*3.2.1 LEACH – (low energy adaptive clustering hierarchy)*

LEACH is introduced as the first hierarchical routing protocol that uses TDMA (Time Division Multiple Access) to implement the energy efficient routing process in the WSN. The LEACH protocol enables a clustering mechanism that forms a set of nodes based on received signal strength. This set of nodes is also referred to as a cluster, where each node of the clusters is devoted towards the extra opportunistic node called as Cluster-Head (CH). The CH acts as a local data center for all the clusters and uses TDMA and CDMA scheduling to transmit aggregated data to the base station (BS) without intra-frame and inter-frame cluster collisions [13–15].

	- Clustering based Protocol
	- Self-orienting cluster configuration
	- Adaptive and randomized cluster configuration
	- Localized controls for cluster organization and data transfer operations
	- Low-power data access
	- Data aggregation
	- Local compression to minimize overall communication

The operation involved in LEACH protocol is segregated into rounds where each round contains two phases to perform cluster-formation, CH formation, and data transmission in power efficient way.

The following are the two phases which is involved in the LEACH operation.

	- i. Setup Phase

This is the initial phase of the LEACH protocol, in this phase, a grouping of nodes and CHs are formed. The nodes are organized themselves into different groups and these groups with its member nodes is termed as clusters. Initially, each node in the cluster chooses itself to become a CH with a certain probability, and as a CH node, it must contain higher energy than a non-CH node. In the LEACH protocol, the CH selection mechanism is constructed in such a way that CH can randomly change over time to balance the energy dissipation of the nodes and thereby cluster nodes gets an opportunity to become CH in next cycle.

• Formation of CH- The nodes in the cluster uses a random function to choose a number between 0 and 1. If the number found to be less than subsequent threshold value ν(x), then the node becomes the CH of the current cycle.

$$\nu(\mathfrak{x}) = \begin{cases} \theta/\mathbf{1} - \theta \* (r \bmod \mathbf{1}/\theta) : f \mathbf{x} \in Y \\ \\ \mathbf{0} : \mathbf{Otherwise} \end{cases} \tag{2}$$

The above Eq. (2) demonstrates the computation of threshold value, where r is the number of cycle that has completed, x indicates the overall nodes in the network, θ indicates the percentage of the CH, and Y is the non-CH node. Here in this, each node can generate a random number between 0 and 1 and the node becomes CH when its number is found to be less than ν(ϰ), otherwise it will not become CH. Once the CH is selected using the Eq. (2), the CHs-node uses a non-aggressive Carrier-Sense-Multiple-Access (CSMA)-transmission protocol to broadcast the notification message to inform all the other nodes which have played a role for selecting CH in the current cycle. Now based on received signal strength (RSS) of the broadcast notification message, all the non-CH nodes identify that which cluster it belongs to. After each node verified to which cluster it belongs to, then the nodes must have notified to CH that it is a member of its cluster. Therefore the CH plays a role of local data-center to control the transmission of the data packets in its cluster. The CH then initiates TDMA to construct the schedule, then forwards this schedule to all nodes presented in the cluster to ensure that there are no conflicts between data and message transmissions. In order to save power, it also allows each node to put their radio components in a sleep mode outside of their data transmission job. Therefore, the setup phase is complete when all nodes in the cluster are aware of the TDMA schedule, and the steady phase begins.

#### ii. Steady-State Phase

In this phase, the data transmission operation is executed in different frames. In this frame, the cluster node forwards its data to the CH node according to its transmission schedule. In order to preserve energy, each cluster node uses less power dissipation mechanism based on the RSS value of the CH broadcast notification message. Afterward, the CH receives all data from the cluster nodes and then performs the data aggregation operation and transmits resultant data to the sink node (**Figure 3**).

• Analysis of energy consumption in LEACH

The LEACH protocol considers that cluster nodes start with the same energy and the likelihood function with threshold value v(x) not recognizes the remaining power of each node. Therefore, the LEACH gets good reduction rate in energy utilization comparing to direct communication process and MTE routing protocols. However, LEACH distributes the similar-level power-loads to all nodes of clusters, and this will further result in an imbalance of node after running for a long time. Also, if a node with less energy is selected as the CH, the node may quickly drain its energy. If this happens then, the CH will terminate and lose their connectivity to all nodes belonging to its cluster.

The following are the assumptions for Radio Energy Model (REM)

• It also considers that all nodes are aware of their location.

<sup>Ε</sup>*T*ð Þ¼ *<sup>κ</sup>*, *<sup>∂</sup>*

(

dividing power utilization in data aggregation by fx∂2 and amp∂4.

*3.2.2 PEGASIS – (power-efficient gathering in sensor information systems)*

deployed outside from the sensing field.

*Energy Saving Hierarchical Routing Protocol in WSN DOI: http://dx.doi.org/10.5772/intechopen.93595*

supply.

Eq. (4).

process.

**Figure 4.** *Energy radio model.*

**161**

• The REM considers sensor nodes and Sink are all stationary and Sink node is

• All sensor nodes are considered as homogeneous that have the same energy

**Figure 4** displays the first order radio model that considers most of the energy

is consumed in the communication operation performed by the sensor nodes. Therefore, it demonstrates that the energy needed to forward kbits-packets is computed by Eq. (3) and energy utilized in packet reception can be computed by

The LEACH protocol uses radio energy model for power dissipation in the communication process. The numerical Eqs. (3) and (4) is demonstrated below to compute energy utilization in transmission and energy utilized in the receiving

*<sup>κ</sup>*Ε*power* <sup>þ</sup> *κεfs∂*<sup>2</sup>

The above Eqs. (3) and (4) illustrates the energy dissipation rate in the communication process of sensor nodes. The ETx(k,∂) is the transmission energy needed for (kbits-packets) over ∂ distance and Epower is the electric power utilized per bit to run the communication module such as transmission circuit and receiver circuit based on modulation and digital coding. fx∂2 and amp∂4 is the amplification power which is based on the significant rate of bit-error. The ∂0 is the square root of

PEGASIS is introduced as an enhanced version of the hierarchical routing protocol over the LEACH. The PEGASIS protocol follows a chain-based approach where all sensor nodes formulate a chain system, and one leader node is selected randomly to execute data transmission process to sink node. In this, the collected

*<sup>κ</sup>*Ε*power* <sup>þ</sup> *κεamp∂*4, *<sup>∂</sup>*<*∂*<sup>0</sup>

, *∂*<*∂*<sup>0</sup>

Ε*R*ð Þ¼ *κ κ*Ε*power* (4)

(3)

**Figure 3.** *Clustering mechanisms in LEACH protocol.*

	- i. LEACH protocol uses a clustering mechanism which enables less communication load between sensors and Sink.
	- ii. The CH performs data aggregation which leads to minimizing the redundancy factor and saves energy.
	- iii. In this CH uses a scheduling process that allows member nodes to enter into sleep mode. This avoids collision factor and preserves the extra energy consumption.
	- iv. LEACH protocol also allows each sensor node in the cluster to become the CH.
	- v. Random rotation of CH also enhances network lifetime.
	- vi. It also saves energy by following a single hop routing process from the sensor to CH.
	- vii. LEACH does not require the location of the nodes to establish as CH.
	- viii. LEACH is independent and distributed which does not require control information from the sink node.
		- ix. LEACH protocol has one of the big disadvantages is this that if anyhow CH dies then the cluster nodes will become useless their collected data will not reach to the sink node.
