## 3 Proposed Solution
### Cluster Head Rotation  
One of the most energy intensive processes in a cluster-based network architecture is cluster head rotation. In this process, the role of being the cluster head is transferred to the most suitable node that has a better selection metric measurement than its competitors. In the homogenous network, each node has the same probability of becoming CH in the first iteration, if the decision metric is a homogenous factor. Let \(i\) be a node in a network, which has the probability \(\rho_{i}=1/\pi^{2}\sigma\) to become the cluster head, where \(\sigma\) is the nodal density T\({}_{n}\)/T\({}_{a}\) where T\({}_{n}\)= total number of nodes in the network and T\({}_{a}\)= total area of the network. In our case, if T\({}_{n}\) = 300 and T\({}_{a}\) = 300 m \(\times\) 300 m = 90,000 m\({}^{2}\) then \(\sigma\) = 300/90,000 = 0.0033 nodes/m\({}^{2}\). Energy depletion, converting the optimality to non-optimality, malfunctions, and entrapment are usually the key causes of CH rotation. To resolve this issue, some algorithms re-initiate the complete clustering process as it was performed the first time, while others randomly select a node among the neighbors of the cluster head and redesign its cluster. Our Energy-efficient Cluster Head Rotation Technique (ECHeaRT) rotates the cluster head designation without disturbing the cluster size and its members. The method for CM nodes to access the CH is also adaptive. It may change from direct hop to multi-hop and _vice versa_. The proposed solution defines a threshold level for the CH energy. In case the minimum number of hops to the BS is considered for the election of cluster head in the cluster head rotation process, then there is maximum possibility that the nodes closest to the base station are elected again and again. Also in a cluster, all the member nodes have almost same hop count to the BS, hence, residual node energy seems to be the most suitable choice as a decision metric for the cluster head in this underlying scenario, so in order to achieve the distinguished energy awareness in cluster head rotation by ECHeaRT, threshold levels for CH energy are exploited in two steps:  
1. Load Balancing Threshold (LBT); balancing the load on CH with the Backup Forwarding Node (BFN) when the energy level reaches almost 50% of the initial energy. This initial energy is noted when a node is designated as CH. 2. Role Transfer Threshold (RTT); transferring the role of being CH from an existing CH to the new CH (previously working as BFN) when the energy level approaches about 20% of the initial energy. This initial energy is noted when the node is designated as CH. A depiction of the process for switching a CH in different roles based on its energy threshold levels is given in Figure 2. On reaching \(E_{c}=E/2\) (_i.e._, the current energy of a node that is equal to half of the initial energy of that node) _i.e._, LBT status, the switching function triggers to change the role of \"CH\" to \"CH with shared load\". A CH Rotation message \(Msg(CHR_{init})\) is initiated from the CH towards CMs to get their energy levels. Since the decision metric for the selection of the next CH is being the highest energy carrying node, on the basis of the collected data the next potential cluster head is decided by the existing CH, _i.e._, termed Backup Forwarding Node, for now until a complete assignment of the role of CH is accomplished. The decision is communicated to the selected node and the acknowledgement is received. The cluster member nodes that receive this acknowledgement directly from the newly decided CH (BFN) send their data packets to it while the other member nodes of the same cluster still keep on communicating their data to the existing cluster head. On reaching \(E_{c}=E_{i}/5\), _i.e._, 20% of the initial energy of the node (RTT level), the existing CH broadcasts a message to its member nodes to communicate the info of \"role transfer to BFN\". In this scenario, two cases exist:  
_Case I_: If all CM nodes have direct access to the CH.