## 3 Medium Access Control (MAC) Layered UWAC Protocols
### Comparative Analysis of MAC Layer-Based UWAC Full-Duplex Protocols
#### 3.4.4 Transmission Range  
In the shallow water region, the FD-CDMA-based protocols [46] provide the shortest transmission range of only 15 feet between full-duplex modems, pointing this area further investigation. To pass 1000 bps, the IBFD-MAC protocol [35] archives the lowest transmission range of 500 m at various water depths. In the Yellow Sea near northeastern China, the maximum transmission range of FD-DA-CSMA [30] is up to 0.5 km. However, the protocol's efficiency for new and drop nodes, as well as its implementation in a large UWAC network, must be checked. UW nodes centered on FS-MACA [37] archive 2 square kilometers of highest transmission range to transmit 100 kbps data. The transmission range of FDCA-MAC [34] ranges from 500 to 1000 m. The fact that the rise in data rate is proportional to the increase in transmission range is intriguing. The FDCP-MAC protocol [39] achieves a 3 km transmission range with a 2400 bps data rate. Suggested Cross-Layered Design Architecture Using Full-Duplex Physical and MAC-Layered UWAC Systems  
Underwater sensor networks (UWSNs) are typically made up of a variety of sensors that communicate using various protocols in order to estimate underwater activities in shallow or deep water and create a fast communication channel. The cross layer architecture can be used to deploy various FD communication based UWSNs in the ocean environment, as shown in Figure 7. The cross-layer protocol architecture allows for the efficiency of underwater acoustic networks to be optimized. It eliminates the conventional constraint that information can only be transferred between two adjacent layers, while information can be exchanged between non-adjacent layers. The PHY layer provides information about estimated SNR to the MAC layer, which assists the MAC layer in resetting the back-off timer for retransmission, resulting in energy savings and reduced network end-to-end latency. The UWSNs can function via terrestrial base stations, satellites, and floating buoys, as shown in Figure 7. Using efficient energy utilization and joint optimization of their functionalities at different layers of the protocols stack, the cross-layered architecture can provide a roadmap to higher network throughputs [72; 73; 74]. The described design focuses on energy efficiency [75; 76; 74], as energy consumption is a major concern in UWSNs, and underwater sensors are usually powered by batteries [72]. Unexpected collisions consume more battery power, resulting in greater interference in UWSNs [35]. Traditional CSMA/CA hand-shaking-based MAC protocols can effectively mitigate this issue, but they waste a lot of energy during handshaking and retransmission of control packets. The IBFD UWASNs minimize the number of control packets, resulting in increased battery performance and energy savings. A centralized network structure is also considered in Figure 7, where the data link layer considers the MAC layer algorithm and applies a cross-layer protocol architecture approach between the physical layer and the MAC layer. Via channel information input from the physical layer, the data link layer can more effectively distribute channel resources, resulting in increased channel resource usage and power savings. At the same time, the physical layer will boost communication quality by responding to data link layer power adjustment and control commands. This cross-layer design will reduce power consumption, reduce propagation delay, and increase throughput. Furthermore, further optimization of IBFD with PHY and MAC layers in a cross-layered perspective may be possible in the future [35]. Furthermore, an optimized cross-layer based on the HD CSMA/CA protocol [72] that does not use the RTS/CTS handshake for channel reservation can be implemented. However, it employs a virtual listening system to assess if the channel is busy or ideal for data transmission by listening to data frames from other nodes. The approximate SNR information provided by the PHY layer aids the MAC layer in resetting the back-off timer for retransmission.