## 6 Conclusions  
This study proposes and validates a novel routing protocol for underwater wireless sensor networks, Adaptive Power-Controlled Energy-Efficient Depth-Based Routing (APC-EEDBR), designed to overcome the limitations of existing protocols that rely solely on local information while neglecting global context and multidimensional factors, often resulting  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Protocol**} & \multirow{2}{*}{\begin{tabular}{c} **Average** \\ **Delay (s)** \\ \end{tabular} } & \multicolumn{2}{c}{\begin{tabular}{c} **Energy** \\ **Consumption** \\ **(\(\times\)100 J)** \\ \end{tabular} } & \multicolumn{2}{c}{\
\begin{tabular}{c} **Packet Delivery** \\ **Ratio (PDR)** \\ \end{tabular} } & \multicolumn{2}{c}{
\begin{tabular}{c} **Network Lifetime** \\ **(Rounds)** \\ \end{tabular} } \\ \hline APC-EEDBR & 1.63 & 39.12 & 0.892 & 761.95 \\ DBR & 2.58 & 89.85 & 0.986 & 234.10 \\ EAVARP & 1.34 & 30.29 & 0.882 & 599.50 \\ EEDBR & 4.05 & 44.16 & 0.875 & 550.50 \\ APCDBR & 1.78 & 40.86 & 0.865 & 644.88 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Performance comparison under moderate density and mobility.  
Figure 12: Impact of node speed on \(Delay_{Avg}\).  
in unstable routing and uneven energy consumption. The APC-EEDBR protocol integrates multiple node-level metrics and introduces a globally aware relay selection mechanism combined with adaptive power control, thereby enhancing overall network coordination and adaptability. In highly dynamic underwater environments, where node mobility and frequent link disruptions prevail, APC-EEDBR currently lacks explicit mechanisms to mitigate increased control overhead and path instability. To address this limitation, future work should explore the integration of opportunistic routing strategies, wherein multiple candidate receivers participate in forwarding decisions. The actual relay node is selected on the receiver side based on the local link quality, residual energy, and link stability. This receiver-driven approach is expected to improve the robustness of the protocol under frequent topology changes.  
In the future, underwater routing protocols are expected to evolve toward greater adaptability and intelligence, with a particular emphasis on mobility prediction, environmental awareness, and self-optimization. In addition, external factors, such as temperature variations and ocean currents, may impact acoustic signal propagation, introducing uncertainty into link estimation and control operations. Future improvements will explore solutions such as hybrid sensing methods, adaptive filtering techniques, and velocity-aware transmission power adjustment to further enhance the routing accuracy and network resilience in complex underwater environments. Furthermore, future work will focus on incorporating real-world measurements to improve the fidelity of underwater acoustic channel modeling, thereby enabling the design of more robust and effective routing protocols.  
Conceptualization, H.C., B.W., T.F., and B.L.; methodology, H.C., B.W., T.F., and B.L.; software, H.C.; validation, H.C., B.W., T.F., and B.L.; writing--original draft preparation, H.C.; writing--review and editing, H.C., B.W., T.F., and B.L.; visualization, H.C.; supervision, B.W.; project administration, T.F.; funding acquisition, T.F. and B.L. All authors have read and agreed to the published version of the manuscript. This research was funded by the Natural Science Foundation of Jiangsu Province (Grants No. BK20241014) and National Science and Technology Major Project of China. The data presented in this paper are available upon request from the corresponding author. The authors appreciate the constructive feedback from the anonymous reviewers, which helped improve the quality of this manuscript. The authors declare no conflicts of interest.