# Evaluation of Green Strategies for Prolonging the Lifespan of Linear Wireless Sensor Networks
## 4 Energy Conservation Techniques
### Network-Level-Focused Energy Conservation Schemes
#### 4.2.2 Energy-Efficient Routing  
The goal of routing is to establish an effective path for data exchange between sensor nodes and the base station. This introduces certain overheads and entails energy consumption, particularly for the nodes in close proximity to the base station. In WSNs, a key design consideration for routing algorithms revolves around ensuring energy efficiency. Energy-efficient routing in WSNs refers to the implementation of routing protocols and strategies that optimize the energy consumption of sensor nodes during data transmission. This requires the design of routing mechanisms that minimize energy dissipation, reduce communication overhead, and ultimately extend the operational lifetime of the entire WSN.  
Energy-efficient routing techniques play an important role in optimizing communication processes, minimizing energy consumption, and ultimately extending the lifetime of WSNs. In the literature, three notable strategies for achieving energy savings at the network level are cluster-based routing, data-centric routing, and geographic-based routing [62; 38; 65].  
Cluster-based routing organizes the sensor nodes into clusters, with each cluster having a designated cluster head. Nodes within a cluster communicate with their respective cluster head, which, in turn, communicate with the base station or sink. This hierarchical structure facilitates energy savings through localized communication and efficient data aggregation. The rationale behind cluster-based routing lies in reducing the overall communication distance, minimizing the number of node-to-sink transmissions, and enabling energy-aware management within clusters. By aggregating data at the cluster level before forwarding it to the sink, redundant transmissions are avoided, leading to energy savings [94; 95; 96].  
Data-centric routing revolves around the concept of organizing communication around the data rather than the nodes. Nodes collaborate to efficiently route data toward the sink based on the content or attributes of the information being transmitted. The rationale for data-centric routing is to minimize unnecessary transmissions by focusing on the data of interest. This strategy is particularly useful in applications where specific types of data need to be gathered or monitored, as it optimizes energy consumption by transmitting only relevant information. Data-centric routing schemes provide benefits such as selective data transmission and enhanced energy efficiency [97].  
Geographic-based routing relies on the spatial information of nodes to determine the optimal path for data transmission. Nodes use location data to forward information towards the destination, often leveraging geographic coordinates or proximity-based strategies [98]. The rationale behind geographic-based routing is to exploit the physical positions of the nodes to minimize communication distances. This approach is particularly beneficial in scenarios where the geographic location of the nodes correlates with the efficiency of communication paths. Geographic-based routing schemes provide benefits such as shorter communication paths, adaption to node mobility, and scalability.  
The impact of cluster-based routing is less effective in LWSNs compared to traditional WSNs because the number of multi-hop transmissions is not greatly reduced since the linear topology prevents the creation of large clusters. Data-centric routing can be effective in LWSNs as it has the capability to reduce the number of multi-hop communications. Geographic routing has little or no effect on LWSNs because of the limited routing options in LWSNs imposed by the linear topology. Routing in LWSNs is more concerned with reliable data delivery rather than the shortest path since there are just two routing options in LWSNs: forwarding to the left or forwarding to the right.