## 2 Literature Survey  
In this section, we present some of the state-of-the-art techniques that we have also used, apart from [17], for the comparison with our proposed technique. Also at the end of this section, a tabular representation of various related techniques is given for ease in comparative analysis thereof. The Multilayer Cluster Designing Algorithm (MCDA) for Lifetime Improvement of wireless sensor networks by [PERSON] _et al._[5] is a hybrid approach in its communication architecture and architectural design perspectives. MCDA uses a multilayer approach comprising a first flat layer in the BS footprint and subsequent clustered layers. The design of former layer is initiated centrally whilst a distributed fashion is applied in the design of the latter. The deployed nodes in the flat layer are termed as first layer nodes. The authors' start the network clustering from the second layer up to the network boundary. The cluster heads in the second layer are selected by the elected decision maker nodes of the first layer. Neighbor Counter, Decision Maker Nodes and Packet Sequence ID with Postfix Counter are the key factors in designing the clusters. Neighbor Counter is used at various steps for selecting one node over others for selection of various roles, _i.e._, decision maker, cluster head, while Decision Maker Nodes are used for selection of cluster heads from the subsequent layer, and Packet Sequence ID with PostfixCounter is a packet id that is used for grouping nodes and for choosing one node over others from that group for becoming a CH. Second layer nodes elect the node with highest node density as their decision maker node. Second layer nodes communicate their nodal density in their turn to their decision maker nodes to take part in the competition for becoming a CH. Time slots are assigned to these nodes based on the Time Division Multiple Access (TDMA) technique. When the first node of the second layer communicates its nodal density to a decision maker node, it assigns a sequence number with postfix counter \"0\" to this packet. All the recipient nodes of the second layer nodes save this packet sequence number and become a part of the same group. All the nodes having packets with the same packet sequence number are included in the same group. Only those nodes of a group communicate their nodal density to decision maker nodes which have highest nodal density than their previous nodes. These nodes increment the postfix counter, that provides a twofold advantage: (i) to let the other member nodes of the same group know about their nodal density; (ii) to let the non-member nodes know that they should neither continue this postfix counting nor should they save any info about other group's member nodes. This postfix counter assists the packet sequence number in separating the members of one group from other. The node right after the last member of first group communicates to its decision maker node and assigns a new packet sequence number with postfix counter \"0\". After collecting the nodal density of the second layer's selected nodes, the decision maker nodes elect the CH having the highest nodal density among the second layer's addressed nodes. The elected cluster heads broadcast \"_Join Request_\" packets. This is to inform other sensor nodes of its availability as a CH. Recipient nodes send their consent message in the form of \"_join accept_\" messages to become the cluster members. If a \"_join Request_\" message is received from more than one CH then the membership decision is based on the current load on the CH, _i.e._, the CH having a smaller number of member nodes is preferred to be attached with it. Another idea by [PERSON] _et al._[16] with the name Threshold Based Load Balancing Protocol for Energy Efficient Routing in WSN (TLPER) exists in the literature. The idea considers nodal density and geographical location of nodes to decide centrally at the BS about the cluster heads and distributed selection of cluster members.