Energy Efficient Routing in Wireless Sensor Networks

Gunti Spandan1, C R Manjunath2, Nagaraj GS3

1,2Dept of CSE, SET, Jain University, 3RVCE, VTU spandangunti@gmail.com , manjucr123@gmail.com , nagarajgs2000@yahoo.com

Abstract:Wireless Sensor Networks present a great potential in monitoring systems. Routing problem is one of the most important issues in a wireless sensor network (WSN).Any routing protocol designed for wireless sensor networks is should take into consideration, the challenging factors like fault tolerance, energy efficiency, scalability, latency, power consumption and network topology. The stringent requirement of energy budget has been an emerging issue in the design specification for a wireless sensors network (WSN). In this paper we present a study on demand &cluster multicast routing protocols with energy-efficiency perspective.

Keywords: multicast, routing, wireless sensor networks, energy efficient. I - Introduction

Wireless sensor network(WSN) is a multi-hop wireless networks consists of a large of small-size, low-cost and low-power sensor nodes which are capable of sensing, computation and communication. WSN take advantage of deployment rapidly and strong survivability without fixed network support,but also with features of dynamic topology structure and energy resources are limited and so on.The application of WSN technology is a revolution of perceived and collection of information andused for various applications such as habitat monitoring, automation, and agriculture [1].

Routing in WSNs is very challenging due to the inherent characteristics that distinguish these networks from other wireless networks like mobile ad hoc networks or cellular networks.Sensor nodes are tightly constrained in terms of energy, processing, and storage capacitiesthey require careful resource management. Multicast is the communication paradigm of one-to-many or many-to-many, based on defined groups and constituted by members, whose interest is to receive/share the same information for a specific application.Multicast routing is to find a multicast tree which is rooted from the source and spans all destination nodes.The whole routing process includes two phases. The first phase is to seek a minimal energy path from the sink to the access point based on the idea of dynamic programming. The second phase is to search for a broadcast tree between the access point and the destination nodes in the multicast region [2].

Energy Efficient Routing method is proposed for a static wireless sensors network, which consists of a large number of energy-constrained sensors and a few hubs as the cluster heads of sensors. Since each battery-powered sensor only has limited energy resource and the battery recharge or replacement is impractical, a network with energy-aware design becomes important to achieve the desired lifetime performance.

Energy-efficient multicast routing protocol is of paramount importance for many new applications being developed for the resource scarce WSN.

II - MULTICAST AD HOC ON-DEMAND DISTANCE V ECTOR(MAODV)

MAODV like DSR has the same on demand routing characteristics, but uses an entirely different approach for maintaining routing table information. As MAODV belongs to the family of on demand routing protocol, so it follows the conventional scheme of maintaining routing table i.e. only one entry will be made for each destination. The entry made contains two information's, first one is it will update its destination with the next hope and then the next hope will update its sequence number which shows that how recently this node has updated.

MAODV also updates the upstream link if any link associated against this entry goes down. MAODV also uses the same broadcasting mechanism as used by the DSR for discovery within the network but it is different from AODV as it only receives route reply from those nodes which belongs to a family of multicast group.

Figure 1 MAODV Joining Process- Image reproducedThe group leader broadcast a HELLO message to all the nodes and they update their request table upon this group HELLO message. If a new node is interested to be a part of join this group, initially it will generate a route request packet (RREQ). The node unicast this request if it already knows the group leader address otherwise it will be broadcasted. The group leader or any other node of the requested group having a grater sequence number than that of the RREQ packet is allowed to respond. As the message is broadcasted the members of the group or the group leader will receive several RREQ packets but it will consider only one having the highest sequence number and least hope count. After selecting the request packet, it unicast a route reply packet to the desired node. This replying packet consists of the sequence number which is

recently updated and the distance of the node from the group leader. The requesting node at its end also receivesnumerous replies from different nodes and group leader but selects only one having the shortest distance among all RREP packets and most recently received. After selecting the most suitable route it generates a multicast activation packet (MCAT) to its neighbor node to enable the desired route.Figure2 shows the node joining process of MAODY.

III - THRESHOLDSENSITIVEENERGY EFFICIENT SENSOR NETWOR K ( TEEN)

Threshold sensitive Energy Efficient sensor Network (TEEN)[5] belongs to on-demand routing protocols category and mostly used for time crucial applications. In TEEN, nodes have two levels of cluster heads and also they follow hierarchical clustering design. After nodes have selected their cluster head, user needs to manually enter the attribute values, which will be broadcasted by cluster head in form of two parameters soft threshold and hard threshold.

The sensor nodes will start transmitting data when minimum threshold value is greater than hard threshold. Another variable called sensed value is used for transmitted data. Teen saves data continuously. The soft threshold also saves energy by reducing the transmission, when there no or little change in the attribute value. Cluster head will definitely consume more energy than a normal node because it needs to do extra processing.

Figure 2 Operational Flow of TEENThe biggest disadvantage of this protocol is that when hard threshold value is higher than sensed value there will be no transmission to clustered head from node, so the cluster head will have no information updation even if the node is no more in network. This problem can easily be addressed by fixing soft threshold to as minimum value as possible even though it would increase energy consumption but nodes sensibility will also be increased. This protocol uses Time Division Multiple Access (TDMA) as a scheduler to send data between nodes and their cluster heads.Figure 2 shows operational flow diagram of TEEN protocol.

IV - Adaptive Periodic Threshold-sensitive Energy Efficient sensor network protocol (APTEEN)

APTEEN, is a hybrid protocol proposed in [5] for both periodic data collection and time critical events. In this, cluster is formed with 1st level and 2nd level cluster

heads. After selecting the cluster head (CH) it receives the attribute from the user. The CH broadcasts the attribute, hard threshold (HT), soft threshold (ST), schedule and count time (CT) parameters to the cluster members. The sensor nodes sense continuously. If the sensed value is above the HT it is stored in the internal variable (SV) and transmitted to the CH through the TDMA schedule assigned for it. All the clusters formed here may not have uniform number of sensor nodes. The cluster formed with maximum number of nodes requires more time to aggregate the captured data from nodes and transmit to BS than the cluster with minimum number of nodes.

Suppose in any cluster, adjacent nodes have the similar sensed data to transmit then those nodes are formed as a pair. Only one node from the pair will respond to the query while the another node goes to sleep mode. The node which responds to the query is considered as active node and the other node which goes to sleep mode is considered as sleep node. This protocol supports one time query, historical query and persistent query. The BS needs to respond to nodes query only after receiving the data from all the CHs.

As the cluster head of cluster with maximum members require more time to communicate with BS a modified TDMA schedule is assigned as per which BS needs to wait until data from CH of cluster with more members reaches it. Apart from responding to time critical events, the nodes were also forced to transmit data to CH at periodic intervals as CT even though the sensed data does not exceed the threshold value. Where CT is the maximum time period between two successive reports sent by a node. Due to this periodic transmission, frequent updates of the nodes sensed value are transmitted to its CH. In this protocol the energy consumption can be reduced by properly selecting the CT and threshold values.

CDMA schedule is used to avoid collisions during cluster heads communicating with BS.The attributes can be changed during the every cluster head change time. The main drawback ofthis protocol is the additional complexity required to implement the threshold functions and CT.

V - SPEED Protocol

SPEED maintains a desired delivery speed across sensornetworks by both diverting traffic at the networkinglayer and locally regulating packets sent to the MAC layer.It consists of the following components: An API, A neighbor beacon exchange scheme, A delay estimation scheme, the Stateless Non-deterministic Geographic Forwardingalgorithm (SNGF), A Neighborhood Feedback Loop (NFL), Backpressure Rerouting, Last mile processingAs shown in Figure 4,.SNGF is the routing module responsible for choosing the next hop candidate that can support the desired delivery speed. NFL and Backpressure Rerouting are two modules to reduce or divert traffic when congestion occurs, so that SNGF has available candidates to choose from. The last mile process is provided to support the three communication semantics mentioned before. Delay estimation is the mechanism by which a node determineswhether or not congestion has occurred. And beacon exchange provides geographic location of the neighbors so that SNGF can do geographic based routing.

Figure 4 SPEED Protocol- Image reproduced

SPEED facilitates real-time communication because it provides desired transfer rate over the network. It provides different types of communication services i.e. unicast,multicast and any cast. Stateless Non-deterministic Geographic Forwarding (SNGF) identifies next hop whenever source node transmit the data.

SPEED only stores the information of very next node, so it requires less memory. Neighboring beacon is used for information interchange between nodes. To identify trafficchanges in the network two types of on demand beacons are used i.e. delay estimation and back pressure beacon.

SPEED uses Backpressure rerouting mechanism for congestion controlhandling in the network. Packets are given an alternative route to destination and normally no packets are dropped in Backpressure rerouting mechanism. Only when there is no alternative route to destination and network become very congested than the packets are dropped. It will consume less energy if there is no congestion in the network and also it will save energy by selecting shortest path to the destination but if there is congestion in the network, the energy consumption will be slightly higher. SPEED is a hybrid protocol because it combines the functionality of MAC and network layer to minimize the delay and to provide better response to

congestion. Figure 4 shows the protocol structure of SPEED protocol.

VI - REAL-TIME POWER-AWARE ROUTING IN SENSOR NETWORKS (RPAR)RPAR is a real time protocol proposed in which achieves application-specified communication delays at low energy cost by dynamically adapting transmission power and routing decisions based on packet deadlines. The primary design objective of RPAR is to increase the number of packets which meets their deadlines. Another distinguishing feature of RPAR is that it handles realistic properties of WSN such as lossy links, limited memory, and bandwidth. RPAR has four components: A. Dynamic velocity assignment policyIt uses the velocity assignment policy to map a packet’s deadline to a required velocity.B. Delay estimatorThis evaluates the one-hop delay of each forwarding choice in the neighbor table, i.e. the time a node takes to deliver a packet to neighbor N at power level p.C. Forwarding policyBased on the velocity requirement and the information provided by the delay estimator, It forwards the packet using the most energy efficient forwarding choice in its neighborhood table that meets the required velocity.D. Neighborhood managerThis manager attempts to find a new forwarding choice that meets the required velocity through power adaptation and neighbor discovery, when the forwarding policy cannot find a forwarding choice that meets the required velocity in the neighbor table. RPAR trades-off between the communication delay and throughput. It trades capacity and energy for improving latency by increasing transmission power and when there are loose deadlines, the transmission power is adjusted accordingly. The delay bounds for each packet is provided by the application

VII - MULTIPATH AND MULTIPLE-SP EED(MMSPEED)

MMSPEED is an extension of SPEED protocol[4]. The aim of MMSPEED is to make routing decisions locally on the nodes and also to facilitate differentiated QOS in timeless and reliable domain. To make decisions locally without maintaining end-to-end routes, it uses geographic routing method. It assumes that main identifier for destination is its geographic location rather than node ID. Periodic location update packets are used to instantly update the location information with neighbors, so that every node is aware of its very next neighbor within its range. Each node makes pre-packet decisions depending on the geographic location of the neighbor.

The geographic localized routing mechanism has many advantages over traditional routing approach:i) This approach is suitable for larger networks (scalability).ii) Minimum delay suitable for time-critical applications.iii) Dynamic adoption to network topology changes.

To achieve higher performance, MMSPEED needs MAC layerto support following function:

i) To assign priority for accessing shared-medium dependingupon the speed layer.ii) Reliable packet deliveryiii) Average delay measurementiv) Measurement of loss to individual neighbors

Figure 5 MMSPEED Protocol- ImageTo achieve above MAC layer goals another protocol is profromposed in. MMSPEED establishes redundant path to each destination and also provides multi-speed transmission. Fordifferent speeds different QOS levels can be set to improve performance. MMSPEED and SPEED are different in way that MMSPEED offers different level of QOS according to network and traffic requirements. Figure 5 shows the protocol structure of MMSPEED protocol

VIII - LEACH ProtocolIn the LEACH protocol, random,

adaptive, self-organizing cluster formation method. Figure 6depicts a wireless sensor network protocol based on LEACH is divided into five clusters, each cluster has a black circle represents the first cluster node , the rest of the white circle indicates a non cluster head node. Each cluster has a cluster head node, protocol randomly selecting cluster head node cycle, the energy of the entire network load equally distributed to each sensor node can achieve lower energy consumption, the purpose of improving network lifetime

Figure 6 LEACH protocol cluster structureFrom the above analysis shows that LEACH protocol has the following deficiencies: (1) the use of cluster head nodes in random rotation method which can reduce the

energyconsumption, but repeatedly re-clustering will still consume more energy.(2) different clusters, the cluster head node and cluster head nodes from non-different, the communication process increases the energy consumption of cluster head. (3)The cluster head node need to communicate with the sink node to complete the data fusion work, energy consumption increased.

VIII - Conclusion:Providing an energy-efficient multicast routing protocol isof paramount importance for many new applications beingdeveloped for the resource scarce in WSNThis paper presents an overview of different energy efficientmulticast routing protocols for wireless sensor networks. Generally,all of them needs low processing and memory forrouting that means lower energy requirements.

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