# Evaluation of Green Strategies for Prolonging the Lifespan of Linear Wireless Sensor Networks
## 3 Classification of Energy Management Techniques for Prolonging WSN's Lifetime
### A Review of Taxonies for Classifying Energy Management Techniques in WSN
The techniques for minimizing energy consumption during network activities include energy-efficient routing protocols and the implementation of mobile sinks, while the techniques for minimizing energy consumption at the node level include duty cycling techniques (radio optimization, sleep/wake-up schemes, transmission power control, dynamic voltage frequency scaling), and data-driven approaches (in-network processing, data compression, data aggregation, data prediction, hierarchical sensing, adaptive sampling, and model-based active sensing). All the techniques presented in this study are principally involved with energy savings, except for techniques such as mobile sink, energy-efficient routing protocols, and transmission power control, which can also be used for balancing the battery residual energy of the sensor nodes in the WSN. In another study, [PERSON] et al. [38] carried out a review of energy efficiency in WSNs. They provided a taxonomy for energy management techniques that is similar to that presented in [36], except for the inclusion of battery depletion, which included energy-harvesting and wireless-charging techniques. [PERSON] et al. [65] developed a taxonomy that classified energy management techniques into battery management schemes, transmission power management schemes, system power management schemes, and miscellaneous. The battery management strategies include techniques that seek to leverage the internal characteristics of batteries to reclaim their charge, aiming to optimize the quantity of power supplied by the energy source. They range from node energy management schemes that dynamically vary the power supplied to the node depending on the workload to energy-balancing schemes that strive to attain a balance between the energy generated and energy consumed. The transmission power management schemes focus on techniques that restrict the transmission power of sensor nodes using parameters such as battery residual energy, energy-harvesting rate, etc. They range from the MAC layer management schemes to energy-aware routing schemes. The system power management schemes involve techniques that achieve a significant reduction in power consumption via efficient hardware design by using energy-efficient processors and peripherals that possess smart power-saving features. These techniques range from processor power management to device management. Finally, the miscellaneous schemes, according to the authors, involve techniques ranging from load balancing, duty cycling, mobile sink, and cross-layer optimization. The techniques presented in this study can be categorized into two main groups: techniques that seek to reduce the energy consumption at the node and network levels and techniques that seek to ensure a balance in the battery residual energy of all the sensor nodes in the network. The battery management and system management schemes seek to reduce the energy consumption at the node level and, therefore, belong to the former, while the transmission power management schemes and miscellaneous schemes, such as load balancing and mobile sink, seek to balance the residual battery energy of all the nodes in the network and therefore belong to the latter. This study did not discuss any techniques for prolonging the WSN's lifetime by scavenging energy from external sources. In [37], [PERSON] et al. reviewed techniques for prolonging the lifetime of the WSN. [PERSON] et al. [34] carried out a similar review, where they reviewed current trends in green wireless sensor networks. Both studies, [34; 37], categorized energy management techniques for prolonging the WSN's lifetime into energy conservation, energy harvesting, and energy transfer/charging techniques. The energy conservation techniques aim to extend the lifetime of the WSN by minimizing energy consumption at the sensor node level or network level while the WSN continues to operate as required.