Analysis of Energy Efficient Routing Protocols in Wireless Sensor Networks G. Beni (Assistant Professor) Department of Information Technology, C.S.I Institute of Technology, Thovalai, Tamil Nadu, India. gsbeni@yahoo.co.in Dr. C. Seldev Christopher (Professor) Department of Computer Science and Engineering St. Xaviers Catholic College of Engineering, Chunkankadai, Tamil Nadu, India. cseldev@gmail.com Abstract In WSNs, the energy of the nodes is usually limited, which has to be consumed economically in order to prolong the lifetime of the network. Due to the energy-constrained nature of these wireless sensor networks the traditional routing protocols cannot be directly applied to WSNs. The objective of this research is channeled towards energy efficient routing and to achieve better quality of service (QoS) provisions. This paper analyses the various routing protocols and their energy efficiency in constrained WSN environment. Keywords WSNs, Routing, QoS, Energy efficiency I. INTRODUCTION A wireless sensor network is a collection of nodes connected together in which each node consists of processing capability, memory, communication resources, sensors and actuators and power source. The functionalities of wireless sensor network include sensing activities, exchanging sensed information, aggregating data, reasoning in a local or distributed manner, raising alarms, activating other sensors, etc. Sensing, processing and communication are three key elements whose combination in one tiny device gives rise to a vast number of remote sensing applications, including environmental monitoring, precision agriculture, medical applications and battlefield surveillance. II. ROUTING ISSUES IN WSNS Routing in wireless sensor networks differs from traditional routing in fixed networks in many ways. Since there is no infrastructure, links between nodes are unreliable, sensor nodes may stop working, and routing protocols have to optimize the energy saving usage. Generally, routing in WSNs can be divided into location-based routing, flat-based routing and hierarchicalbased routing depending on the structure of network. In location-based routing, sensor nodes positions are exploited to route data in the network. All nodes are typically assigned functionality or roles in flat-based routing. But in hierarchical-based routing nodes will play different roles in the network. A protocol is said to be adaptive routing protocol if certain system parameters are controllable in order to adapt to the existing condition of the network and available energy levels. Moreover these routing protocols can be classified into query-based, negotiation-based, multipath-based, QoS-based, or coherent-based routing depending on the operation of the protocol. Besides the above protocols, routing protocols can be further classified into three categories, namely reactive, proactive and hybrid protocols depending on how the source identifies a route to the destination. In reactive protocols, the routes are computed based on demand while in proactive protocols, all routes are computed before they are really in need. The combination of these two ideas is used in Hybrid protocols. It is preferable to employ table driven routing protocols when sensor nodes are static. It is observed that a significant amount of energy is consumed in route identification and setup of reactive protocols. Another category 3029
of routing protocols is known as the cooperative routing protocols in which nodes send data to a central node where data can be aggregated and subjected to further processing, hence route cost in terms of energy usage is reduced. III. ROUTING PROTOCOLS IN ENERGY AWARE WSNS Conventional routing techniques cannot be applied to wireless sensor networks since there is no fixed infrastructure, failure of nodes, unreliability of the links. Various routing algorithms were developed for wireless networks and all major routing protocols proposed for WSNs may be classified into five categories as shown in Table 1. Table 1: Routing Protocols for WSNs Category Representative Protocols Location-based Protocols Data-centric Protocols GAF, GEAR, GeRaF SPIN, Directed Diffusion, Rumor Routing, COUGAR, ACQUIRE Hierarchical Protocols LEACH, PEGASIS, HEED, TEEN, APTEEN Mobility-based Protocols QoS-based protocols SEAD, TTDD, Joint Mobility and Routing SAR, SPEED, Energy-aware routing A. Hierarchical Routing In hierarchical routing the network consists of several clusters of sensors and each cluster has a Cluster Head (CH) which is responsible for controlling all the activities of all sensors in its cluster. The advantages of Hierarchical routing protocols are extra scalability, less energy consumption, less load, and more robustness. The hierarchical routing approach groups the sensor network into clusters and all exchange of information are made between the cluster heads as shown in Fig 1. Data moves from the lower layers of the protocol to the higher layers enabling to cover larger distances. Fig 1: Cluster-based Hierarchical Model B. LEACH Low-energy adaptive clustering hierarchy (LEACH) is one among the energy-efficient hierarchical clustering protocol introduced for reducing power consumption and prolonging network lifetime by randomly selecting Cluster Heads (CH) among the various clusters where the routing information is passed only through the cluster heads which reduces the amount of energy consumed by the nodes. Clusters are formed by localized coordination which restricts the amount of data send to the sink and also makes the routing robust and scalable. Also LEACH uses fusion technique which aggregates the data and conveys only useful 3030
information to all the nodes. The responsibilities of cluster heads are switched among all the nodes in the cluster in order to evade energy depletion of individual nodes. LEACH works in two phases namely, (i) Setup phase: This phase deals with formation of cluster, advertising Cluster heads and creation of transmission schedule. (ii) State phase: This phase deals with data fusion, data compression and transmission of data to the sink. This is a distributed protocol that requires no prior knowledge of the network and uses single hop routing technique from the source node to the cluster head and from the cluster head to the sink node. If the source is farther away from the sink the cluster heads needs to spend enormous energy and extra overhead is introduced in the network due to dynamic clustering. C. PEGASIS PEGASIS is Power-Efficient Gathering in Sensor Information Systems which is an extension of LEACH which forms a sequence of sensor nodes that gathers data and sends the data from the nodes to the sink as a cluster. In this protocol the Global knowledge of the network is mandatory and the sensor node chain is constructed in a greedy way. Suppose if a node fails the chain is reassembled from remaining nodes bypassing the failed node. Each sensor from the chain sends the aggregated data to the sink during each round. Also it is observed that the lifetime of sensor nodes in PEGASIS is twice that of LEACH. Since a sensor node should have knowledge about the energy status of its neighbors in order to know where to route its data it requires dynamic topology adjustment. Such topology adjustment may introduce considerable overhead especially for highly utilized networks. D. HEED Hybrid Energy-Efficient Distributed Clustering is too an extension of LEACH and uses energy consumption in a distributed manner, terminates clustering in fixed number of iterations, extends the lifetime of network, reduces control overhead, produces compact clusters and well distributed CHs. Also it takes into account the degree of the node and uses residual energy as a metric for cluster selection to achieve power balancing. Moreover in inter-clustering communication it uses an adaptive transmission power. It selects CHs at regular intervals based on the combination of two clustering parameters (i) the residual energy of each sensor node which is used to probabilistically select an initial set of CHs (ii) the intra-cluster communication cost as a function of cluster density (i.e. number of neighbors). The HEED protocol improves network lifetime over LEACH clustering since LEACH randomly selects CHs which makes some nodes lose their entire energy and become dead. Since the final CHs selected in HEED are uniformly distributed across the network and the communication cost is reduced. Although, the cluster selection deals with only a subset of parameters, there is a probability to impose constraints on the system. Hence these methods are most suited for prolonging the network lifetime but not meeting out the entire needs of WSN. E. TEEN TEEN known as Threshold Sensitive Energy Efficient Sensor Network Protocol is a hierarchical clustering protocol, which also groups sensors into clusters with each group led by a CH. The sensors within a cluster communicate their sensed data to their CH. After receiving the data from sensors, the CH sends aggregated data to a CH in the higher level until the data reaches the sink. Therefore, the network architecture in TEEN is based on a hierarchical grouping where closer sensor nodes form clusters and this process continues until the BS (sink) is reached in the second level. TEEN protocol is useful for applications where the users can manage a trade-off between energy efficiency, data accuracy, and response time effectively. TEEN utilizes a datacentric method with hierarchical approach for implementation. The vital features of TEEN protocol include its aptness for time critical sensing applications. Moreover, since transmission of message consumes more energy than data sensing, the energy consumption in this format is less than the proactive networks. On the other hand, TEEN is not an appropriate protocol for sensing applications where periodic reports are required because the user possibly will not get any data if the thresholds are not reached. F. APTEEN Adaptive Periodic Threshold Sensitive Energy Efficient Sensor Network Protocol (APTEEN) aims in periodic data transmission and responding to time critical events. Also it is a type of hybrid routing protocol with the aim of allowing the sensor to send their sensed data in regular periods and respond to any sudden change in the value of the sensed information by reporting the corresponding values to their CHs. It supports three different query types namely 3031
(i) (ii) (iii) historical query, which analyzes past data values, one-time query, which takes a snapshot view of the network and persistent queries, which monitors an event over a period of time. IV. ANALYSIS AND DISCUSSION Protocol Name Energy Efficiency Cluster Stability Scalability Delivery Delay LEACH Moderate moderate Very low Very small PEGASIS Low Low Very low Very large HEED Moderate High Moderate Moderate TEEN Very High High Low Small APTEEN Moderate Very low Low Small The study on the various hierarchical protocols has shown different values for routing parameters like energy efficiency, Cluster stability, Scalability and Delivery delay. Above all LEACH has shown moderate energy efficiency and cluster stability and the delivery delay is also very small. Hence LEACH protocol can be employed in applications that require very small deliverydelay and energy efficiency is a constraint.. V. CONCLUSION One of the vital challenges in the design of routing protocols for Wireless Sensor Networks is energy efficiency due to the limited energy resources of sensors. The ultimate objective behind the design is to extend the network lifetime and thereby keeping the sensors alive as long as possible. The energy utilization of the sensors is dominated by data reception and transmission. Therefore, routing protocols that are designed for WSNs should be as energy efficient as possible to extend the lifetime of individual sensors, and consequently the network lifetime. In this paper, we have surveyed few hierarchical routing protocols for a Wireless Sensor Network by taking into account the energy efficiency, cluster stability, scalability and delivery delay. The selection of protocol for a sensor network is a balance between the energy efficiency and communication topology for a typical network and the application where it is used. References [1] S.K. Singh, M.P. Singh, and D.K. Singh, A survey of Energy-Efficient Hierarchical Cluster-based Routing in Wireless Sensor Networks, International Journal of Advanced Networking and Application (IJANA), Sept. Oct. 2010, vol. 02, issue 02, pp. 570 580. [2] Ming Liu, Jiannong Cao, Guihai Chen, and Xiaomin Wang, An Energy-Aware Routing Protocol in Wireless Sensor Networks, Sensors 2009, vol. 9, pp. 445-462. [3] Luis Javier García Villalba, Ana Lucila Sandoval Orozco, Alicia Triviño Cabrera, and Cláudia Jacy Barenco Abbas, Routing Protocol in Wireless Sensor Networks, Sensors 2009, vol. 9, pp. 8399-8421. [4] K. Akkaya and M. Younis, An Energy-Aware QoS Routing Protocol for Wireless Sensor Networks, in the Proceedings of the IEEE Workshop on Mobile and Wireless Networks (MWN 2003), Providence,Rhode Island, May 2003. [5] Jamal Al-Karaki, and Ahmed E. Kamal, Routing Techniques in Wireless Sensor Networks: A Survey, IEEE Communications Magazine, vol 11, no. 6, Dec. 2004, pp. 6-28. [6] W.R. Heinzelman, A. Chandrakasan, and H. Balakrishnan, Energy-efficient Communication Protocol for Wireless Microsensor Networks, in IEEE Computer Society Proceedings of the Thirty Third Hawaii International Conference on System Sciences (HICSS '00), Washington, DC, USA, Jan. 2000, vol. 8, pp. 8020. [7] W.R. Heinzelman, A. Chandrakasan, and H. Balakrishnan, An Application-Specific Protocol Architecture for Wireless Microsensor Networks in IEEE Tmnsactions on Wireless Communications (October 2002), vol. 1(4), pp. 660-670. [8] S. Lindsey and C.S. Raghavendra, PEGASIS: Power-efficient Gathering in Sensor Information System, Proceedings IEEE Aerospace Conference, vol. 3, Big Sky, MT, Mar. 2002, pp. 1125-1130. [9] Ossama Younis and Sonia Fahmy, Distributed Clustering in Ad-hoc Sensor Networks: A Hybrid, Energy-efficient Approach, September 2002. 3032
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