# HCLE: Hybrid Clustering Approach for Extending WBAN Lifetime
In addition, the routing protocols in WBANs only transmit the packets with a maximum of two hops. One of the key requirements for WBANs is also efficient energy utilization, considering the limited power resources of sensor nodes. The existing limitations in WBANs underscore the need for designing new routing protocols tailored to these networks. Among the different types of routing protocols, clustering-based protocols have shown promise for WBANs [3; 4; 5; 6; 22; 23; 24; 25]. These protocols group edge nodes into clusters, with a designated parent node for each cluster responsible for data aggregation and transmission to the sink node for remote management and analysis. These clustering-based protocols optimize energy usage by selecting an intermediate node (a parent node) that shortens the distance between the sensor nodes and the sink node. However, the selection criteria for the parent (forwarder) node on a round-by-round basis are based on factors that may lead to an uneven distribution of traffic among sensor nodes, potentially minimizing the network lifespan. Hence, enhancing the selection criteria for parent nodes becomes crucial for improving the overall efficiency of energy utilization in WBANs. To address the limitations in existing cluster-based routing protocols, this paper introduces a novel routing protocol, called the HCEL (Hybrid Clustering Approach for Extending WBAN Lifetime). The HCEL routing protocol combines the benefits of static clustering (i.e., fixed parent node until it depletes its energy) and dynamic clustering (i.e., flexible parent node selection) to optimize energy consumption and enhance network lifetime. The proposed HCEL routing protocol encompasses three key phases: network deployment and initialization, parent node selection, and data transmission. In the network deployment and initialization phase, the WBAN is established, and initial operations are performed to ensure the smooth functioning of the deployed nodes. Sensor nodes are strategically placed during this phase, and the network is initialized for subsequent operations. The parent node selection phase plays a key role in HCEL. It involves selecting parent nodes within the network that serve as intermediaries for data transmission from sensor nodes to the sink. The selection process is guided by an energy-efficient algorithm considering factors such as (1) node energy levels, (2) distance to the sink, and (3) the received signal strength indicator (RSSI). Moreover, the selected node must adhere to constraints, including the number of serving nodes (\(\tau\)) and the threshold value of the candidate parent nodes' energy (\(Th\)). By carefully choosing parent nodes, the HCEL approach aims to achieve balanced energy consumption and prevent the nodes from prematurely depleting their energy resources. Once the parent nodes are selected, the data transmission phase begins. Sensor nodes within the WBAN collect data from various physiological sensors and transmit them to the sink node. Critical data are transmitted directly (one hop) to the sink, while regular data are transmitted through the selected parent nodes (two hops) to the sink. The sink node acts as the central hub, receiving and processing the data for further analysis or storage. Throughout this phase, the sink node continuously monitors the energy levels of the sensor nodes. This monitoring mechanism helps to prevent node failures and prolong the overall lifetime of sensor nodes. The proposed HCEL approach offers several advantages over traditional WBAN systems as follows: (1) Combining static and dynamic clustering leverages clustering benefits, resulting in improved energy efficiency and network stability, and (2) the parent node selection process further enhances these benefits by ensuring load balancing among sensor nodes. As a result, the HCEL protocol extends the lifetime of sensor nodes, reducing energy consumption and enhancing the overall performance of the WBAN system. The paper follows a well-structured organization to present the research findings.