## 3 Related Works  
The Low-Energy Adaptive Clustering Hierarchy (LEACH) protocol [13; 14; 15; 31; 32] emerged under the hierarchical based approach. The nature of this protocol is to create a cluster-based computation for data aggregation, processing and transmission in order to reduce the energy consumption of sensor nodes. To be precise, the specific reason for the development of LEACH was to overcome the depletion rate of sensor node's energy to some extent. LEACH is more efficient in comparison to other traditional algorithms, such as MTE and direct diffusion. Later, Centralized Low Energy Adaptive Clustering Hierarchy (LEACH-C) was proposed, which is a modified version of the LEACH protocol. In this  
Figure 3: Sub-cluster LEACH conceptual structure.  
protocol, during the initialization of parameters for each round, every sensor node transfers its location and energy level status to the BS [15]. Then the BS evaluates the average energy level of the network and sorts of out nodes that have high energy level that can be selected as CH for next very round. Further, for uniform distribution of the cluster, the LEACH Energy Betweenness (LEACH-EB) model was proposed [31]. It performs well in terms of improving network lifetime and reliability. LEACH-EB uses minimum variance in the calculation of energy betweenness for improving the clustering performance. This helps in balancing the energy consumption for each sensor node in the network. Due to this fact, CH selection is done in a more distributive form; i.e., each cluster has a uniform number of N-CH nodes. This helps the CH node to deplete its energy after a round in the uniform rate; otherwise some CH nodes deplete energy very quickly due to more considered N-CH nodes, and the overall energy levels of the CH and N-CH nodes are balanced. The energy efficiency is enhanced relatively in comparison to LEACH protocol. Furthermore, the LEACH-E protocol uses minimum spanning tree approach for enhancement of the overall network lifetime [32]. LEACH-E performs better than the LEACH protocol. The remaining energy of the CH is key parameter for selection process in LEACH-E. In addition to this, IBLEACH is introduced as another energy efficient protocol [33]. An extra phase is embedded between twp phases, i.e., the pre-stage phase. It is introduced in between the cluster setup phase and the steady phase. This phase tries to reduce the energy consumption notably. Additionally, LEACH-EX was proposed as a modified version of LEACH-E [34]. In this protocol, the authors tried to modify the threshold function to get a better response and prolong the network lifetime to a greater extent. For better performance, the LEACH protocol can be implemented with artificial intelligence techniques. LEACH-GA integrates a genetic algorithm into the LEACH protocol to get more energy efficient protocol [35]. In this protocol, an extra phase called the preparation phase is installed during the execution of the first round. This phase helps the selection of CH nodes in terms of optimal values of each CH probability. Every round, all three phases are executed. After every round, the end optimal value is calculated, which helps in the selection of the CH node for the next round. This is how LEACH-GA minimizes the energy consumption, by optimizing the selection of the CH node from all N-CH nodes each round [36].