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1st Int'l Conf. on Recent Advances in Information Technology | RAIT-2012 | ... lifetime of the wireless sensor network with respect to the parameters FND (First ...
1st Int’l Conf. on Recent Advances in Information Technology | RAIT-2012 |

Energy Efficient Cluster Head Selection in Wireless Sensor Network Anindita Ray

Debashis De

Department of Computer Science & Engineering BF-142, Sector 1, Salt Lake City, West Bengal University of Technology Kolkata 700064, West Bengal. [email protected]

Department of Computer Science & Engineering BF-142, Sector 1, Salt Lake City, West Bengal University of Technology Kolkata 700064, West Bengal. [email protected]

Abstract: This paper presents an improved version of LEACH protocol which aims to reduce energy consumption within the wireless sensor network and prolong the lifetime of the network. This paper improves LEACH protocol by improving the election strategy of the cluster-head nodes based on remaining energy of sensor nodes, distance from base station and the number of consecutive rounds in which a node has not been a cluster head. Also it considers the factor that whether the nodes remaining energy is sufficient enough to send the aggregate data to the base station or not. If the nodes remaining energy is not sufficient enough it cannot be selected as cluster head. Simulation results shows that the proposed protocol could better reduce energy consumption and prolong lifetime of the wireless sensor network with respect to the parameters FND (First Node Dies), HND (Half Node Dies) and LND (Last Node Dies). The proposed protocol is 41.7% better than LEACH with respect to FND, 31.6 % better than LEACH with respect to HND and 25.5% better than LEACH with respect to LND.

II. PROBLEM FORMULATION Low Energy Adaptive Clustering Hierarchy (LEACH) [2] is the first hierarchical cluster-based routing protocol for wireless sensor network which partitions the nodes into clusters, in each cluster a dedicated node with extra privileges called Cluster Head (CH) is responsible for creating and manipulating a TDMA schedule and sending aggregated data from nodes to the base station (BS) where these data is needed using CDMA. Remaining nodes are cluster members. In LEACH cluster-heads are stochastically selected. In order to select cluster-heads each node n determines a random number between 0 and 1. If the number is less than a threshold T(n), the node becomes a cluster-head for the current round. The threshold is set as follows:

T (n) =

Keywords: WSN, LEACH, PEGASIS, BEC, PECRP

I. Introduction Wireless sensor network [1] is composed of hundreds of sensor nodes involving in limited energy, efficient and low energy consuming routing protocol. One of the major challenges in WSNs is to ensure an extended lifetime to the sensor nodes. Many researchers have tried [2-17] to optimize this problem. This paper improves LEACH protocol[2] by improving the election strategy of the cluster-head nodes, considering residual energy, distance from base station , number of consecutive rounds in which a node has not been a cluster head and the factor that whether the nodes remaining energy is sufficient enough to send the aggregate data to the base station or not. If the nodes remaining energy is not sufficient enough it cannot be selected as cluster head. Simulation result shows that the proposed protocol has better performance than LEACH [2], the protocol referred in [3] and EECHS[17] .Section II describes Problem formulation, Section III lists related work, section IV describes proposed protocol, section V shows simulation results and analysis, and section VI concludes this paper.

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T (n) = 0

p

∀n ∈ G

 1 1 − p ×  r mod  p  ∀n ∉ G

(1)

with P as the cluster-head probability, r as the number of the current round and G as the set of nodes that have not been cluster-heads in the last 1/P rounds. This algorithm ensures that every node becomes a cluster-head exactly once within 1/P rounds. Although the randomization of electing cluster-head nodes can distribute the load among the network, it suffers from the following drawbacks•



LEACH randomly elects cluster-head and prone lead to the unbalanced energy level reserved in nodes and thus increase the total energy dissipated in network. The election of cluster-head nodes ignores the residual energy information about the nodes and this will easily result in the cluster head nodes disable.

1st Int’l Conf. on Recent Advances in Information Technology | RAIT-2012 |





It ignores the distance factor between the nodes and the base station. It assumes that every time a node becomes a cluster-head, it can communicate with Base station directly. This is incorrect, as cluster-heads located far from the base station spend more energy in transmitting data those located near to the base station. Here the number of consecutive rounds in which a node has not been a cluster head is not considered directly.

Since LEACH has many drawbacks, many researchers have tried to make this protocol performs better [3-17].

Einitial is the initial energy of node before transmission as in[10]. Variable i indicates the serial number of nodes. Distance factor D(i)= d iB/ d Farthest.

(6)

Where diB is the distance from node i to BS as follows: (7) d iB= √(X i-XBS)2+(Y i-YBS)2 and d Farthest is the distance of the farthest node from the BS as in [10].Here () is the location of the Base Station.

LEACH's[2] stochastic cluster head selection algorithm is extended in [3] by adjusting the threshold T(n) denoted in equation (1), relative to the nodes remaining energy as follows:

In third parameter (s div r) of equation (4), s is the number of consecutive rounds in which a node has not been a cluster head and r is the number of the current round. Here P, n and G in the equation (4) express the same meaning as in equation (1).

E residual (2) K opt )  1  E initial  1 − p ×  r mod p   Where E residual is the remaining energy of the node and E initial is the initial energy of the node before transmission.

Instead of considering these three important parameters, EECHS does not consider the factor that whether the nodes remaining energy is sufficient enough to send the aggregate data to the base station or not.

p

T (n) = (

K opt =

ε

N 2π

fs

M

(3)

ε mp d to2 BS

Where K opt is the optimal cluster head number, N is the total number of sensor nodes, M is the length of nodes distributing fields, dtoBS is the distance between the nodes and the Base Station as in[5].Although election strategy of cluster head nodes in[3] considers residual energy as a parameter, but it ignores the distance factor between the nodes and the base station. And the number of consecutive rounds in which a node has not been a cluster head is not considered directly. In EECHS [17] LEACH's stochastic cluster head selection algorithm is extended by adjusting the threshold T(n) denoted in equation (1), considering residual energy of the nodes, distance between the nodes and the base station and the number of consecutive rounds in which a node has not been a cluster head as parameters as follows: T (n) =

p  1 1 − p ×  r mod  p 

× [ E (i ) + (1 − D (i )) + (s div r )]

In Two-level Leach (TL-LEACH), CH collects data from other cluster members as original LEACH [2], but rather then transfer data to the BS directly; it uses one of the CHs that lies between the CH and the BS as a relay station [6].

∀n ∉ G

is the remaining amount of energy and

PEGASIS [8](Power Efficient Gathering in Sensor Information Systems) evolves from [2], but the structure of its cluster is a chain. When PEGASIS transmit data, the CH in a chain makes a token that is transmitted to another end of the chain to notice the last node to transmit.

T (n) = 0

(4)

Here residual energy factor is E(i)=(E residual (i)/E initial) residual

LEACH [2] offers no guarantee about the placement and/or number of cluster heads. In LEACH-C, an enhancement over the LEACH protocol was proposed [5].This protocol uses a centralized clustering algorithm and the same steady-state phase as LEACH. LEACH-C protocol can produce better performance by dispersing the cluster heads throughout the network.

In Energy efficient distributed clustering algorithm on coverage (ECAC)[7] the redundancy degree of coverage and nodes residual energy are considered in the cluster head selection.

∀n ∈ G

where E

III. RELATED WORK Energy-LEACH protocol improves the CH selection procedure. It makes residual energy of node as the main metric which decides whether the nodes turn into CH or not after the first round [4].

(5)

1st Int’l Conf. on Recent Advances in Information Technology | RAIT-2012 |

Based Energy Clustering (BEC) determines the number of optimal cluster-heads in a network and considers residual energy in the stage of cluster-heads selection [9].But it does not consider the distance of nodes from Base station. PECRP (Power Efficient Clustering Routing Protocol) is suitable to long distance and complex data transmission [10].It improves the mechanism in electing CHs of LEACH [2] and uses multi-hop data transmission. Low Energy Adaptive Clustering Hierarchy with Deterministic Cluster-Head Selection [11] extends LEACH’s [2] stochastic cluster head selection algorithm by a deterministic component.

IV. PROPOSED APPROACH A. Network Model For our proposed model, we adopt a few reasonable assumptions of the network model based on [8][17] as follows: (i) The base station is fixed at a far distance from the sensor nodes. (ii) The sensor nodes are homogeneous and energy constrained with uniformly energy. (iii) No mobility of sensor nodes. (iv) All nodes are able to reach BS. (v) Nodes RAM size should be sufficient enough to store the distance of the nodes from Base station. B.

Radio Energy Dissipation Model

In LEACH[2], Each CH directly communicates with BS no matter the distance between CH and BS. It will consume lot of its energy if the distance is far. On the other hand, Multihop-LEACH protocol selects optimal path between the CH and the BS through other CHs and use these CHs as a relay station to transmit data over through them [12].

In order to predict the performance of our proposed model, a simple model for the radio hardware energy dissipation is used where the transmitter dissipates energy to run the radio electronics and the power amplifier, and the receiver dissipates energy to run the radio electronics, as in [5].

In VLEACH protocol [13], besides having a CH in the cluster, there is a vice-CH that takes the role of the CH when the CH dies .

Fig.1 shows the Radio Energy Dissipation Model. For the experiments described here, both the free space and the multi path fading channel models were used, depending on the distance between the transmitter and the receiver. If the distance is less than a threshold, the free space (fs) model is used; otherwise, the multi path (mp) model is used.

LEACH’s [2] stochastic cluster head selection algorithm is extended in [14] by modifying the probability of each node to become cluster-head based on its required energy to transmit to the sink. LEACH-SM protocol [15] modifies LEACH [2] protocol by enhancing it with an efficient management of spares which has added the spare selection phase to LEACH. During this phase each node decides in parallel whether it should become an active primary node, or a passive spare node. The nodes that become spare go asleep, while the WSN as the whole maintains the required above-threshold target coverage. EECH (Energy Efficient Clustering Hierarchy) [16] evolves from LEACH [2], but it considers node’s energy and ensures that nodes with more energy have a higher probability than nodes with less energy in cluster head selection. Moreover Cluster heads are in the form of Multihop when they communicate with the base station. In EECHS [17] it considers residual energy of the nodes, distance between the nodes and the base station and the number of consecutive rounds in which a node has not been a cluster head as parameters in time of cluster head selection.

Figure 1. Radio Energy Dissipation Model

Thus, to transmit a k-bit message a distance d, the radio expends: ETx (k,d) = E Tx-elec (k)+ E Tx-amp(k,d) ETx (k,d) =

Eelec *k + ε fs* k *d2

if d