AbstractGenerally the energy of each node in wireless sensor networks is restricted, energy efficient and energy evenly distributed route protocol is indispensable to prolong the lifetime of the network. Although Low-Energy Adaptive Clustering Hierarchy (LEACH) and protocols based on LEACH are all low-energy hierarchies, some nodes in network still quickly use up their limited energy, because cluster-heads (CHs) are selected randomly and the number of CHs is fluctuating heavily regardless of energy remaining in the nodes. In this paper, we develop and analyze a protocol which forms clusters like LEACH when first round or after one invalid node or more appear. During other rounds previous CHs can transfer the role of CH to the most energy nodes in corresponding clusters, instead of random reselection of CHs. The information of the residual energy of each node is reported to its cluster-head (CH) in data package at the end of the rounds before invalid one node appears. Moreover number of CHs could change with number of nodes alive. Simulation result shows that the protocol can maximize the time of the network without nodes using up energy, called no deaths period.

I. INTRODUCTION APID development of sensor technology, low-power electronics, and low-power radio frequency (RF) design have enabled sensors can be connected via wireless

network [1]. Wireless sensor network(WSN) consists of spatially distributed autonomous sensors to monitor physical or environmental conditions, such as temperature, sound, vibration, pressure, motion or pollutants and to cooperatively pass their data through the wireless network to a main location.

However, the development and design of WSN faces two important challenges which are communication bandwidth and limited energy. The energy of WSN is significantly more limited than a tethered network environment. Therefore, designing energy efficient routing protocols for WSNs becomes an important technique addressed to alleviate this problem.

There have been some energy efficient protocols developed for WSN. Among these protocols, LEACH that is first proposed by W. B. Heinzelman is one of the first distributed cluster formation algorithms in WSN [1] [2]. Then

Jian Li is with School of Hydropower and Information Engineering,

Huazhong University of Science and Technology, Wuhan, Hubei, 430074, China. (e-mail: anjili@163.com)

Jianzhong Zhou (corresponding author) is with School of Hydropower and Information Engineering, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, China. (phone: 027-87543127; fax:027-87543127; e-mail: prof.zhou.hust@263.net)

Jian Xiao is with School of Hydropower and Information Engineering, Huazhong University of Science and Technology, Wuhan, Hubei, 430074, China.

numerous hierarchical protocols derived from LEACH were designed. However, the clustering strategy of LEACH mainly depends on the randomly selecting of CHs. As a result, the number of CHs is fluctuating and the nodes residual energy is ignored [2]. LEACH-B architecture, which is designed by Mu Tong and Minghao Tang, avoids the defects of LEACH: the probability in selecting CHs is equivalent, without considering the remaining energy of nodes; the number of CHs is fluctuating heavily [2]. But LEACH-B still cannot remove the probabilistic CHs selecting. Energy-LEACH protocol selects CHs by comparing energy of each node and the scheduled energy value [6]. But, Energy-LEACH does not describe how the network gets scheduled energy value and the nodes with more residual energy.

II. LEACH AND LEACH-B PROTOCOL ARCHITECTURE

A. Energy Dissipation Model We assume a simple model for the radio hardware energy

dissipation where the transmitter dissipates energy to run the radio electronics and the power amplifier, and the receiver dissipates energy to run the radio electronics (this model is used in many works like [1, 9]), as shown in Fig 1.

d)(l,ETx

lEelec n

amp dl lEelec

(l)ERx

Figure 1 energy dissipation model For the experiments described here, both the free space

( 2d power loss) 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. Thus, to transmit an l-bits message over a distance d, the radio expends (1):

d)(l,E(l)Ed)(l,E ampTxelecTxTx += (1)

+

2fs d or

4mp d , depends on the distance to the

receiver and the acceptable bit-error rate. To receive 1-bit message, the radio expends (4):

elecelecRxRx El(l)E(l)E == (4) It is also assumed that the radio channel is symmetric,

which means the cost of transmitting a message from A to B is the same as the cost of transmitting a message from B to A. The used parameter values in our work are giver in the following table I.

B. LEACH Protocol LEACH assumes that the initial energy of every node is the

same. And the all nodes in area are divided into several clusters with one node as the CH in every cluster.

Its network topology could be shown in Figure 2.

Figure 2 Topology structure of LEACH

This protocol provides a conception of round. Each round contains two phases: cluster setup phase and steady phase.

1) In setup phase, each node decides whether or not becomes a CH randomly for current round by the method below, and the CHs send broadcasting messages to all the normal nodes, then every normal node adds to one cluster, of whose head is the nearest to this normal node among the CHs, and then the normal node sends a message to the corresponding CH. Here, the distance between CH and normal node is judged by the strength of broadcasting message signal received by normal node. The CH allocates the communication time slot for each member node in the cluster based on TDMA (Time Division Multiple Access) [3].

2) During stead phase, the non-cluster-head nodes transmit data to their CHs. After data fusion the CH sends data package to the base station (BS or sink node) with just one hop. Because of the data aggregation and the communication to sink node, the energy consumption in CH is high. So the CHs will be reelected in the next round which is essential to evenly distribute the energy load among all nodes [4].

The method of CH selecting in LEACH can be expressed as follows: each node chooses a number between 0 and 1 randomly, If the number is less than the threshold value T(n) ,the node becomes CH. T(n) is shown as equation(5):

=

otherwise, 0

Gn,))p1p(rmod(1

pT(n) (5)

Where P is the percentage of CHs to all nodes, and r is the round number, r mod (1/p) stands for the number of nodes

selected as CH for this round, and G is the set of nodes which have not been elected as CH nodes previously. When r=0, the possibility of each node becoming CH is P. If one node becomes CH in the first r rounds, it can be no longer re-elected in the future (1/P-r) round, which enhances the possibility of other nodes to become a CH. After 1/p rounds, all nodes have a possibility of P to be a CH once again, over and over again [3] [5].

C. LEACH-B Protocol Optimal CHs amount will save the energy consumption

and prolong the lifetime of network. LEACH-B protocol [2] can ensure networks optimization of number of CHs.

LEACH-B works similarly as LEACH. There is a second selection of CHs after the first in set-up phase.

The first selection works as LEACH. At the beginning of the second selection, we compare the

number of CHs produced in first selection with np (n is the total number of network and p is the percentage of CHs of n). If the number of CHs is less than np, a timer is set for every normal node. When the timer expires, the normal node with shorter time interval broadcasts a message to inform of its CH role. And the value of time interval is set as (6):

Ekt = (6) Where k is a factor, and E is value of the residual energy

of each normal node. If the number of CHs is more than np after first selection,

some CHs with less energy could be changed to normal nodes.

Then the formation of cluster and the steady phase is same as LEACH.

D. Problems of LEACH and LEACH-B Firstly, the number compared with threshold T(n) is

generated randomly. It leads to the stochastic selecting of CHs.

Secondly, in LEACH the remaining energy of nodes is ignored when selecting CHs. And the probability of every node to become CH is equivalent. As a result, those nodes with less remaining energy may be selected as CHs and quickly run out of energy that leads the network become invalid in a short time.

Thirdly, the number of CHs fluctuates wildly and stochastic distribution of CHs remains unbalanced in area of network in LEACH protocol. Thus energy dissipation increases in entire network [7].

Fourthly, LEACH-B and LEACH are both distributed algorithms, that is, nodes make autonomous decisions without any centralized control.

III. PROPOSED PROTOCOL To prolong the lifetime of the network, selecting a node as

CH with maximum energy in the partial area is a feasible way, not as the LEACH which selects CH by comparing the number randomly generated between 0 and 1 and the threshold T(n).

The operation of proposed protocol is divided into rounds too. And each round has three states, as shown in figure 3.

705

cc

Figure 3 2 states of LEACH & 3 states of proposed protocol

To avoid the defects of LEACH, we propose a protocol architecture whose CH selecting is deterministic and without random. The strategy of cluster head selecting is described as follow:

In first round or if the number of nodes whose energy has been used up is greater than 0, CHs are selected by the way as LEACH protocol.

After the first round and there is no node running out of energy, residual energy must be considered when selecting CHs every round. At the end of the previous round, the normal nodes send messages reporting residual energy of themselves to the CHs. In current round, the CH deals with the messages reporting about remaining energy and chooses the node with most energy as CH for current round. Then the CH of previous round sends a message to this node to inform it of the role as CH for current round.

Then the new CHs broadcast messages that inform CHs role. And normal nodes receive these messages and add to the cluster whose head is nearest. In the steady phase, every normal node sends message with data to the corresponding CH, then the head aggregates the data and sends the resultant data to BS. At last is the phase of reporting residual energy and the normal nodes report the residual energy of themselves to their CHs.

When operations above have been completed, the next round is started. The flow chart of the operations is as Figure 4.

The procedure of the proposed protocol can be described as follow:

1) In first round (or round, r is non-negative integer) or after number of the nodes exhausting energy is greater than 0,

CHs could be selected as the way in LEACH. 2) The CHs may be labeled as C_i, normal node labeled as

N_j. Then heads broadcast messages to other nodes to inform of their becoming CHs. 3) Every normal node N_j calculates the distance to all

CHs through strength of received broadcasting messages signal

from heads. And normal node sends a message called requesting joining in the cluster to the nearest CH. 4) After CH receives requesting joining in the cluster message, it sends message called replying requesting joining the cluster to its corresponding normal nodes.

5) If normal nodes successfully receive replying requesting joining the cluster messages, a normal node adds to a corresponding cluster successfully. Otherwise, the procedure steps to 3).

6) In the steady phase, normal nodes send data packages to their corresponding CHs, and the heads fuse the data packages and send to base station.

Figure 4 Flow chart of proposed protocol

7) In the reporting residual energy phase, all of normal nodes alive send the data describing remaining energy to the heads corresponding.

8) A round is ended up. If the number of the nodes using up energy is equal to total number of network, out of all cycles.

9)At beginning of r+1(r0) round, number of the nodes exhausting energy (called dead nodes) is checked and if it is equal to 0, information about residual energy collected at CHs is processed (handled) and choose a node as CH whose residual energy is the most. Then the procedure steps to 2). And if the number of the dead nodes is not equal to 0, the procedure steps to 1).

Number of CHs could change with total number of network nodes alive, in order to get the optimization of energy consumption.

And the schematic diagram of the procedure for selecting CHs without random is described in the Figure 5 to Figure 9.

706

Figure 5 Phase of residual energy reporting in the (r-1) round

Figure 6 In thr round, the residual energy of CHs is compared with normal nodes and the nodes with most energy N2 and N5 are selected; C1 and C2 send messages to N2 and N5 to inform them of becoming heads.

Figure 7 In thr round, the new CHs broadcast.

Figure 8 In thr round, the normal nodes determine its cluster by distance based on the received signal strength and send request message.

Figure 9 In thr round, the new head send replying request joining to the members of the cluster, and cluster is set up. Then followed by steady phase and reporting residual energy phase.

IV. ANALYSIS AND SIMULATION OF LEACH AND PROPOSED PROTOCOL

A. Parameters for Simulation To evaluate the performance that proposed protocol could

reduce energy consumption and prolong lifetime of network, we simulated both LEACH and proposed protocol by Matlab. And the parameters are set as the table I bellow.

TABLE I PARAMETERS USED IN SIMULATION

Parameter Value Unit

Origin of coordinates (0,0) Area of nodes distributed 200200 m2

Coordinate of base station (100,250) Total number of all nodes 300 Initial energy of every node 0.5 J Length of packages for

reporting residual energy 100 bit

Control package length 100 bit Data package length 4000 bit ETx 5010-9 J ERx 5010-9 J

fs 1010-12 J

mp 0.001310-12 J

EDA 510-9 J Percentage of node becoming

into CH 0.05

Time for simulation 1800 round

B. Figure and Analysis By comparing the procedure of LEACH and proposed

protocol, initial set of both LEACH and proposed protocol is the same, too the mechanism of energy consumption in steady phase. The difference between two protocols is that proposed protocol has phase of reporting residual energy and its cluster selecting is nonrandom but based on the report packages.

In LEACH, the energy is dissipated as six steps: 1) The CHs send broadcasting packages; 2) Normal nodes receive broadcasting packages; 3) Normal nodes send request joining packages; 4) CHs receive request joining packages; 5) CHs send reply request joining packages;

707

6) Normal nodes receive replying request joining packages.

However, in proposed protocol procedure of energy dissipating is divided into seven steps: the first six steps are the same as LEACH, but one more step is that the normal nodes send reporting residual energy packages to CHs corresponding at the end of the round while there is no dead node.

Figure 10 Total energy

The curves of total residual energy over time (rounds) as Figure 10 could proves the difference of specific circumstances of energy dissipating among LEACH and LEACH-B and proposed protocol. As shown, the proposed protocol consumes less energy than LEACH and LEACH-B in the former about 430 rounds, but more after about 450 rounds. It gets rid of randomness, and cluster selecting is partly based on how much residual energy is. As a result, the energy load of the proposed protocol can be more evenly distributed.

Figure 11 Number of residual nodes

Figure 11 shows number of residual nodes over time. We can see that in proposed protocol, the length of period is longer than LEACH and LEACH-B, during which there is no node using up energy. And the former is twice the LEACH and LEACH-B. However, the death rate of the nodes is higher than LEACH and LEACH-B after the first dead node, and the

three curves intersect at points where there are only about 170 nodes alive. So the proposed protocol is more suitable to application with requirements on number of effective nodes.

V. CONCLUSIONS This paper compares LEACH and another protocol

LEACH-B based on LEACH, and analysis the cluster selecting algorithms. Then we propose a selecting algorithm based on reporting residual energy packages without randomness, while LEACH and LEACH-B select CHs randomly. Although reporting residual energy will consume some energy, CH selecting getting rid of randomness can prolong the period during which there is no node using up energy. The simulation proved this.

ACKNOWLEDGMENT This research is supported by National Natural Science

Foundation of China (NSFC) (Grant No. 51079057), Key Project of National Natural Science Foundation of China (Grant No. 51039005), the research funds of University and college PhD discipline of China(Grant No. 20100142110012).

REFERENCES [1] W. Heinzelman, A. Chandrakasan, H. Balakrishnan, An

Application-Specific Protocol Architecture for Wireless Microsensor Networks, IEEE Trans. Wireless Communications, vol. 1, no 4, pp. 660-670, Oct. 2002.

[2] Mu Tong, Minghao Tang, LEACH-B:An Improved LEACH Protocol for Wireless Sensor Network, Wireless Communications Networking and Mobile Computing (WiCOM), Chengdu, 2010, pp. 1-4.

[3] Xinhua Wu, Sheng Wang, Performance Comparison of LEACH and LEACH-C Protocols by NS2, Distributed Computing and Applications to Business Engineering and Science (DCABES), HongKong, 2010, pp. 254-258.

[4] Weichao Wang, Fei Du, Qijian Xu, An Improvement of LEACH Routing Protocol Based on Trust for Wireless Sensor Networks, Wireless Communications Networking and Mobile Computing (WiCOM), Beijing, 2009, pp. 1-4.

[5] W. Heinzeman, A. Chandrakasan, H. Balakrishnan, Energy-efficient routing protocols for wireless microsensor networks, Proceedings of the 33rd Annual Hawaii International Conference on System Sciences, Maui, 2000, pp. 534-546.

[6] Xiangning Fan, Yulin Song, Improvement on LEACH Protocol of Wireless Sensor Network, 2007 International Conference on Sensor Technologies and Applications, Valencia, Spain, 2007, pp. 260-264.

[7] W. T. Hernzelman, J. Kulik, H. Balakrishnan. Adaptive protocols for information dissemination in wireless sensor networks, MobiCom '99 Proc. 5th Annual ACM/IEEE Int. Conf. Mobile Computing and Networking (MobiCom 99), Washington, 1999, pp. 174-185.

[8] Tao Lu, Qingxin Zhu, Luqiao Zhang, An Improvement for LEACH Algorithm in Wireless Sensor Network, 2010 5th IEEE Conf. Industrial Electronics and Applications, Taichung, 2010, pp. 56-59.

[9] O. Zytoune, Y. Fakhri, D. Aboutajdine, A Balanced Cost Cluster-Heads Selection Algorithm for Wireless Sensor Networks, International Journal of Computational Science, Vol. 4, pp. 21-24, 2009.

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