## 3 System Model  
Designing an effective MAC layer protocol in UWSNs is essential to enhance energy efficiency, throughput, and network reliability. The suggested framework combines a 'hybrid TDMA and CSMA-CA architecture' to benefit from the strengths of each method while addressing their inherent constraints. Before detailing the hybrid architecture, the following provides an explanation of the unique advantages of 'TDMA' and 'CSMA-CA', as well as how their combined utilization enhances the effectiveness of the proposed solution. TDMA is a contention-free MAC protocol that allocates specific time slots, ensuring transmissions occur without collisions, to nodes, as noted by [41]. In underwater sensor networks (UWSNs), where acoustic communication experiences long propagation delays, TDMA provides several advantages. First, it enhances energy efficiency by minimizing idle listening and overhearing, as nodes only transmit during their assigned time slots. Second, it guarantees collision-free communication, unlike contention-based protocols, which boosts network throughput and reliability. Additionally, TDMA offers deterministic access, giving each node a predefined transmission opportunity, which is particularly beneficial for real-time and mission-critical applications. However, conventional TDMA faces challenges such as synchronization overhead and underutilization, especially in dynamic traffic conditions. CSMA/CA is a contention-based protocol that requires nodes to check the channel before transmitting to avoid collisions, unlike TDMA. This protocol offers several benefits, including adaptive traffic handling, as it provides flexible channel access, making it ideal for bursty and unpredictable traffic patterns. Additionally, CSMA/CA is easier to implement than TDMA as it does not require strict synchronization mechanisms, reducing protocol complexity. Furthermore, it allows efficient utilization of the channel as any node with data to send can access the channel, maximizing resource usage. However, even with these advantages, CSMA/CA faces drawbacks, such as collisions and increased energy consumption, due to frequent channel listening and retransmissions. The 'hybrid MAC architecture' strategically combines TDMA and CSMA-CA to optimize the MAC layer-based performance in UWSNs using a customized'superframe'. The'superframe structure' consists of the following:  
* TDMA Period: Allocated for periodic and high-priority data transmissions, ensuring deterministic and collision-free access. * CSMA-CA Period: Designed for dynamic and event-driven transmissions, allowing flexible access for bursty traffic. * Inactive Period: Nodes enter a low-power mode to conserve energy when no transmissions are required. By incorporating this hybrid structure, the proposed framework enhances energy efficiency, throughput, and adaptability to varying network conditions. The integration of TDMA ensures efficient channel allocation, while CSMA-CA handles unexpected traffic variations, providing a balanced MAC solution. The optimized UWSN communication channel employs a hybrid MAC protocol that combines CSMA/CA and TDMA, as shown in Figure 3. This framework integrates an AAC-RL strategy with Communication Channel-Optimized Adaptive Power Control (ACRLCC), enabling dynamic adjustment of network parameters in response to the evolving conditions of the underwater environment. The proposed hybrid MAC protocol's mathematical modeling formulation combines the mathematical models of CSMA/CA and TDMA to efficiently control channel access. The system operates by adapting to varying network loads, utilizing CSMA/CA in low-load conditions and TDMA in high-load conditions to ensure efficient communication. Both of these adaptions are defined in specific mathematical models, as described in the following text. In CSMA/CA, the probability of transmission, \(P_{\text{trans}}\), is modeled as a function of the contention window size, \(W\), and the transmission attempt probability, \(p\).