# Clustering for Lifetime Enhancement in Wireless Sensor Networks
## 2 Related Work  
Clustering is the main approach used to enhance WSN performance. It begins with the LEACH protocol [11], which is still considered the foundation of many routing protocols, especially those focused on extending network lifespan. LEACH organizes the WSN into multiple clusters, each composed of several nodes that connect directly to one another. It employs a random-based CH selection process. CHs define their neighbors within a range of 20 m. These neighbors then send the data they collect directly to their CHs. Afterward, the CHs aggregate the data and send them in a single hop towards the BS. This section aims to present the most recent and high-quality work on cluster-based and LEACH successor protocols. In 2021, another study presented an improved version of the LEACH protocol [12]. This protocol aims to extend the WSN's lifetime by considering the clusters' density. They consider that clusters of different densities unbalance the workload of cluster leaders, leading to exhaustion of their energy. They reduce the number of nodes by minimizing the scope of cluster leader selection in dense areas. CHs are selected based on their equivalent densities and residual energy. In addition, the data collected can be sent in one or more hops, depending on what is optimal. To avoid the hotspot problem, the authors of reference [13] focus on selecting nodes close to the base station with a high energy level. They proposed the fuzzy-based EE-LEACH protocol. EE-LEACH uses the nodes' residual energy, density, and distance from the base station to rank them. The best-ranked nodes are then used as CHs. In this way, they ensure that nearby nodes with a large amount of energy are selected and that nodes with less energy are neighbors and remain alive for their lifetime. Random selection of CHs could give nodes with difficult conditions the opportunity to be CHs. To solve this problem, the authors of [14] proposed an energy-aware CH selection algorithm. They take into account the residual energy, position, and centrality of the nodes. They adjust the range according to the dense areas of the nodes, where the clusters can be very dense to obtain fair cluster densities without affecting the connectivity of the nodes. Extending the lifetime and conserving energy in WSNs is a major research challenge due to the small, non-replaceable batteries of the sensors. In [15], the NM-LEACH protocol is introduced to prolong the lifespan of sensor nodes. It considers nodes' residual energy and their distance to the BS. This protocol also improves network stability. It selects an even distribution of CHs by choosing nodes with greater residual energy and shorter distances to the BS. In 2021, [PERSON] and [PERSON] focus on node centrality [16]. They developed a distance-based adaptive low-energy clustering method. It elects adaptive CHs with the lowest possible centrality. In this way, the distance between nodes in the same cluster must be smaller, which reduces energy consumption. They also take into account residual energy, which indicates whether a node is capable of being a CH or of conserving its energy and does not affect the lifetime of the WSN. The limited energy of wireless sensors is always a major challenge. IoT networks suffer from this, which affects their lifetime. To address this challenge, [PERSON] et al. [17] propose the Energy-Aware Cluster-based Routing LEACH (EACR-LEACH) protocol for IoT networks. It uses residual energy, the number of neighbors, the distance to the sink, and the number of nodes acting as CHs. The latter is defined as the number of times a node has been a CH to control the random selection of CHs and make nodes fair in their CH load and conserve their energy. For IoT networks, the routing of data takes up a large proportion of the batteries. IoT devices manage many smart applications and must meet the needs of the applications. To obtain optimal paths that conserve device energy, [PERSON] et al. [18] propose the Robust Cluster-Based Routing Protocol (RCBRP).