## 2 Related Literature  
Cluster-based routing protocol design has fascinated many researchers, and extensive research articles on hierarchical routing strategies for WSNs are available. Low-Energy Adaptive Clustering Hierarchy (LEACH) [16,17] is a famous and the most cited cluster-based protocol and is addressed as a legacy routing protocol in the field of WSNs. LEACH has given a great way of selecting CHs. However, LEACH suffers from several drawbacks, such as the selection of Cluster Heads (CH) among the set of nodes that may not have sufficient residual energy, the possible selection of CHs in close proximity, or even the possibility that no CH is selected. Such issues of LEACH protocol create instability in the network, and nodes may die out quickly. In this section, we will present recent advancements made in LEACH and other cluster-based protocols. [PERSON] et al. in [18] proposed an improvement to the LEACH protocol termed as LEACH based on Three layers (LEACH-T). The authors have identified that LEACH indulges in long-distance data transmissions. The distance between CHs and sink could be reduced by introducing three-layer CH selection policies. According to these authors, CHs at the second layer select third-layer CH nodes near the sink, thereby decreasing the long-range data transmissions and ultimately conserving the energy of the network. Energy-influenced probability-based LEACH (EiP-LEACH) [19] is yet another protocol based on LEACH proposed by [PERSON] et al. In this method, authors have introduced energy-influenced probability-based CH selection scheme for basic LEACH protocol. EiP-LEACH takes into account the energy parameter while selecting CH nodes. The proposed method helps prolong the network lifetime. For the past several years, the LEACH protocol has been improved based on several parameters leading to better network energy utilization. Such variants of LEACH protocols are reviewed in [20]. Similarly to improvements on LEACH protocol, researchers have also contributed to a variety of clustering methods for WSNs. Based on the type of network topology and node deployment strategies, the network's energy consumption pattern varies. [PERSON] et al. in [21] have proposed a Fan-Shaped clustering technique for large scale sensor network. Authors have given better CH selection methods, solutions to hot spot problems, etc., resulting in benefits such as reduced signaling cost, optimized intra-communication cost, etc. Another cluster-based routing protocol called the Distance-and-Energy Aware Routing with Energy Reservation (DEAER) is proposed in [22]. The DEARE protocol selects high-energy nodes as CHs that are close to the sink. DEARE also avoids energy shortage events at CH nodes by selecting the \"enabler\" nodes as CH nodes. While routing the data from CH nodes to the sink usually involves multi-hop transmissions, an inappropriate relay node selection could lead to inefficient energy consumption in the network. [PERSON] et al. have identified such a problem and proposed a novel energy-aware hierarchical cluster-based (NEAHC) routing protocol in [23]. Their proposed work's main motto is to control the total energy consumption and ensuring optimal energy consumption between nodes. The nature of applications in WSNs also affects the performance and poses new challenges. One such application of WSNs can be found in Underwater Smart things. [PERSON] et al. in [24] have proposed Energy-Efficient Chain-based Routing Protocol for underwater wireless sensor networks (E-CBCCP). Here, to ensure the uniform load on all nodes, authors have suggested a strategy to rotate the role of cluster coordinators, CH nodes, and relay nodes in an energy-efficient manner. Apart from conventional clustering methods, a few authors have preferred to use fuzzy-based procedures for selecting CH nodes. [PERSON] and [PERSON] in [25] have proposed a fuzzy logic-based clustering algorithm for WSN to extend the network lifetime. Authors emphasized the need for additional CH nodes called Super Cluster Head (SCH).