This paper focuses on enhancing the energy efficiency of Wireless Sensor Networks (WSNs) by modifying the Medium Access Control (MAC) layer. The primary goal is to extend the network's lifetime by minimizing energy consumption and delay in packet transmission. The proposed protocol, Adaptive SMAC, is based on the Sensor Medium Access Control (S-MAC) and introduces several improvements: 1. **Low Duty Cycle Operation**: Nodes operate in a low duty cycle to reduce energy consumption. 2. **Common Sleep Schedules**: Nodes synchronize their sleep schedules to minimize control overhead and enable adaptive wake-up. 3. **Coordinated Sleeping**: Coordinated sleeping among neighboring nodes reduces latency and control overhead. 4. **Contention-Based Mechanism**: The protocol uses a contention-based approach similar to CSMA/CA, including virtual and physical carrier sense, and RTS/CTS exchange. The paper evaluates the performance of Adaptive SMAC through simulations using NS-2 under various topologies and traffic conditions. Key findings include: - **Energy Consumption**: Adaptive SMAC achieves significant energy savings, especially in low traffic scenarios. - **Latency**: While Adaptive SMAC introduces additional latency due to periodic sleep, it performs well in low traffic conditions and shows improved latency compared to the 802.11 MAC protocol in high traffic scenarios. - **Cross-Layer Design**: An alternative design, Adaptive Cross-Layer SMAC (MAC-CROSS), is proposed to further enhance energy efficiency by optimizing the interaction between the MAC and routing layers. The results demonstrate that Adaptive SMAC is effective in extending the network's lifetime and improving energy efficiency, making it a promising solution for WSNs.This paper focuses on enhancing the energy efficiency of Wireless Sensor Networks (WSNs) by modifying the Medium Access Control (MAC) layer. The primary goal is to extend the network's lifetime by minimizing energy consumption and delay in packet transmission. The proposed protocol, Adaptive SMAC, is based on the Sensor Medium Access Control (S-MAC) and introduces several improvements: 1. **Low Duty Cycle Operation**: Nodes operate in a low duty cycle to reduce energy consumption. 2. **Common Sleep Schedules**: Nodes synchronize their sleep schedules to minimize control overhead and enable adaptive wake-up. 3. **Coordinated Sleeping**: Coordinated sleeping among neighboring nodes reduces latency and control overhead. 4. **Contention-Based Mechanism**: The protocol uses a contention-based approach similar to CSMA/CA, including virtual and physical carrier sense, and RTS/CTS exchange. The paper evaluates the performance of Adaptive SMAC through simulations using NS-2 under various topologies and traffic conditions. Key findings include: - **Energy Consumption**: Adaptive SMAC achieves significant energy savings, especially in low traffic scenarios. - **Latency**: While Adaptive SMAC introduces additional latency due to periodic sleep, it performs well in low traffic conditions and shows improved latency compared to the 802.11 MAC protocol in high traffic scenarios. - **Cross-Layer Design**: An alternative design, Adaptive Cross-Layer SMAC (MAC-CROSS), is proposed to further enhance energy efficiency by optimizing the interaction between the MAC and routing layers. The results demonstrate that Adaptive SMAC is effective in extending the network's lifetime and improving energy efficiency, making it a promising solution for WSNs.