# Evaluation of Green Strategies for Prolonging the Lifespan of Linear Wireless Sensor Networks
## 1 Introduction
### Linear Wireless Sensor Networks  
In many WSN applications, the structure of the monitored area necessitates a linear deployment of sensor nodes, giving rise to a special class of WSNs known as linear wireless sensor networks (LWSNs) [8]. Prominent examples include border surveillance [9; 10], road monitoring [11], railway/subway monitoring [12; 13], powerline monitoring [14; 15; 16], sea/river shore monitoring [17], and pipeline monitoring [18; 19; 20; 21; 22; 23; 24]. In all the aforementioned applications, the common characteristic is that the area under consideration extends solely in one dimension [25]. Figure 3 depicts a LWSN deployed for pipeline monitoring.  
Figure 1: Relationship between IoT and WSN.  
Figure 2: Application areas for WSN.  
Linear wireless sensor networks (LWSNs) present several challenges, such as ensuring successful end-to-end delivery, providing a reasonable packet delivery timeframe, and maintaining energy efficiency. The main reason for this is that the linear topology restricts the number of neighbors and, consequently, the potential transmission routes, making data delivery more vulnerable to failure compared to traditional WSNs. In addition to critical node failures (caused by energy exhaustion of nodes closer to the sink due to an uneven load distribution), failures can also arise from an increased number of retransmissions, leading to higher packet collision rates and traffic congestion [26; 27]. Furthermore, LWSNs usually span over long distances [28], and the deployment of nodes in LWSNs often occurs in remote or inaccessible areas, such as mountain ranges, overhead transmission lines, under water pipelines, etc. [29], posing difficulties for battery replacement when the nodes become depleted [30]. Replacing the batteries of sensor nodes deployed in such areas presents significant challenges, including being labor-intensive and logistically complex to access the sensor nodes [31]. Moreover, the associated costs of frequent battery replacements contribute to the project's operational expenses, making energy efficiency a prominent concern in such applications. Additionally, depleted batteries directly hinder the project's goal of achieving continuous monitoring over extended periods, which may compromise data collection and analysis efforts. Addressing this challenge has given rise to an active research area referred to as green WSN/IoT [32; 33; 34; 35]. In green WSNs, alternative power sources (energy harvesting) and energy-efficient (energy savings) strategies are used to minimize the reliance on battery power and prolong the operational lifespan of sensor nodes. This reduces the frequency of battery replacement, reduce the amount of electronic waste (pollution), and also reduce the carbon footprint. Therefore, prioritizing energy efficiency is crucial in the design of LWSN solutions and by effectively addressing  
Figure 3: LWSN deployed for pipeline monitoring.  
energy consumption challenges, LWSN solutions can extend their operational lifetimes and enhance their reliability in monitoring and data collection applications.