Sensor low cost and implementation is also

Sensor is a digital device that detects or responds to the input given by anyphysical object or any type of environment condition. It can detect any typeof sound, motion, pressure etc. It is widely used in commercial and industrialapplications as to make work more easier. A WSN system incorporates a gatewaythat provides wireless connectivity back to the wired world and distributed nodes.It consists of nodes that processes some information and share or transmitwith other nodes in the network. Each sensor node consists of a radio transceiverwith antenna, a micro controller, electric circuit and a power supply, commonlybattery. Size of node may vary depends on the requirements. Structure of nodesmay contains a few sensor node to hundreds or thousands of them.1.1.2 Topologies of WSNThere are four main topologies of wireless sensor network. Point to point network Star network Tree network Mesh network1.1.3 ApplicationsThere are many applications of WSN. We can use WSN in many areas. Some ofthe examples are given belowHenrique C. Silva, 2016 Used in disaster relief operation in danger areas like volcanoes where tem-perature changes are reported to the Base station and the can alarm thearea before any disaster.1 Area monitoring to detect some motions like in wars to detect the motionof enemy in some range. Mostly used in high security area like in Whitehouse, America. Health care monitoring like to detect the physical state of living beings.Temperature, heartbeat, blood pressure are detected by sensors. Earth Sensing. WSN has many application in this eld. For detecting theair pollution, noise pollution, tracking etc. To alarm the rate of pollutionin a area. For Industrial monitoring these are used for machine health monitoring.data center, data logging and in many other places. They are easily found in our home applications. Like in our refrigerators,water tanks they alarm when water is above the speci c level.There are many other applications of WSN and its continuously growing worldwide. Its easy to implement by spending low cost and implementation is also timesaving.1.1.4 Architecture of WSNWireless Sensor Network follows OSI modelHenrique C. Silva, 2016. In this itshaving 5 layers Physical layer: Its purpose is to provide physical requirements to the systemfor optimum output results. Data Link layer: Due to this layer, nodes are able to send and receive thepackets with each other. This layer also provide error correction which canoccurs during transmission of packets. Network Layer: Network layer provides optimal path to transfer packetsbetween the nodes and base station. Its main aim is to provide optimal andless cost e ective path to the packets. Transport Layer: This layer split packets into segments and transmit it overthe network. It also control data ow, segmentation reassembly, segmenta-tion of data, packet securing etc. Application Layer: This layer provide process to process communication innodes along with trac control and management.These layers works together to produce optimum results.In WSN there are two di erent types of nodes that helps in proper and ecientworking of this whole process. A sensor node, which is a primary node used forprocessing some required data taken from the environment situation and anotheris sink node which gather the data coming from all those sensor nodes.2Figure 1.1: Di erent components of Wireless Sensor Network1.2 CharacteristicsWSN share similar characteristics with wireless networks. These are as below. Medium of communication: Wireless Sensor Network uses wireless mediumto communicate. Application Dependent: Wireless Sensor Networks are application depen-dent as they are designed to collect and analyze the real time data, they areimplemented to perform speci c task as per requirements of application. Hardware Constraints: Wireless Sensor Networks mainly uses battery as asource of energy. Lifetime of sensor directly dependent on the battery’s life.It also have some memory which can be increased or decreased dependenton the requirements. Density: As we deploy sensor for our purpose in some range. Density ofsensor can be few to hundreds or thousands dependent on the situation.1.3 IssuesWSN share similar characteristics with wireless networksShantala Devi Patil,2016. These are as below. Lifetime: Main issue with the wireless sensors is the lifetime. Mainly, sen-sors works on battery. As sensor’s lifetime depends on the batteries, it isquite impossible to replace the battery of sensors. So, lifetime of sensor isa critical issue. Flexible and scalable architecture: Density is the number of nodes deployedin the wireless sensor network. Density is application dependent. Data aggregation: It is the process of gathering data from sensors. Nodesfrom clusters sends the data to the cluster head, cluster head node aggre-gates the replies to a single response which saves