SURVEY ON TECHNIQUES TO EXTEND LIFETIME OF WSN Priyanka Jadhav 1, Prof. N. A. Mhetre 2 1,2

SURVEY ON TECHNIQUES TO EXTEND LIFETIME OF WSN Priyanka Jadhav 1, Prof. N. A. Mhetre 2 1,2 Department of Computer Engineering, Savitribai Phule Pune University, India ABSTRACT: Existing algorithms, protocols, techniques of wired or wireless network cannot be directly applied for the WSN because limited energy, structure of sensor nodes.wsn has wide application in different areas. Sensor nodes consume energy during collecting, processing, transmitting and receiving of data. Energy is the main resources for the WSN node and life of WSN completely depends on energy of sensor nodes. As we know sensor network is made up of a large number of densely deploy sensor nodes. The position of sensor node is not predetermined which allow random deployment inaccessible environment. As compared to Ad-Hoc network, sensor networks are limited in power and computational capacity. So energy consumption is major performance objective in WSN. There are different techniques available for reducing energy consumption to increase lifetime of WSN. Keywords: Wireless Sensor Network (WSN), Connected Dominated Set (CDS), sleep scheduling, Virtual Backbone. [1] INTRODUCTION Wireless sensor networking is a rapidly growing technology having number of applications in medical, robotics, military, etc. This network family form with number of nodes called as sensors. All these nodes are present in a distributed fashion and coordinates with each other to perform task. Generally sensors perform four basic activities- i) sensing unit ii) processing unit iii) transceiver unit iv) power unit. Energy is the main resource of the WSN and the lifetime of a sensor network depends totally on the energy of the sensor nodes. There are different definitions about network lifetime- (i) At least one element zero or die: If the energy level of any element becomes zero then the first node is used to define network lifetime. (ii)total number of active nodes: Higher number of alive nodes used to define longer network lifetime. (iii) The network fails if the fraction of alive, connected dominating set nodes falls below given threshold. [2] RELATED WORK WSN is an Ad-Hoc network with no particular structure. For better routing, in Ad-Hoc network virtual backbones are formed by using Connected Dominating Sets (CDS).Fig.1 shows the representation of CDS. Load balancing is the essential in the CDS because nodes present in CDS have more load of communication.as the number of nodes communicating with each other is more, fast discharge of energy is done. To avoid this need of rotation for selection of 37

Survey On Techniques To Extend Lifetime Of WSN nodes present in CDS [2].A CDS graph persuades a spanning tree graph where nodes of CDS are internal nodes of the spanning tree. From CDS, MCDS (Minimum CDS) problem is formed which is NP-Hard. To avoid early depletion of energy of nodes present in single CDS rest of the nodes present in G where G= (V, E), perform partitioning of G into a number of disjoint CDS, which directly results in lifetime of the network. Switching of CDS to fresh CDS developed Connected Domatic Partition (CDP) problem. Proximity aware cluster partitioning and new distance construction algorithm is developed for avoiding CDP problem. Fig.1.Representation of CDS For designing of MAC protocol for WSN two main characteristics must be considered. (i)scalability: Network size, design is changed with topology. So developed MAC protocol must support all changes of WSN (ii) Topology: As the sensors are battery powered, extend network lifetime becomes a critical issue. The basic task of MAC protocol is to avoid collision. Basically MAC design of WSN divided into two groups-(i) contention based- e.g.dcf (Distributed Co-ordination Function) [7].Energy consumption is more because of idle listening. (ii)tdma listening: which follows reservation and scheduling results in less energy consumption compared to contention based. In TDMA there is also the consideration of the duty cycle, which avoids idle listening. There are some major sources of energy waste: (i) Collision: If any packet discarded within network a network it is retransmitted again. As it is retransmitted it requires more energy. (ii)overhearing: like man in the middle attack,data captured by another node which results data not reach to the desired destination.(iii)control packet overhead: sometimes lower priority data get transmitted again and again results more energy consumption.(iv)idle listening: nodes are in listen mode for receiving some traffic which is actually not send. But if nothing is sensed for a long time the node is in idle mode for a long time. For avoiding this entire energy waste S-MAC concept is proposed [3].S-MAC is a protocol designed which mainly support collision avoidance using three main things: (i) Periodic sleep and listen: If no any data is sensed then node becomes idle for longer time. To avoid this nodes perform periodic sleep mode,i.e. node is in idle mode for certain time amount,it then wakes up to check is anyone wants to send data to it.fig.2 shows a diagrammatic representation of periodic listen and sleep schedule. When nodes at sleep mode radios of sensors are turned off and timer is set for awake.it is not necessary that listen and sleep time are same, but for simplicity we keep it same. To maintain synchronization with 38

neighboring nodes, each node must maintain its schedule table with its known neighbors. For conversation RTS and CTS packet is used which is the same scheme as that of IEEE 802.11 i.e. node who wants to communicate send RTS packet to neighbors and waiting for reply.receivers replies with CTS and transmission of data begin,till complete data transmission they not follows sleep schedule. Fig.2. Representation of listen and sleep schedule (ii)message passing: Message contains the information of useful data or packets. Sometimes it can be long.in case if there is any error during message passing then it needs to be transmitted again fully. The major drawback of long message transmission is that even though there is minor error, and then also need to resend it completely instead of that particular erroneous packet. To avoid this concept of message fragmentation is used.in which whole message gets fragmented divided into small and transmit them in burst, so whenever sender sends fragment it waits for ACK.If it fails to receive ACK.If will retransmit current fragment immediately. (iii) Collision and overhearing avoidance: collision occurs when multiple senders wants to communicate or send to receive at the same time.mac protocols basically designed to avoid collision. There are some WSN applications; where there is a need to deploy sensor nodes over large, unfriendly environment, so in that case it is difficult to replace them again and again. So in that environment, replacing nodes becomes much costly i.e. energy extension issue is at a priority level. Q. Cao et al.[4] suggest the idea of the surveillance delay which is combination of detection delay and packet delivery latency and new protocol connectivity maintenance is developed which basically works for urgent events(like fire).in sleep scheduling there are nodes are at sleep mode for maximum time. To check an activity there is periodic awake, which helps to increase longevity along with increase in message delivery latency because it must wait for next hope awake and ready to receive it. Here is also use of sleep scheduling in such a way that during a finite time interval is referred as detection delay. Two step sleep scheduling algorithm is developed.in first level select primary subset and in second level maintain duty cycle of primary node in such way that minimum average detection delay will find out for that particular area. In the field of WSN some large scale applications require critical monitoring. For such a class node are deployed in such way that immediate notifications received even though the event is rare, for such applications,there is need to develop a design system in such way that, use average power consumption along with guaranteed packet delivery over multiple hops. Some wakes up techniques are available, grouped into two types :( i) scheduled wakeup-in 39

Survey On Techniques To Extend Lifetime Of WSN which time synchronization between nodes assumed.(ii) wake-up on demand-in that data or messages are sent only when nodes get awake. So for rare but urgent event detection new multi-parent scheme evolved for reducing transmission delay and detection delay with use of the synchronous schedule wakeup method [5]. For developing this scheme, there is consideration of worst case delay which mainly present when any node is present far away from the base station. There are some existing wake up patters like S-MAC (Synchronized) in which nodes follow periodic sleep and active cycle, DMAC (staggered patterns) which is a data gathering protocol in which communication pattern is unidirectional, ladder pattern which is not symmetric, so there is difference in forward and backward delay distribution, two ladder pattern more complex but better than ladder pattern, crossed ladder pattern comparatively more complex but more energy efficient. In multi-parent scheme crossed ladder pattern is consider where multiple parents are assigned to route and message passing is from multiple routes. Four basic states of sensor nodes as sleep, idle, receive and transmit. In sleep mode or state radios of sensor node turn off,which helps to prevent extra power consumption. In idle mode, nodes neither receive nor send any data. Energy consumption is mainly done during sensing and communication.some power saving mechanisms are grouped in following categories: (i) Use of alternate sleep and active mode for sensor nodes.(ii) adjust the transmission area (iii)use some data collection and efficient routing schemes (iv)avoid more data transmission. For target coverage problem target sets with known locations are considered. These target sets are formed by dividing available sensor nodes, in such a way that each set cover all target locations [6]. For reducing power consumption of network, only one set is active at a time only, i.e. nodes of that active set are in active mode and others are in sleep mode. To find out the target coverage problem, energy efficiency and connectivity of nodes is to be considered. Maximum set covers (MSC) problem is defined for organizing sensing nodes, which is NP-hard problem [9]. As there are different disjoint sets are available, single or every sensor can be part of more than one set, which allowing the sets to perform operations at different time interval. If there is a decrease in the number of monitoring targets over specific sensing range, then it is helpful to increase in network lifetime. Yaxiong Zhao et al. [1] proposed a new sleep scheduling algorithm named as Virtual Backbone Scheduling (VBS). Multiple backbone formation helps to distribute consumption of energy equal which allows full utilization of available energy to increase the network lifetime. To find out the optimal schedule MLBS problem is considered as NP-hard [9]. For MLBS problem two centralized algorithms are designed: (i) Scheduled transmission graph (STG): used to model a scheduled in WSN. In STG, different states are considered, in which initial states are a starting point of scheduling. There is one to one mapping between states and backbone. Fig.3 represents the STG structure. The energy level of each round has been calculated. If any one element zero, energy level becomes zero if there is a scenario where zero energy levels are less than non zero energy level results in end of network life. In STG sink is added into each backbone. STG gives the longest possible path of the network. To maintain the performance and decreasing the scheduling complexity round length should be increased. 40

Round 0 Round 1 Round 2 Round i {B1,E1} {B1,E1} {B1,E1} {B2,E2} {B2,E2} {B2,E2} Initial {B3,E3} {B3,E3} {B3,E3}......... {Bp,Ep} {Bp,Ep} {Bp,Ep} Backbone transition Fig.3. Representation of STG (ii)virtual scheduling graph (VSG): sensor nodes of original graph are converted into virtual backbones. To find out the schedule on VSG any CDS construction algorithm [2] is used. For construction of multiple virtual backbones first defined virtual node with ɛ. Normally original node is called as ancestor having energy Er that is for each virtual node available energy is [Er/ ɛ]. For the formation of virtual group, all nodes must be from same ancestor only. If in the original graph, two ancestors neighbors then only two virtual groups are neighbor. When energy of all the ancestors decreases, algorithm stops. For the implementation of VBS, iterative local replacement (ILR) method is used to maintain the complexity of the network. New CDS has to form with replacement of nodes and ILR helps to find out that replacement nodes. For implementation of ILR, topology control and energy consumption of sensor nodes are to be considered to avoid costly message exchange of ILR. In simultaneous replacement of all backbone, collision and data loss occurs. Because of these issues there is of more energy consumption and more execution time. So to avoid this new control based scheme is developed which ensure that the replacement of nodes not perform at the same time. Before actual starting of node replacement some threshold value is declared which helps to stop the replacement when energy becomes low. To find out the replacement node rule1, rule2 and rule k consider along with Marking Process [8]. As we know it is important to maintain QoS with improving the network lifetime of WSN. For maximizing the network lifetime, existing STG algorithm [1] creates static virtual backbones. But we know that in STG, if any node becomes dead or fail, then that backbone become invalid. [3] ANALYSIS OF REALATED WORK Table 1: Comparison of various scheduling schemas (--: No comment in respective paper) 41

Survey On Techniques To Extend Lifetime Of WSN [4] PROPOSED WORK Our main aim is to provide QoS with extending WSN lifetime. In STG based VBS algorithm, CDSs are formed prior and then swap them to find out the schedule.but if any sensor node in the backbone is dead or fail due to any reason in STG, then the entire backbone becomes invalid, this degrades the QoS.But in the new proposed scheme we will create backbones dynamically with considering nodes having sufficient energy along with last sense data value should be above declared threshold. Because if we consider only remaining energy then there may be chances that critical location data may not be captured. 1) What is need of threshold value? The threshold value is controlling parameter for the particular application of the system. It may be harmful to the system if sensing parameter goes beyond the threshold. In order to ensure proper functioning and safety of the system we need to maintain that system below threshold value. Sensor nodes are used for this purpose. 2) Why to consider threshold value of energy and sensing parameter? i) To ensure proper functioning of the backbone threshold value of energy must be considered. If energy goes down below a certain level then there are chances of failure of node and it becomes costly then to form a backbone. ii) It may happen that sensor energy level may be above the threshold but sensing parameter value goes below its threshold value. In that case it could be possible to save energy of sensors by neglecting that sensor from current backbone. [5] CONCLUSION Wireless Sensor Networks (WSNs) are keys for various applications that monitor physical or environmental conditions such as temperature, sound, vibration, pressure, motion or pollutants and to cooperatively pass their data through the network to a main location. In these applications, sensor nodes use batteries as an energy source. Therefore, energy efficiency becomes critical. To meet this challenge, there is the development of a new technique called Virtual Backbone Scheduling (VBS). VBS combines virtual backbone and sleep scheduling, which achieves longer lifetimes for WSNs over existing methods. 42

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