# A Survey on Physical Layer Techniques and Challenges in Underwater Communication Systems
## 5 Discussion  
UWAC is a rapidly evolving field that has the potential to significantly impact a range of important applications in the marine environment, such as ocean exploration, environmental monitoring, and underwater surveillance. Recent trends and important research in UWA have focused on improving the reliability, efficiency, and data rate of UWC systems, while also addressing the unique challenges of the underwater environment. One of the key trends in UWAC is the development of new modulation techniques that can improve the spectral efficiency and robustness of communication systems. FBMC is one such technique that has shown promise in UWAC, as it can provide high spectral efficiency and improved resistance to multipath interference. Another trend is the use of cooperative communication, which involves multiple nodes working together to improve the reliability and efficiency of UWCs. Yet another important area of research in UWAC is the development of new networking protocols and routing algorithms that are optimized for the underwater environment. WSNs are becoming increasingly important in UWC for applications, such as environmental monitoring and underwater surveillance. However, WSNs face unique challenges in the underwater environment, such as limited energy resources and variable network topologies, that need to be addressed to ensure reliable and efficient communication. Energy harvesting is also an important area of research in UWAC, as it can provide a sustainable source of energy for UWC systems. Researchers are exploring a range of techniques for energy harvesting, such as solar energy, thermal energy, and vibration energy, to power UWC systems. Despite these advancements, there are still significant challenges that need to be addressed in UWACs. One of the major challenges is the limited bandwidth and low data rates of UWC systems. This can limit the amount of information that can be transmitted, which is a significant limitation for applications, such as underwater video streaming and remote operation of underwater vehicles. Another challenge is the high levels of noise and distortion in the underwater environment. UWC must contend with a range of noise sources including ambient noise, noise from marine life, and noise from other UWC systems. These noise sources can significantly affect the quality and reliability of UWC systems, making it difficult to transmit and receive data accurately. Finally, the transmission range of UWC systems is another challenge that needs to be addressed. UWA signals can attenuate rapidly, making it difficult to maintain communication over long distances. This is a significant limitation for applications, such as remote monitoring of ocean currents and real-time tracking of underwater vehicles. Table 5 indicates the notable contributions of the physical layer of UWAC. It is concluded that UWAC is a rapidly advancing field that is heading towards more reliable, efficient, and high-speed communication systems. However, there are still significant challenges that need to be addressed, such as limited bandwidth, noise, and distortion in the underwater environment, as well as the limited transmission range of UWC systems. Future research in UWAC will need to address these challenges to enable the development of more advanced and effective communication systems for the marine environment.