# Evaluation of Green Strategies for Prolonging the Lifespan of Linear Wireless Sensor Networks
## 5 Energy-Balancing Techniques
### Energy-Efficient Routing Protocols
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Energy-Balancing** & **Key Parameters** & **Pros** & **Cons** & **Impact in LWSN** \\
**Techniques** & & & & & \\ \hline Optimal node placement [9] & Node density, communication range, and message density. & Balances communication energy optimizing the distance between nodes, thereby optimizing energy distribution. & Complex planning process; may not adapt well to dynamic environments. & Effective in LWSNs, but placement must account for the linearity of the network, message, and node densities to ensure uniform energy consumption. & Very effective in LWSNs, as adjusting power for short-range communications between adjacent nodes minimizes energy waste. Also used in achieving reliability during node failures by increasing the transmission power to jump over the failed sensor node. \\ \hline Clustering [101] & Node-to-cluster head distance, cluster size, and number of clusters. & Reduces energy consumption through data aggregation; improves scalability. & Uneven energy depletion if cluster heads are not rotated properly; overhead in maintaining clusters. & Limited effectiveness in LWSNs due to fewer path options in LWSNs imposed by linear topology. \\ \hline Energy-efficient routing protocols [102] & Residual energy and routing overhead. & Prolongs network lifetime by preventing overuse of congestion. & Suboptimal routing decisions may increase overall energy consumption; increased computational overhead. & Limited effectiveness in LWSNs due to fewer path options in LWSNs imposed by linear topology. \\ \hline Multipath routing & Path length, number of alternative paths, and route maintenance. & Increases fault tolerance and reliability, balances energy use across multiple nodes. & Increased overhead in maintaining multiple routes, higher complexity. & Less effective in LWSNs due to the minimal path options, resulting in suboptimal load balancing. \\ \hline Mobile sink [105] & Sink mobility pattern and data collection frequency. & Resoluc communication energy consumption by bringing the sink closer to nodes; prolongs network lifetime. & Increased complexity in sink movement coordination; may burden on edge nodes (gravity reduces the network lifetime). & Very effective in LWSNs by reducing the burden on edge nodes (gravity reduces the network lifetime). \\ \hline Energy neutral operation [106, 107] & Harvesting efficiency and energy availability. & Sustainable long-term operation without battery replacement or external power. & Harvested energy may be inconsistent; requires energy-harvesting hardware. & Viable for LWSNs, but effectiveness depends on the availability of energy-harvesting resources along the linear path. \\ \hline Wireless energy transfer [108, 109] & Energy transfer efficiency, charging frequency, energy replenishment rate, and positioning of charging stations. & Extends network lifespan & Requings specialized infrastructure, limited by charging range and efficiency, susceptible to interference. & Effective in LWSNs if charging stations are well-placed along the linear path, but challenges in coverage over long distances remain. \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Evaluation of energy-balancing techniques and their impact in LWSNs. Cluster-based routing organizes sensor nodes into clusters, typically with a designated cluster head (CH). The CH performs specialized functions such as data fusion and aggregation and communicates the aggregated data directly to the base station or to other CHs. The CH can be selected randomly or based on one or more criteria, and this also largely affects the WSN's lifetime. An ideal CH is the sensor node with the highest residual energy, the maximum number of neighbor nodes, and the smallest distance from the base station [110]. The goal of clustering schemes is to reduce the number of redundant communications in the WSN by reducing the number of nodes that communicate with the base station.