# Variants of the Low-Energy Adaptive Clustering Hierarchy Protocol: Survey, Issues and Challenges
## 3 Comparative Analysis  
Clustering is one of the most stimulating fields in WSNs due to the exceptional features and nature of WSNs. Routing protocols based on the LEACH protocol can be categorized into two main categories: CH-based and cluster formation-based protocols. The protocols belonging to the CH-based category are more effective than LEACH because selecting the CH is performed in the former in an efficient manner and by using efficient techniques. The LEACH protocol has several limitations in terms of CH selection and cluster formation. This study emphasis on the new taxonomy in classifying LEACH variants, which is based on CH selection and cluster formation methods. These variants were developed to maximize the network lifetime and reduce the consumption of energy. The protocols discussed in this study exhibit better performance than LEACH when considering the selection of CH, the formation of clusters, and the consumption of energy. The discussed routing protocols are summarized in Table 10. In this table, the comparison among these protocols is shortened based on the new proposed categories and subcategories. The meaning of the suggested columns in the table is clarified as follows:  
* **Category, Subcategories, and Protocol:** This column lists the two main categories used in this survey and the subcategories belonging to each one. The set of protocols assigned to each subcategory is also listed with the corresponding reference number for each protocol. * **Research Domain:** This column presents the domain of each protocol. * **Modeling Parameters:** This column lists the main parameters used in each protocol, and each protocol selects CHs or forms clusters based on different parameters. * **Contributions:** This column summarizes the main contribution of each protocol. Table 11 provides a summary of the protocols that are discussed above. This summarization is based on different parameters that affect each protocol to help researchers and developers in future studies. These parameters are residual energy, location, complexity, multi-hop, reliability, and load balancing. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Protocol** & **Strengths** & **Weaknesses** \\ \hline DL–LEACH [101] & Good energy consumption. & \
\begin{tabular}{c} Unsuitable for large networks \\ because of short node lifespan. \\ \end{tabular} \\ \hline ICH–LEACH [102] &
\begin{tabular}{c} Increases the lifetime of a network \\ by using intermediate CH. \\ \end{tabular} & Extra overhead. \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Summary of distance-based cluster formation protocols. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  
Selecting the best node to become a CH is a problem in routing protocols and basically affects the overall performance of the network. The selection of the best node to become a CH affects energy consumption and network lifetime due to the tasks of the CH in aggregating data and sensing them to the BS. Another critical issue in designing routing protocols is cluster formation, which also influences network lifetime. Most LEACH-based protocols were proposed to deal with these problems. As shown in Table 10, the majority of existing CH selection-based protocols select the CH node based on residual energy. Specifically, CogLEACH-C, V-LEACH, I-LEACH, and LEACH-1R employ only the residual energy parameter. EEM-LEACH and EMOD-LEACH use the residual energy parameter and the communication cost, and EHA-LEACH utilizes the energy harvesting capacity parameter. I-LEACH and LEACH-SAGA consider the distance to the BS and residual energy, and LEACH-MAC uses advertisement time and distance. Meanwhile, cluster formation-based protocols use some information for forming clusters and re-clustering. For instance, EE-LEACH uses residual energy for distributing nodes. C-LEACH, O-LEACH, and EZ-LEACH employ the locations of nodes and residual energy to divide the network into regions. DL-LEACH and ICH-LEACH utilize distance to the BS, and CL-LEACH utilizes distance to the BS and residual energy.