ENERGY EFFICENT ROUTING PROTOCOL IN WIRELESS SENSOR NETWORK

ENERGY EFFICENT ROUTING

PROTOCOL IN WIRELESS SENSOR

NETWORK

SASMITA SAHOO

sahoo_sasmita1@yahoo.com

BISWA MOHAN ACHARYA

Asst. Professor, Dept. of Computer Applications, ITER, SOA University, Bhubaneswar, Orissa, India.

biswa.acharya@gmail.com

Abstract:

Wireless sensor networks consist of small battery powered sensor nodes with limited energy resources. The area of wireless sensor networks is now attractive in the research area due to its applications in many fields such as defense security, civilian applications and medical research etc. In wireless sensor networks, the important task is to periodically collect data from an area of interest for time-sensitive applications. Then the sensed data must be gathered and transmitted to a base station for further processing to meet the end-user queries. Routing is a serious issue in WSN due to the use of computationally-constrained and resource-constrained micro-sensors. Once the sensor nodes are deployed replacement is not feasible. Hence, energy efficiency is a key design issue to improve the life span of the network. Since the network consists of low-cost nodes with limited battery power, it is a challenging task to design an efficient routing scheme that can offer good performance in energy efficiency, and long network lifetimes.

Keywords- Chain; clustering; energy-efficiency; network lifetime; wireless sensor networks.

1. Introduction

Wireless sensor network is an important technology that will change the world [11]. Wireless sensor networks consist of hundreds to thousands of low-power multifunctioning tiny sensor nodes which operate in an inaccessible environment, with limited computational and sensing capabilities. In recent developments the low-power wireless integrated micro sensor technologies have made these sensor nodes available in large numbers, at a low cost which is employed in the area of applications [2]. WSN is widely used in military and national security, environmental monitoring, home automation, traffic control, health application and many other fields. The main job of sensor network is to periodically collect data from area of interest and then sends back the data to the Base Station (BS) for analysis, which is usually located far from the target area [5]. The most restrictive factor in the life-time of wireless sensor network is limited energy resource of the sensor nodes. So energy consumption is main requirement in the design of sensor network protocols and algorithms. As the sensor nodes are equipped with small, limited power capacity batteries, the network should be energy efficient to increase the life span of the network [2,9]. Wireless sensor network design also demandsrequirements like fault tolerance, scalability, production costs, and reliability. So It is difficult that the designer takes consider these factors when designing protocols and algorithms in wireless sensor networks [2].

nodes. So that energy consumption of the sensors is balanced. In this paper Sensors are grouped into several clusters. In every cluster, a routing tree is constructedfor data transmission. One sensor node is selected as acluster head in every cluster. This cluster head selection based on the residualenergy and this node remains as a cluster head for an optimal number of rounds. Among all cluster heads, arouting tree is also constructed. After an optimal number of rounds, new group of cluster heads are selected. Due to the hierarchical tree structure and all tasks done by a high energy base station our protocol requires less energy as compared to other protocols .All nodes in a cluster send the sensed data to their neighbor node instead of the cluster-head. Each node aggregates the data to reduce the amount of data transferred. The cluster-head fuses the data received from the member nodes within the cluster and then transmit them to the BS. Here, the cluster formation occurs after certain round.

In LEACH, sensor nodes are organized into local clusters. In each cluster one node is selected as cluster head. The cluster head receives data from all other sensor nodes within the cluster and then performs data aggregation on collected data and then transmits the aggregated data to the BS for analysis. LEACH has some drawbacks. Firstly, the cluster setup phase takes place at every round. Secondly, the complexity arises due to TDMA scheduling in transmission from the members to cluster head in transmission phase. Thirdly in LEACH the number of cluster heads varies from round to round due to the lack of global coordination among sensor nodes .So there is no balance in energy consumption among sensor nodes.

Then BCDCP provides an improvement over LEACH. A high-energy base station is used for balance cluster formation, cluster head selection and routing paths construction, perform randomized rotation of cluster heads, and other energy-intensive tasks in BCDCP. But in BCDCP setup phase i.e. cluster formation ,cluster head selection occur in every round .So it is more energy consumption.

In GSEN all cluster setup and routing path calculation are done by the sensor nodes themselves. GSEN has two phases – chain formation phase, data transmission phase. Several groups are formed in chain formation phase. One sensor node is selected as cluster head in each group. All nodes form a chain among them within the group. Then a high level chain is formed including all cluster head from every cluster .In this high level chain only One randomly chosen Cluster head sends data to BS in high level chain. If event occurs repeatedly then the sensor nodes do sensing, processing repeatedly .So that the nodes are die after some time .So this will not suitable for application where event occur repeatedly .In our work, we propose a hierarchical tree based protocol which will get better performance in energy consumption .

The remainder of the paper is organized as follows. A detail description of our approach is presented in Section 2. Finally, Section 3 presents a concluding remark.

2. Proposed Protocol

It operates in two major phases: 1. Set up phase

2. Data communication phase.

2.1. Set up phase

Cluster setup, cluster head selection, CH-to-CH routing path formation and schedule creation for each cluster are the main activities in set up phase .During set up phase; the base station receives information of the current energy status from all the nodes in the network. Based on this information, the base station first computes the average energy level of all the nodes. Then chooses a set of nodes, denoted as A, whose energy levels are above the average value. Cluster heads for the current round will be chosen from the set A. The nodes with sufficient energy get selected as cluster heads.

2.1.1. The Cluster and Chain Set-up Phase

The threshold is set as follows: P

T =

1- P×(r mod 1/p)

Where P is the cluster-head probability; r is the number of the current round.

The nodes that have not been cluster heads in the last 1/P rounds participate in the selection process. This algorithm ensures that every node in A becomes a cluster-head exactly once within 1/P rounds. In the LEACH the role of cluster-head circulates among sensor nodes .So it distributes the overhead among the sensor nodes in the network.. The distance between a sensor and the cluster-head in a cluster decreases while that between the cluster-head and BS increases as the number of clusters increases in a bounded region. An opposite phenomenon is observed when the number of clusters decreases. In the sensor network the distance from the cluster-heads to the BS and the distance from the sensors to the cluster head depend on the number of sensors and clusters, and size of target area. An optimal value of P, Popt, in terms of energy efficiency needs to be decided by taking the tradeoff between sensor-to-cluster-head and cluster-head-to-BS communication overhead. With Popt, the new threshold of node_n, Tnew(n), is decided as follows:

Popt

Tnew (n) =

1- Popt × (r mod 1/ Popt)

Tnew (n) = 0 ,

Once a node has selected itself as the cluster head, it informs all other nodes in the network. It first generates a cluster-head token. Then broadcasts an advertisement message (ADV) to the rest of the nodes. As announcement message, the message contains the node ID and a header identifying message. After receiving the advertisement messages, the non-cluster-head nodes compare the signal strengths. Then they decide to join the cluster-head of the highest signal power. Then each node transmits a join-request message (Join-REQ) to the cluster-head it selected. Here BS takes account into balanced cluster formation i.e. equal number of nodes within a cluster to avoid cluster head overhead. Cluster formation is complete and the chain formation step begins. Themain difference between our approach and LEACH isthat, in LEACH where cluster set-up takes place atevery round, our approach prefers to re-build clustersafter a certain number of rounds. Inside cluster nodes change their state from active to sleep mode so that all node not active always. After the clusters are formed, chains are constructed using the member nodes in each cluster. The cluster-head applies the shortest path algorithm to find the best route to each member node for chain construction. Inside cluster among non-cluster-head nodes, minimum spanning tree with degree constraint approach is applied to find the best route. The cluster-head nodes decide the order of cluster-head rotation and create the schedule after the chain construction is over. The schedule includes the scheduling information, order of cluster-head rotation. The schedule also allows the radio components of each non-cluster-cluster-head node to be turned off .So this minimize the energy consumption.

2.1.2. The cluster-head rotation

In LEACH, clusters are reconstructed at every round for load distribution among all the sensor nodes. A large energy is consumed in this process. In the proposed scheme, the role of cluster-head change among cluster in each round until next clusterformation phase is needed. So this approach improves the energy efficiency. In this proposed scheme the cluster-head transmits a token to the member nodes in the cluster to inform cluster-head change in the last frame of each round. Then the cluster-heads broadcast the schedule information to the member nodes in the cluster, which includes {node_id, rotation_number, next_node}. Here, node_id is unique identification of each node,

rotation_number is the order of the node to become the cluster-head, and next_node is the neighbor node to which data transmission occurs. For example, {20, 5, 16} indicates that node-20 is the 5th cluster-head and needs to send data to node-16. The initial set-up phase of the proposed scheme is equivalent to LEACH.

other nodes. So we introduce the degree constraint to each tree node to avoid the situation that a node will be connected with many other nodes .So this protocol uses the degree constrained minimum spanning trees. This tree formation algorithm starts with the cluster head. This cluster head node is treated both as a starting node. The starting node will broadcast a find-nearest-neighbor (FNN) message with largest transmission range to find the nearest live node among all nodes in a cluster. Once a node receives the FNN message, the node first checks that the message is sent by the node in the same cluster or not. If it is not from the same cluster, the message is ignored. Otherwise, the node sets a back off timer of t1 seconds. This t1 is in some range and depends on the signal strength of the received message. If the signal strength of the received message is more, t1 will be less. When the timer expires, the node sends back an acknowledgement (ACK) message with its node id to the starting node. If a node hears other ACK messages before its timer expires, it cancels its timer. When all tree nodes receive the ACK message, they will set a back off timer of t2 seconds. Again, t2 is relative to the signal strength of the received ACK message. When t2 expires, the node sends a confirmation (CFM) message with node ID to inform the node sent the ACK message to be the next starting node .Then link between them can be constructed. The above process will be repeated to find the next nearest live neighbor node until no live neighbors exist. To find the degree constrained MST is simple. First, let each node has a counter. This counter indicates the current degree of node. When a nearest live neighbor node replies with an ACK message to the starting node, some tree nodes will receive this message. Before the tree node sets a back off timer, it has to check if its current degree counter is less than the degree limitation d. If its current degree counter equals to d, then it does not need to set a back off timer to response the ACK message. When a link is established, the current degree counter will be incremented by one for both nodes connected by the link. When the above procedure stops, a degree constrained spanning tree with no nodes of degree greater than d is obtained for a set of sensor nodes.

Then routing path is constructed among cluster heads to send the data to BS. Then the routing paths are selected by connecting all the cluster head nodes using the minimum spanning tree with degree constraint that minimizes the energy consumption for each cluster head. Then randomly choosing one cluster head node to forward the data to the base station. This routing is a hierarchical cluster routing scheme to reduce energy consumption.

2.2. Set up phase algorithm

A is the set of node whose energy level above the average energy level of nodes.

Set up phase:

1. For (node _j Є A)

J<=S

2. Node_ j selects random number between 0 to 1.

3. if number smaller than threshold T.

4. Then the node_ j becomes cluster head.

End if

5. Cluster head_ j broadcasts adv msg along with id to all its non cluster head node _i.

6. Non cluster head node_ i compare the signal strength of cluster head j and decide to join the cluster head_ j of highest signal power and send the join _req msg to cluster head_ j.

7. Cluster is form.

8. for (all cluster_ k)

9. Then a routing path is established among cluster head_j to find best route using degree constraint minimum spanning approach .

10. Clusterhead_j broadcast the schedule information to member node _i within the cluster _k

This includes (node id, rotation number, next node).

3. The Data Communication Phase

The data communication phase consists of three activities: • Data gathering

• Data fusion • Data routing

After the clusters and the cluster head nodes have been identified, the base station chooses the lowest-energy routing path by the approach minimum spanning tree with degree constraint within the cluster to send the information from node to node to cluster head .Each end node in a chain starts to transmit the data to the next node .Each node receives data from the neighbor, fuses with itsown data, and transmits the data to the upstream neighbor inthe chain.

Then the routing paths are selected by connecting all the cluster head nodes using the minimum spanning tree with degree constraint that minimizes the energy consumption for each cluster head, and then randomly choosing one cluster head node to forward the data to the base station. The cluster-head transmits the data to theBS through the routed path after applying data fusion. After the data from all sensor nodes have been received, the cluster head performs data fusion on the collected data, and reduces the amount of raw data that needs to be sent to the base station. The compressed data, along with the information are then routed back to the base station via the CH-to-CH routing path with degree constraint created by the base station.

3.1. Data transmission algorithm

1. For (all node_ i)

Node_ i transmit the data to its neighbor node i of its routed path constructed using degree constraint minimum spanning approach .finally data sends to cluster head_ j of that cluster_ k.

2. for (all cluster head_ j)

Cluster head_ j fuse all received data with its own and transmit the fused data to neighbor cluster head_ j of its routed path constructed using degree constraint minimum spanning approach.

3 .Then fused data finally send to Base station.

4. Conclusion

In this paper, we propose a new centralized hierarchical tree based routing protocol in order to reduce the energy consumption. The energy efficiency is maximized by the rotation of cluster-head locally inside the cluster as clustering takes place after certain rounds. Also, degree constraint minimum spanning reduces energy consumption of thenodes.

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