Incorporating Fault Tolerance in LEACH - Semantic Scholar

ISSN:2249-5789 Rudranath Mitra et al, International Journal of Computer Science & Communication Networks,Vol 2(3), 380-384

Incorporating Fault Tolerance in LEACH Protocol for Wireless Sensor Networks Rudranath Mitra1 , Anurupa Biswas2 Department of Information Technology Heritage Institute of Technology Anandapur,Kolkata-700107.INDIA. [email protected]

Abstract Routing protocols have been a challenging issue in wireless sensor networks. WSN is one of the focussed are of research because of its multiaspect applications. These networks are selforganized using clustering algorithms to conserve energy. LEACH (Low-Energy Adaptive Clustering Hierarchy) protocol[1] is one of the significant protocols for routing in WSN. In LEACH, sensor nodes are organized in several small clusters where there are cluster heads in each cluster. These CHs gather data from their local clusters aggregate them & send them to the base station. On the LEACH many new schemes have been proposed to enhance its activity like its efficiency, security etc. In this paper the fault tolerance issue is being incorporated. Key words: Cluster-head, CH, BS, LEACH, fault tolerance.

heads must be an autonomous, distributed process. This is achieved through LEACH.

Fig.1 1. Introduction A clustered architecture organizes the sensor nodes into clusters, where each cluster is governed by a cluster-head. The nodes in each cluster are involved in message exchanges with their respective clusterheads & these CHs send messages to their respective BSs, which is usually an access point connected to a wired network. Fig. 1 represents a clustered architecture where any message can reach the BS by at most 2 hops. Clustering can be extended to greater depths hierarchically. Clustered architecture is specially useful for sensor networks because of its capability for data fusion. The data gathered together by all members of the cluster at the cluster-head and only the resulting information are sent to the BS. Hence sensor networks should be self-organizing as well as the cluster information & election of cluster-

Fig. 1 represents a clustered architecture where any message can reach the BS by at most 2 hops. Clustering can be extended to greater depths hierarchically. Clustered architecture is specially useful for sensor networks because of its capability for data fusion. The data gathered together by all members of the cluster at the cluster-head and only the resulting information are sent to the BS. Hence sensor networks should be self-organizing as well as the cluster information & election of clusterheads must be an autonomous, distributed process. This is achieved through LEACH. LEACH is a clustering-based protocol that minimizes energy dissipation in sensor networks. LEACH randomly selects nodes as cluster-heads & periodic reelection for CHs is performed. It helps in energy dissipation among nodes in the network instead of depending on only one node (cluster-

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head). Each iteration of selection of CHs is called a round. The operation of LEACH is split into two phases: Set up & Steady. During the set up phase, each sensor node chooses a random number between 0 & 1. If it is lower than the threshold for node n, T(n), the sensor node becomes a cluster-head. The threshold T(n) is calculated as [2]:

Where P is the desired percentage of nodes which are CHs, r is the current round, and G is the set of nodes that has not been CHs in the past 1/P rounds. It ensures that all nodes eventually spend equal energy. After selection the CHs advertise their selection to all other nodes. All nodes chooses their nearest CH after receiving advertisements based on the received signal strength. The CHs then assign a TDMA schedule for their cluster members. This allows the sensor nodes of the cluster to turn off their transceiver except at the time slot allocated to them. Therefore it is saving considerable energy. During the steady phase, data transmission takes place based on TDMA schedule and the CHs perform data aggregation/ fusion through local computation. The BS receives only aggregated data from cluster-heads, leading to energy conservation. After a certain period of time in the steady phase CHs are again selected through the set-up phase. LEACH has been come out to be primary clustering protocol in the WSNs as well it has shown energy efficiency & effectiveness [3][4][5]. Hence LEACH has been chosen as the plot for implementation of fault tolerance.

2. Related Works The idea proposed in LEACH has been an inspiration for many hierarchical routing protocols,

although some protocols have been independently developed. Since sensor nodes are often placed in harsh zone [6], sensor nodes area prone to failure. Supposed if a cluster-head is faulty it can leave a cluster disconnected from the base station until the network reorganizes again. So we see fault tolerance problem is a very big problem in WSN. Several works has been done on fault tolerance over many clustering algorithms. One fault tolerance approach has been discussed in [7]. Here also the research work is done on LEACH. Here fault recovery is suggested in two ways: inter-cluster recovery & intra cluster recovery. Another research work on fault tolerance is discussed in [8]. Here a Dynamical Jumping Real-time Fault-tolerant Routing Protocol (DMRF) has been proposed. Once node failure, network congestion or void region occurs then the transmission mode will switch to jumping transmission mode leading to reduced transmission delay and guarantees the data packet to be sent to its desired destination within the specified time limit. Each node can dynamically adjust the jumping probabilities to increase the ratio of successful data transmission by using feedback mechanism. This mechanism results in reduced effect of failure nodes, congestion and void region and reduced transmission delay, reduced number of control packets and higher ratio of successful transmission. One more fault tolerant work is discussed in [9]. Basically, WSNs faces resource limitations, high failure rates and fault caused by wireless channels & wireless sensor nodes. It increases the reliability & robustness of the network by creating a backup path for every node on a main path of data delivery. When a node gets failure it immediately applies its backup path as the main path for data delivery of next incoming packets. This protocol reduces the number of dropped data packets and increases robustness of the entire network by maintaining the continuity of data packet transmission even in presence of faults.

3. Proposed Scheme In this scheme, fault is detected in a general way that if no response comes from the CH to BS or the subordinates then it is considered that the cluster-

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head is faulty and is become unable to transfer data.According to this scheme, there may be tworecovery mechanisms:Replace the faulty cluster-head by the next highest energy node in the cluster. Maintain two cluster-heads in each cluster by using token.

faulty, CH1 is responsible for gathering all the information from the subordinates to fuse the data & send to BS. So, until CH1 gets faulty i.e., CH1 is working properly, CH2 gets all the data from the nodes those are sending data to CH1 but CH2 is receiving data only, not sending any reply to those nodes. To make all the nodes know that the CH2 is alive i.e., not faulty, CH2 will periodically send a ping message to all the nodes. When CH1 gets faulty, then CH2 becomes responsible for the same activities that CH1 was doing. That means till then CH2 will be gathering all the information from the subordinates to fuse the data and send them to the BS. In case if CH2 becomes faulty while CH1 was working properly, then next highest energy node will be selected as CH2 & will act as that mentioned earlier. When CH1 has already become faulty and CH2 is playing the role of CH1, then also the next highest energy node will be selected as CH2. The entire procedure is pictorially well described in fig.2. When both CH1 & CH2 will stop working simultaneously by chance, then according to fig.2 the entire process has to be begun, that means from the advertising phase. If some of the subordinate nodes are faulty, then we can implement redundancy of subordinates. The expense to maintain this much of redundant nodes will be greater than the expenditure of maintaining two cluster-heads.

4. Fault Detection Algorithm 1. 2.

3.1. Illustration To avoid redundancy effect one token will be passing in between the two cluster-heads. When CH1 is active then the token will be kept by that CH (means CH1) and CH2 will not hold any token then. CH2 will have all the replica information from the communicating nodes. Until CH1 gets

3. 4. 5. 6. 7.

Initialize CH1 & CH2 & subordinates IF no response comes within a TDMA slot THEN Set CH1 as Faulty ELSE For CH2 IF no ping message comes periodically THEN Set CH2 as Faulty

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challenging issues in WSN. In some papers the jumping transmission mode is explored to guarantee real-time and fault tolerant characteristics. Some feedback mechanisms are used to enhance successful transmission ratio.

5. Results

LEACH is one of the most important & significant protocols for research issues in WSN. Through simulation it is shown that significant improvement is achieved in coverage and fault tolerance with a minimal trade-off in terms of reduced network lifetime.

8. Acknowledgements

LEACH

Fault Tolerant LEACH

We express our sincere gratitude to the Head of the Dept. and the members of the Research Team, Dept.-of-Information Technology,Heritage Institute of Technology.We do also acknowledge Smt. Baby Mitra,Sudeshna Chatterjee,Doel Mitra and Peali Juva for constant support and encouragement.

Network lifetime

Very Good

Near to LEACH

9. References

Fault Detection Capability

No

Yes

Fault Recovery Capability

No

Yes

6. Comparative Study

7. Advantages 1.

2.

3.

It is capable of avoiding incorporating redundancy of sensor nodes and paths into clusters in WSN. By avoiding redundancy, it is capable of incurring expenditure of maintenance of the redundant nodes and paths. Since LEACH is already a significant protocol in WSN due to its several applications, incorporating fault tolerance in LEACH makes LEACH more significantly tempting protocol in WSN research issue.

8. Conclusion Several new schemes for fault tolerance have been proposed on clustering algorithms in WSN because fault tolerance is one of the most

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