# Evaluation of Green Strategies for Prolonging the Lifespan of Linear Wireless Sensor Networks
## 2 Framework of Linear Wireless Sensor Networks  
### Classification of LWSNs  
A LWSN is a special class of WSN, characterized by its distinct topology, where nodes are arranged in a straight or near-straight line, creating unique challenges in routing,energy management, and network reliability [8]. Unlike traditional WSNs, which are often designed for multi-dimensional topologies or random deployments, LWSNs are optimized for applications where monitoring follows a linear path, making energy efficiency and routing optimization critical [39]. In addition to its distinct topology, LWSNs also differ from traditional WSNs in terms of node heterogeneity. While traditional WSNs may feature homogeneous nodes with similar roles, LWSNs often comprise a mix of different types of nodes. Nodes in a LWSN are categorized based on their roles in the network, which impacts how data are gathered and transmitted. [PERSON] et al. [8] identified three primary types of nodes in LWSNs:  
1. Basic Sensor Nodes (BSNs): These are the standard sensing units in the network. Their primary function is to collect data from the environment and transmit it to other nodes for further processing. BSNs are typically energy-constrained, with limited communication ranges and computing power, making energy efficiency essential for extending the network's lifespan. 2. Data Relay Nodes (DRNs): These nodes act as intermediaries between the BSNs and the data dissemination nodes. Their function is to forward data collected by BSNs along the linear path, ensuring that data reach their final destination (the central processing system). DRNs help maintain network connectivity over long distances, and they typically have more power than BSNs. 3. Data Dissemination Nodes (DDNs): These are high-level nodes responsible for collecting data from DRNs and transmitting the data to the base station or central monitoring system. They have stronger processing capabilities and higher energy reserves than the other types of nodes, enabling them to manage large amounts of data and handle long-range communication. These nodes make use of long-range wireless communication technologies such as LoRa, satellite, cellular, etc. According to the study by [PERSON] et al. [8], LWSNs can be classified both topologically and hierarchically. A LWSN from a given topological category can belong to any of the three hierarchical categories depending on the application. From a topological point-of-view, the authors classified LWSNs under three categories: thin, thick, and very thick LWSNs. In thin LWSNs, sensor nodes are sparsely deployed along the linear path, resulting in minimal coverage and reduced redundancy. These networks are suitable for applications where only a basic level of monitoring is required, such as pipeline and powerline monitoring [40]. Thick LWSNs feature a moderate density of nodes along the monitored path, providing greater redundancy and more robust monitoring. They are commonly used in scenarios requiring higher data reliability, such as railway or highway monitoring [39]. Very thick LWSNs have a high density of sensor nodes, ensuring comprehensive coverage and redundancy. These networks are typically used in critical infrastructure monitoring, such as border surveillance or high-security installations, where data loss and network failure are unacceptable [41]. From a hierarchical point-of-view, the authors classified LWSNs under three categories: one-level, two-level, and three-level. In one-level LWSNs, there is no hierarchy among the nodes, with all nodes having the same role (sensing, aggregation, and compression) and transmitting data directly to a central base station or processing node. Two-level LWSNs introduce a basic hierarchical structure, where BSNs relay data to DRNs, which perform aggregation and then forward the information to a DDN for further processing. In three-level LWSNs, a more complex hierarchy is established, with multiple layers of data transmission.