## 7 Conclusions  
In this paper, we investigate the design and application of underwater CPNT by constructing a \(U^{2}CPNT\) network system to address the challenges caused by the harsh underwater environment. We designed the architecture \(U^{2}CPNT\), conducted theoretical analysis, constructed a real system and carried out sea trials, demonstrating the advantages and promising potentials of the \(U^{2}CPNT\) system. * The theoretical analysis based on the Cramer-Rao bound illustrates the feasibility of the unified architecture, demonstrating that, along with an increase in communication rate, reliability, and timing accuracy, measured noise can be reduced. * The integrated design combines the CPNT service together, while it can effectively reduce hardware and software redundancy. A real system was constructed and the results of the sea trial indicate that the implemented system can provide an integrated CPNT service under the designed \(U^{2}CPNT\) framework. * We investigate the key performance parameters of positioning and navigation. We evaluated the localization error under two distinct timing drift conditions, with variance 1.671 when \(\sigma_{d}\) equals to \(1\times 10^{-3}\) and variance 0.501 for \(1\times 10^{-4}\) respectively. The results reveal that larger localization errors are primarily induced by more significant timing errors. We take the depth information transmission as an application of communication, and realize the calculation of position with 3 beacons, improving the positioning continuity by 7.68%. For velocity estimation, which is an important \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Communication** & **Positioning** & **Navigation** & **Timing** & **Networking** &
\begin{tabular}{c} **System** \\ **Implementation** \\ \end{tabular} \\ \hline \(U^{2}CPNT\) & ✓ & ✓ & ✓ & ✓ & ✓ & ✓ \\ \hline Underwater acoustic sensor & ✓ & ✓ & & & & ✓ \\ networks [9] & ✓ & ✓ & & & & ✓ \\ \hline Underwater localization [10] & & ✓ & & & & ✓ \\ \hline Subsea navigation & & & ✓ & & & ✓ \\ technologies [11] & & & ✓ & & & ✓ \\ \hline Underwater timing & & & & & ✓ & ✓ \\ techniques [12] & & & & & ✓ & ✓ \\ \hline PNT and Moonlight & & ✓ & ✓ & ✓ & & ✓ \\ navigation [13] & & ✓ & ✓ & ✓ & & ✓ \\ \hline APNT [14; 15; 16; 17] & & ✓ & ✓ & ✓ & & ✓ \\ \hline Integration of CPNT for & ✓ & ✓ & ✓ & ✓ & & \\ deep-sea vehicles [18] & & & ✓ & ✓ & ✓ & & \\ \hline Adaptive Pipeline MAC & & & & & ✓ & ✓ \\ Protocol [19] & ✓ & & & & & ✓ \\ \hline An on-demand & & & & & & ✓ & ✓ \\ scheduling-based MAC & ✓ & & & & ✓ & ✓ \\ protocol [23] & & & & & & ✓ & ✓ \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Comparison with relative studies. parameter in navigation service, the velocity estimation error is less than 1 m/s, with angle error less than 30\({}^{\circ}\), proving the navigation capability of our system. This study demonstrates that the proposed \(U^{2}CPNT\) architecture establishes a scalable framework for integrated underwater CPNT services. Although our results validate the core design principles, further research on different CPNT models and algorithms can be carried out. Meanwhile, it was observed that the appropriate design of the signal structure and the intelligent deployment algorithm are also important for the system performance and further optimization of the system, which can be valuable work in the future. Conceptualization, J.-H.C., Z.P. and L.H. ; methodology, L.H. ; software, M.L. ; formal analysis, Y.L. and L.H. ; investigation, H.W. ; data curation, M.L. and L.H. ; writing--original draft preparation, L.H. ; writing--review and editing, Y.L. and Z.P. ; visualization, L.H. and M.L. ; supervision, J.-H.C. and X.G. ; project administration, J.-H.C. and Z.P. ; funding acquisition, J.-H.C. and Z.P. All authors have read and agreed to the published version of the manuscript. This work was supported in part by the National Key Basic Research Program under Grant 2018 YFC1405800; and in part by the National Key Research and Development Program under Grant 2022 YFC2803000. Not applicable.