cluster head is

defined as

()

⎞

⎛

=×

⎟

⎜

⎜⎟

⎝

⎠

(4)

where the RE

is defined as residual energy, and c is

weight adjustment exponent.

After calculating head-weight of each node, the

node with the maximum head-weight will be chosen

to be a cluster head in one round. Then, the cluster

head broadcasts a beacon message to other sensor

nodes in the network. According to the message

contained in the beacon message, each node can not

only acquire the information of the cluster head, but

also obtain the information of the neighboring nodes.

The beacon message contains information that

consists of ID, residual energy, and hop count. The

information is updated when the sensor nodes

receive messages from other nodes.

3.2 Energy-aware Hierarchy Routing

Mechanism

In order to reduce the power consumption of data

transmission, we adjust communication range of

each node. Thus, all sensing data of sensor nodes

will be transmitted by multi-hop mechanism. Each

node uses the hop count of received information in a

neighbor table. Thus, each sensor node knows which

nodes are closer to the cluster head, and these nodes

could be its parent node. However, a node S

might

have multiple parent nodes available for choosing.

Therefore, we calculate the parent node factor Ф

for

the parent node S

by:

(1 / ) ( )

kkk

dREΦ= ×

(5)

where the d

is the distance between the node S

and

the parent node S

. According to equation (5), each

node calculates the parent node factor according to

its parent nodes and values saved in the neighbor

table. After calculating the parent node factor, each

node starts to transmit sensing data to its parent node.

Figure 1: Flowchart of the proposed ECHR protocol.

4 SIMULATION RESULTS

In this section, the performance of the ECHR

protocol is compared with those of LEACH and

LEACH-Coverage-U via numerical simulation. The

simulation environment is a network with 100 nodes

randomly distributed in an area of 50 × 50 m

. This

monitoring area consists of 2500 POIs, and the BS is

located at (25, –50). The initial energy of all nodes is

assumed to be 1 joule, and the sensing range r

is set

to be 7.5 m. Furthermore, the compression

coefficient μ is set to 0.05, and the data packet size k

is set to 2000 bits. We set the weight adjustment

exponent c to 8.5 in equation (4) with experience

obtained in priori.

Figure 2 shows the number of alive sensor nodes

versus the simulation rounds. LEACH protocol and

LEACH-Coverage-U protocol lose the first node at

about the 700th round. On the other hand, the

proposed ECHR protocol is able to maintain all

sensor nodes surviving till the 1620th round. After

the first node of the ECHR protocol runs out of

energy, the number of the alive nodes falls rapidly. It

is because the proposed ECHR protocol is able to

equalize the energy consumption over the entire

network. Figure 3 shows the coverage ratio versus

the simulation rounds. The proposed ECHR protocol

maintains 100% coverage ratio until the 1680th

round, but the LEACH protocol and LEACH-

Coverage-U protocol lose full coverage ratio at the

900th and the 1000th round, respectively. In other

words, the proposed ECHR protocol provides about

85% extra duration with 100% sensing coverage

ratio comparing with LEACH and LEACH-

Coverage-U protocols.

AN ENERGY-AWARE AND COVERAGE-PRESERVING HIERARCHICAL ROUTING PROTOCOL FOR WIRELESS

SENSOR NETWORKS

Figure 2: Comparison of the alive nodes of the proposed

ECHR protocol with those of other protocols.

Figure 3: Comparison of the coverage ratio of the

proposed ECHR protocol with those of other protocols.

Examining Figures 2 and 3, it clearly indicates

that the coverage ratio of the network adopting the

ECHR protocol is still maintained at 100% before

the first node runs out of energy at the 1620th round.

At the 1680th round, there are in total of 46 nodes

that run out of their energy, and the coverage ratio of

the entire network starts to fall out of 100%. This

result shows that the ECHR protocol is able to

prolong the duration of 100% network coverage by

choosing overlapping nodes to relay sensing data in

the most rounds of the simulation.

5 CONCLUSIONS

In this paper, we propose an energy-aware and

coverage-presenting hierarchy routing protocol for

wireless sensor networks. The goal of this study is to

prolong the duration for maintaining full sensing

coverage. The main idea is to combine energy-

balancing and coverage-presenting mechanisms into

routing protocol. Simulation results show that the

proposed ECHR protocol is able to prolong the

duration of the network with 100% coverage ratio,

which provides up to 85% extra lifetime comparing

with other protocols. We will try to evaluate the

performance of the ECHR protocol with respect to

transmission delay, and add some factors into our

ECHR protocol based on other information in our

future work.

ACKNOWLEDGEMENTS

The authors are grateful for the financial support

from the President of National Taiwan University

under contract no. 97R0533-2. This work was also

supported in part by the National Science Council,

Taiwan, R.O.C., under for financially contracts no.:

NSC 95-2218-E-002-073, NSC 96-2218-E-002-015,

and NSC 97-2218-E-002-006. Finally, the authors

would also like to thank the Council of Agriculture

of the Executive Yuan, Taiwan, for their financial

supporting under contract no.: 97AS-9.1.1-FD-

Z1(3).

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