# HCLE: Hybrid Clustering Approach for Extending WBAN Lifetime
## 2 Related Work
Examples of a temperature-based routing protocol in WBANs are \(M^{2}E^{2}\) (Multimode Energy-Efficient Multi-Hop protocol) [55], RE-ATTEMPT (Reliability-Enhanced Adaptive Threshold-Based Thermal-Unaware Energy-Efficient Multi-Hop protocol) [56], MATTEMPT (Mobility-Supporting Adaptive Threshold-Based Thermal-Aware Energy-Efficient Multi-Hop protocol) [57], TMQoS (Thermal-Aware Multi-Constrained Intrabody QoS routing protocol) [51], ETPA (Energy-Efficient, Thermal, and Power-Aware routing protocol) [58], ALTR (Adaptive Less Temperature Rise) [59], LTRT (Least Total Route Temperature) [60], and TARA (Thermal-Aware Routing Algorithm) [61]. The cluster-based routing protocol reduces the amount of data transmission and the distance between the sensors and the sink node, leading to reduced energy consumption and improved network lifetime. However, the choice of cluster heads may affect the network's overall performance. Examples of clustered routing protocols in WBANs include SIMPLE (Stable Increased Throughput Multihop Protocol for Link Efficiency) [24], iM-SIMPLE (Improved-SIMPLE) [23], FEEL (Forwarding Energy-Efficient Data with Load Balancing) [4], ERRS (Energy-Efficient Reliable Routing Scheme) [25], LAEEDBA (Linked-Aware Energy-Efficient routing protocol) [22], CO-LAEEDA (Cooperative-LAEEDA) [6], and DSCB (Dual Sink Approach Using Clustering in Body Area Network) [5]. On the basis of the above discussions, the cluster-based routing protocol is the most suitable for WBAN applications. This paper aims to improve the energy efficiency of the network and extend the lifetime of the network by clustering the sensor nodes into groups [35]. Each cluster has a cluster head, which serves as an intermediary node and is responsible for collecting data from the sensor nodes and forwarding it to a sink node. Table 1 summarizes the different cluster-based routing protocols employed in WBANs and compares them with our proposed routing protocol (HCEL). The table highlights essential information, such as the criteria used for parent node selection, advantages, limitations, clustering approach, and the number of sink nodes. Most cluster-based routing protocols are built on a static clustering strategy. This static approach keeps the parent node (e.g., nodes close to the sink) unchanged until it depletes its energy (i.e., dies), resulting in decreased network efficiency. In contrast, dynamic clustering involves a flexible selection and adjustment of the parent node based on the current state of the network. The choice of the parent node is dynamically modified to adapt to changes in node energy levels, connectivity, or other network conditions. Although dynamic clustering improves network performance, it often incurs additional overhead and complexity, as the cluster structure needs to be frequently updated and modified. \begin{table}
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To overcome the limitations of static and dynamic clustering, we propose an energy-efficient routing strategy called HCEL. In our routing protocol, we prioritize the selection of parent nodes based on factors like distance, residual energy, and RSSI. Unlike static clustering approaches where the same node is chosen until its energy is depleted, our protocol selects a different parent node after several data transmission rounds. Our routing protocol considers other parameters, such as the number of the nodes that the parent node can serve (\(\tau\)) and the threshold energy for all parent candidates (\(Th\)). By incorporating these factors, the selection of the parent node is adjusted based on the current state of the network, effectively combining the benefits of both static and dynamic clustering. This adjustment ensures a balanced distribution of the load across all nodes, preventing any individual node from being overwhelmed with data forwarding tasks. By combining both the static and dynamic clustering, we enhance the network lifetime, stability period, energy consumption, and overall performance.