# Enhanced Three Layer Hybrid Clustering Mechanism for Energy Efficient Routing in IoT
## 1 Introduction
Many techniques have been proposed in the past few years to reduce energy consumption for getting longer network lifetime. One of the low energy consumption techniques in WSN is formation of clusters and routing data packets towards sinks via cluster heads. The basic Low Energy Adaptive Clustering Hierarchy (LEACH) protocol [3] is a two layer clustering technique in which Cluster Heads (CHs) are selected randomly after every round. At the beginning of every new round, nodes are assigned random number and the one with higher random value is assigned as CH at that round, giving priority to those nodes which are not selected as CH previously. Many improvements are proposed in the choice method of CH in LEACH protocol such as [4; 5; 6; 7]. Recently, three layer clustering hierarchies are proposed for energy efficient data routing in WSNs, which have longer network lifetime as compared to basic two layer clustering techniques. HHCA protocol [8] is an adaptive three layer clustering protocol. Every node in this protocol firstly sends its location and residual energy information to the sink. The sink selects upper layer heads which are named as Grid Heads (GH). Sensor nodes using fuzzy c-means clustering approach (FCM) [9] join grid, and then exchange control packets with each other for selection of CH using the same distributive procedure as used in LEACH with taking residual energy of sensor nodes into account, too. The three layer approach and combination of centrally selection of upper layer GHs via sink and distributive selection of lower layer CHs via sensor nodes shows better results as compared to fully distributive clustering techniques. The problem remaining in this approach is a waste of excessive amounts of energy in transmitting and receiving control packets after every complete round for assigning role of GH and CH to nodes. In Figure 1, a typical three layer clustering topology in WSN is shown. In this paper, an Enhanced Three Layer Hybrid Clustering Mechanism (ETLHCM) is proposed that tackles, to some extent, the issue of large wasteful operations in previous three layer clustering techniques. Energy Levels (EL) for sensor nodes are designed in this paper to limit the exchange of control packets after every round for CH selection. At the same time, EL also used to balance energy consumption between sensor nodes. Nodes that are selected as upper or lower layer heads change their role back to normal sensor node only when their residual energy drops by at least 1 EL. The proposed mechanism reduces the burden of election and selection of lower layers heads in every round, as well as reduces to a large extent the control packet exchange overhead. By reducing wasteful operations, ETLHCM shows better results in the form of long network lifetime and high number of data packets received by the sink. Details of the proposed mechanism are presented in Section 4. Moreover, we added euclidian distance to the sink as another prioritizing parameter besides the residual energy of sensor node in fuzzification process for selection of GHs via FCM approach. Thus, sensor nodes with higher residual energy and less euclidean distance to the sink have more priority to be selected by sink as GH. This results in reducing backward transmission of data packets from lower layer to upper layer to some extent. The proposed mechanism can be used to increase the efficiency of IoT devices by reducing un necessary communication overhead. The rest of the paper is organized as follows. Some energy efficient routing techniques and algorithms are defined in Section 2. In Section 3 issues of existing recent work in three layer routing algorithms are explained in details. Section 4 explains the proposed mechanism and simulation results are evaluated and compared with recent existing works in Section 5. The conclusion and future work are presented in Section 6.