# Optimization of Clustering in Wireless Sensor Networks: Techniques and Protocols
## 6 Recent Advancements in Clustering Optimization Algorithms
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Ref** & **Protocol** & \begin{tabular}{c} **Data** \\ **Transmission** \\ \end{tabular} & \begin{tabular}{c} **Cluster** \\ **Topology** \\ \end{tabular} & \
\begin{tabular}{c} **Cluster Size** \\ **Cluster** \\ **Mobility** \\ \end{tabular} &
\begin{tabular}{c} **Deployment** \\ **Role of CH** \\ \end{tabular} \\ \hline
[70] & GATERP & One-Hop & Centralized & Equal & Static & Homogenous & Yes \\
[71] & HACH & One-Hop & Centralized & Unequal & Static & Homogenous & Yes \\
[72] & MRP-ACO & One-Hop & Hybrid & N/A & Static & Heterogeneous & N/A \\
[73] & GADA- & Multi-Hop & Distributed & Equal & Static & Heterogeneous & No \\
[74] & LEACH & Multi-Hop & Distributed & Equal & Static & Heterogeneous & No \\
[75] & ABC-SD & Multi-Hop & Centralized & Unequal & Static & Homogenous & No \\
[76] & ICWAQ & One-Hop & Centralized & Equal & Static & Homogenous & No \\
[77] & Bee-Sensor-C & Multi-Hop & Distributed & Unequal & Static & Homogenous & No \\
[78] & TPSO-CR & Multi-Hop & Centralized & Equal & Static & Homogenous & No \\
[30] & PSO-ECHS & One-Hop & Centralized & Unequal & Mobile & Homogenous & Yes \\
[79] & DFCR & Multi-Hop & Distributed & Equal & Static & Heterogeneous & Yes \\
[80] & DFLBCHSA & Multi-Hop & Distributed & Equal & Static & Homogenous & Yes \\
[81] & MOFCA & Multi-Hop & Distributed & Equal & Static & Homogenous & Yes \\
[82] & FL-EEC/D & Multi-Hop & Distributed & Equal & Static & Homogenous & Yes \\
[83] & DFLC & Multi-Hop & Distributed & N/A & Static & Homogenous & Yes \\
[84] & HSA-PSO & Multi-Hop & Distributed & Unequal & Mobile & N/A & Yes \\
[85] & HABC- & Multi-Hop & Centralized & Unequal & Static & N/A & No \\
[86] & iCSHS & Multi-Hop & Centralized & Unequal & Static & Homogenous & No \\
[87] & hybrid & Multi-Hop & Distributed & Equal & Static & Homogenous & Yes \\
[88] & DGSA & Multi-Hop & Distributed & Equal & Static & Heterogeneous & No \\
[89] & GA-ANFIS & Multi-Hop & Centralized & Equal & Static & Homogenous & Yes \\
[90] & FAMACROW & Multi-Hop & Distributed & Equal & Static & Homogenous & Yes \\
[91] & LEACH-SF & One-Hop & Centralized & Equal & Static & Homogenous & Yes \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Overview of the selected articles. Figure 11: An overview of clustering parameters from the literature. * Method: A clustering scheme can use either a centralized or a distributed method. Task implementation in these methods can be carried out using hybrid, distributed, or centralized mechanisms. The method's clustering phase can be distributed while the routing phase is centralized (either directly by a BS or with the help of a BS). The mechanism adopted across the entire algorithmic process is analyzed using this parameter;
* Data transmission: Some methods use a one-hop direct link between the CH and the SNs, while others rely on multi-hop connections. Multi-hop intra-cluster communication is suited for methods with few CHs and where the nodes are placed far from the CHs, or for methods where the SNs have transfer restrictions. This evaluation criterion considers the parameters as either one-hop or multi-hop;
* Cluster size: Cluster size can be equal or unequal based on the load distribution on the formed clusters. Load inequality among clusters is caused by variation in the distances between the BS and the SNs;
* Mobility: The CHs can be mobile or stationary; the movement of the mobile CHs is limited. The management of the topology of networks with mobile CHs is more tedious than that of those with stationary CHs;
* Deployment: WSN can be categorized into heterogeneous and homogeneous networks based on the resources of the SNs. SNs in the homogenous networks are equal in terms of energy level, computation power, and communication resources; CH selection is performed randomly or based on other criteria. In heterogeneous networks, the capabilities of the SNs are different.