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Top1. Introduction
WSN is the recent field which aims to connect the devices based on sensor network. In earlier, the sensor nodes are considered to be static and huge redundant nodes are deployed to attain a desired level of coverage. In WSN the energy hole cannot associate straight to the sink because the sending data limits the energy directly and decreases the lifetime. By transmitting farthest nodes to the nearest nodes from the sink and all the gathered data which is in below has been used near the sink as shown in Figure 1(Javaid, 2017).
In the network the group of nodes stopped working and doesn’t take place in the communication and data sensing is known as a hole. These holes are the obstacles for communication. It has an effect for the performance of the network and identifies the attacked, damaged and unreachable nodes. If there is a hole then the data will be routed with the boundary nodes repeatedly which directs to the premature exhaustion of the energy present at these nodes. This will maximize the hole which is in the network (Zahedi & Parma, 2019) (Yang et al., 2015). Due to the congestion in the network identification of holes ignores the energy consumption additionally. It convinces the service quality and lifetime of network.
The below Figure 2 depicts the hole formation in WSN. The solid round denotes the coverage holes and the dotted round denotes the energy or missing hole formed in the sensor network. The huge amount of energy hole produces the network hole which reduces the network lifetime in WSN. There are some effects of network hole formation.
WSN are organized in an unreceptive environment and remain unattended for a longer period of time. The limitations of such nodes fail to carry out the operations in the network. This kind of nodes fails to perform the allocated function and cannot connect with the other nodes which are assumed to be a destroyed node. In this network faulty type of nodes are formed. A node is assumed to be faulty if it gives the result which turn from the result of neighbor nodes and it yields unusual results (Nayak & Das, 2019) (Ahmed et al., 2011). These nodes are considered as an event which comprises the point of the sensor itself. So a destroyed node stops working and holds the network activities. In other aspects the faulty node takes place the network activity and creates unusual results which are not similar to its neighbor node (Ge et al., 2018).
The sensor nodes are destructing with sensor node formation and takes place either by external entity or network deployment. The causes of node destruction and hole creation are as follows:
Power depletion mainly creates node destruction .In this network every node is originated with the certain amount of power battery which gives energy to carry out the tasks and maintains the communication with the other nodes. It is very tough to recharge nodes with difficulty and high cost once it is deployed in the sensor fields .It is difficult in unreceptive regions namely battle field forests and deserts. In this kind of network the human interventions is discarded and remains unattended for long time. While evaluating the network operation a node is in need of energy. The battery progressively decreases to its network activity and communication. If energy finishes, the nodes does not remains alive in the network at some aspects (Kumar Sahoo et al., 2016) (Antil & Malik, 2014). The more power will be spend during the communication than calculations. In some regions, a group of nodes are sometimes busier in calculation and communication. When the energy level comes to an end the nodes displays the properties of the destroyed nodes. The affected region creates the hole and that will never exist in the network (Debnath & Debbarma, 2019) (Wang et al., 2019).