# Variants of the Low-Energy Adaptive Clustering Hierarchy Protocol: Survey, Issues and Challenges
## 4 Future Issues  
CH selection and cluster formation in WSNs are major challenges due to the important role of CHs in gathering and sending data to the BS. All routing protocols based on LEACH concentrate on maximizing network lifetime and minimizing energy consumption. To accomplish these goals, different techniques have been proposed to enhance the LEACH protocol. The comparative analysis and discussions indicate that several aspects of LEACH must be considered by researchers when \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **This Survey** & \multicolumn{4}{c}{**Related Work**} \\ \cline{3-5}  & & [30] & [31] & [32] & [33] \\ \hline Criteria-based taxonomy & \(\surd\) & \(\surd\) & \(\times\) & \(\times\) & \(\times\) \\ \hline Detailed presentation of & \(\surd\) & \(\surd\) & \(\times\) & \(\times\) & \(\times\) \\ \hline Detailed classification & \(\surd\) & \(\times\) & \(\times\) & \(\times\) & \(\times\) \\ \hline \multirow{4}{*}{Scope of the survey} & CH selection & \multirow{2}{*}{\begin{tabular}{c} Single-hop and \\ multi-hop \\ protocols \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} General review of \\ LEACH \\ protocols \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} General review of \\ LEACH variants \\ and other \\ protocols \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} General review of \\ learning \\ and other \\ hierarchical \\ protocols \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} General review of \\ learning \\ and other \\ heterach \\ protocols \\ \end{tabular} } \\ \hline Qualitative comparison & \multirow{2}{*}{\(\surd\)} & \multirow{2}{*}{\(\times\)} & \multirow{2}{*}{\(\times\)} & \multirow{2}{*}{\(\times\)} & \multirow{2}{*}{\(\times\)} \\ among protocols & & & & \\ \hline Comparison with & \multirow{2}{*}{\(\surd\)} & \multirow{2}{*}{\(\times\)} & \multirow{2}{*}{\(\times\)} & \multirow{2}{*}{\(\times\)} & \multirow{2}{*}{\(\times\)} \\ previous surveys & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Comparison of this survey with existing surveys. designing enhanced CH selection or cluster formation methods. The future issues in designing these methods are as follows:  
* _Complexity:_ Complexity is important in designing protocols, and it directly affects the overall performance of protocols, especially in WSNs, due to the nature of sensor nodes (small memory and small computation capability). Therefore, designing a CH selection protocol with low complexity is important. * _Number of Rounds_: LEACH involves several rounds, and each round consists of processes (e.g., forming clusters, selecting CHs, and data transmission). The number of rounds is a significant factor in routing protocols because it affects the performance of the network. Hence, designing CH selection routing protocols that consider the number of rounds will improve network lifetime. * _Scalability:_ LEACH suffers from communication problems, especially in large-scale networks, due to the direct communication from a CH to the BS. This problem directly affects network lifetime because CHs die early in large-scale networks. To deal with this problem, multi-hop protocols with the capability to find the optimal and shortest path are recommended. * _Security:_ Security problems are major challenges in LEACH and its variants. The CH is the main target of hackers due to its importance in gathering and sending data. Thus, the CH should apply encryption and authentication algorithms to avoid attacks. The problem here is designing a suitable encryption algorithm for sensor nodes that have a small memory and computation capability to minimize message overheads and reduce energy consumption according to the calculations in encryption algorithms. * _Fault tolerance:_ In WSNs, sensor nodes are deployed in a large area and not accessible by humans. Fault tolerance exerts a significant impact on the lifetime of the network. Therefore, efficient algorithms that deal with faults must be designed, especially if the fault is in cluster head.