Abstract
Wireless sensor networks have gotten significant attention in recent times due to their applicability in diverse fields. Energy conservation is a major challenge in wireless sensor networks. Apart from energy conservation, monitoring quality of the environmental phenomenon is also considered a major issue. The approaches that addressed both these problems are of great significance. One such approach is node scheduling, which aims to divide the node set into a number of subsets such that each subset can monitor a given set of points known as targets. The chapter proposes a priority coding-based cluster head selection approach as an extension of the energy efficient coverage protocol (EECP). The priority of the nodes is determined on the basis of residual energy (RE), distance (D), noise factor (N), node degree (Nd), and link quality (LQ). The analytical results show that the proposed protocol improves the network performance by reducing the overhead by a factor of 70% and hence reduces the energy consumption by a factor of 70%.
TopMinimizing the energy consumption of the sensor network is a major research challenge. There are various energy efficient approaches proposed in the literature such as energy efficient routing, clustering, data aggregation etc. The energy efficient routing algorithms are basically concerned with the determination of optimal routes along which the energy consumption is least and network performance is enhanced. The clustering approaches aim to divide the set of nodes into a number of clusters such that the similarity within the cluster is usually greater than between the clusters. In each cluster usually a CH is selected which is responsible for the data collection and aggregation on the sensed data by the cluster members. However if a same node is selected as a CH then it will exhaust it’s energy sooner. So dynamic clustering are also considered. The data aggregation based approaches aim to reduce the number of bits required to transmit a data packet. The pioneer clustering approach is considered as Low Energy Adaptive Clustering Hierarchy (LEACH) protocol for the static network Heinzelman (2000). The LEACH protocol operates in rounds and each round is divided into two phases as: setup phase and steady state phase. The setup phase consists of the determination of CHs which will remain constant till the network lifetime. The steady phase consists of sensing and communication functionalities. For the cluster head selection, each node generates a random number between 0 to1 and it is compared with the predefined threshold value in the Equation 1:
Where
pr is the percentage of the CHs,
r is the round number and
CH’ is the number of nodes which are not selected as CHs in the previous
number of rounds. The scalability of the LEACH protocol is low as it considers CH as fixed. There are various variations proposed in the literature as in which aims to enhance the performance of the LEACH protocol Rehman (2019), Mhatre (2004), Ahmed (2013), Deng (2011), Kim (2006), Sarma 2010, Anitha (2013).
The different approaches for clustering has also been considered in the literature such as in authors have proposed region based clustering which aims to divide the target region into number of regions. The CH selection process has also been investigated on the basis of several parameters such as residual energy, distance between the CH and the base station, centrality, node degree, survivability factor etc. Few approaches have also considered the clustering process for heterogeneous nodes such as normal and advanced nodes Singhal (2014), Maurya (2014), Maurya (2014), Maurya (2014).
Key Terms in this Chapter
Node Scheduling Approach: The nodes in the sensor network can exist in either active, idle or sleep state. In the active state node is involved in the collection of the data from the environmental phenomenon. In the idle phase node is only sensing the environment and performs no communication operation. In the sleep state the node is not performing any operation. It has been observed that the sensor nodes consume least energy in sleep state. So the redundant nodes in terms of coverage may be put into sleep state such that energy consumption is reduced and network lifetime is maximized. The objective of node scheduling approach is to divide the set of nodes into a number of subsets such that it subset can provide coverage to the specified set of points. The set covers thus obtained are activated periodically by the base station. The network lifetime is such case is proportional to the number of set covers obtained. The higher the number of set covers higher will be the network lifetime.
Energy Efficient: The energy efficiency is usually determined as the difference between the initial energy of the network and energy consumed during the operation of the network. The approaches which minimize the energy consumption in the network are said to be energy efficient. There are various approaches which provide energy efficiency to the sensor network such as clustering approaches, routing protocols etc.
Trust: Trust is a quality of service parameter which reflects the trust worthiness of the nodes. If the trust value of a node is higher, then the node is assumed to provide the desired functionality correctly. If a node shows misbehavior in communicating with peer nodes such as dropping packets or misrouting the data packets then the node trust worthiness is lower.
Quality of Service: Quality of service represents the quality of the functionalities provided by the sensor network. It may be represented in terms of coverage, delay, throughput, reliability and energy efficiency.
Encoding: Encoding is a process of transforming the information into a format which requires less number of bits to represent it.
Network Lifetime: The network lifetime of the network is defined as the duration in which the network can perform the desired functionality. Network lifetime may be defined in different ways depending on the application such as in the clustering approaches the network lifetime is defined as the time when all the nodes in the network dies. In area coverage problem it is defined as the duration till the complete target region is monitored by at least one sensor node. In the target coverage problem the network lifetime is defined as the time duration till all the specified set of targets/points is monitored by at least one sensor node.
Wireless Sensor Network: Wireless sensor network is defined as autonomous network which consists of a number of sensor nodes and a central node known as Base Station. The sensor network main function is providing the observation capability to the network. The nodes in the network are usually battery powered and it is not easily feasible to recharge or replace the battery. The nodes are responsible for collecting the information from the environment and transfer it to the central node for further processing. The communication in the node is usually done in either single or multi hop fashion.
Coverage: Coverage is considered as a quality of service parameter which determines how well and for how long the region of interest can be monitored by the sensor nodes. A region of interest is said to be monitored by a sensor node if it is within the sensing range of at least one sensor node. Depending on the number of nodes which can monitor a given point in the target region coverage is defined as 1-coverage, 2-coverage and k coverage. Mission critical applications may require higher degree of coverage. Coverage is categorized as three types: area coverage which intends to cover entire target region. Target/ Point coverage approaches aim to monitor a specific set of points. The barrier coverage problems are basically used in identifying the penetration points within the target region and are classified as Maximum Breach Path and Maximum Support Path.
Clustering: Clustering is the process of process of dividing the sensor nodes into a number of clusters such that intra cluster similarity is higher and inter cluster is lower. There are various parameters such as residual energy, distance from the base station and node degree etc. to choose the cluster head. Clustering approaches are of great significance from the energy efficiency perspective. The major task of the cluster head is to perform the data collection from the cluster members and transfer it to the base station after performing data aggregation. Aggregation is usually done to reduce the data packets by performing certain operations such as minimum, maximum, average etc.