# Energy Saving in Wireless Sensor Networks via LEACH-Based, Energy-Efficient Routing Protocols
## 4 Threshold LEACH with Sleep-Awake Scheduling Protocol
### Overview of T-LEACH\({}_{\text{SAS}}\) Architecture  
The aforementioned operation of the T-LEACH\({}_{\text{SAS}}\) protocol is based on the combined use of eight distinct processes, which are described, as follows:  
* Network Initialization and Cluster Head Selection  
At deployment, each sensor node is initialized with a fixed initial energy quota. Cluster heads are determined dynamically by using energy thresholds. Each cluster head remains active, as long as its residual energy stays above a certain threshold. When energy levels fall below this threshold, the cluster initiates a cluster head re-election process, thereby reducing overhead associated with frequent cluster head rotation. * TDMA Schedule Creation and Distribution  
Each cluster head computes a TDMA schedule to organize intra-cluster communication. The schedule assigns time slots to each cluster node in order to transmit sensed data. In order to achieve synchronization and coordination, the schedule is calculated at the beginning of each operational round and is broadcasted by the cluster heads to their respective cluster members. * Sleep-Awake Scheduling Mechanism  
Each node operates using low-power internal hardware timers, which remain active during sleep periods to accurately maintain synchronization with the TDMA schedule. After receiving their assigned timeslots, non-cluster head nodes enter sleep mode, significantly reducing idle listening energy dissipation. Low-power timers, active during these sleep intervals, trigger nodes to transition back to an awake state just before their TDMA slot, ensuring the timing of data transmission without unnecessary energy loss. Thismethod maintains synchronization across the network efficiently and also dramatically reduces the nodes' idle listening time, thus conserving significant amounts of energy. * Data Sensing, Threshold-Based Wake-Up, and Transmission Control Nodes periodically wake up according to their TDMA schedule and sense the environment. Each node implements a threshold-based sensing approach to decide on whether the sensed data require transmission. The logic is as follows: If the measured value exceeds a predefined threshold, the node proceeds to transmit its data in its TDMA slot. If the sensed value is below the threshold, the node skips the transmission step and immediately returns to sleep mode, thus avoiding unnecessary energy expenditure. This threshold-based sensing mechanism minimizes the number of transmissions, thus enhancing energy conservation. A pipeline wake-up mechanism is also implemented, where a node that has urgent data (beyond the threshold) can send a wake-up signal ahead of its regular slot, prompting the wake-up of intermediate nodes along the path towards the cluster head and, ultimately, to the base station, without waiting for the next full TDMA cycle. * Data Aggregation at Cluster Heads Cluster heads aggregate incoming data from their member nodes. Data aggregation is carried out locally within cluster heads, performing statistical methods (such as averaging, maximum/minimum detection, or more complex aggregation algorithms if required). This aggregation step reduces the quantity of transmitted data and minimizes the energy expended on longer-distance transmissions to the base station. * Energy Monitoring and Network Maintenance Cluster heads and member nodes monitor and update their residual energy levels. Using this information, cluster heads inform their suitability as heads. Nodes whose energy falls below a certain threshold are labeled \"dead nodes\" and stop participating in the network operations. * Synchronization and Clock Drift Handling Although the use of internal low-power hardware timers minimizes the need for timer recalibration to counteract potential clock drift, T-LEACH\({}_{\text{SAS}}\) in prolonged operation periodically recalibrates the nodes' clocks. This periodic recalibration, together with the initial TDMA schedule distribution from the cluster heads, ensures the synchronization of the nodes.