## 8 Conclusions  
Due to the energy limitation of the underwater sensor nodes, we introduced an energy-efficient clustering routing protocol on the basis of the GA and the data fusion for UWSNs. The contributions were as follows. Firstly, this paper proposed the modified GA by proposing the new encoding scheme, the particular crossover operation, as well as the improved mutation operation. Secondly, this paper provided the improved BPNN by the developed momentum method to adjust the weights and biases, which is used by the CHNs to fuse the data in order to reduce energy consumption during data transmissions. Thirdly, the CHN selection operation was optimized, and the cluster formation process was improved. Finally, the experiments verified the effectiveness of our proposed EECRP in improving the network performance, and especially, the EECRP has improved the energy  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Algorithms** & **The Time Complexity** \\ \hline LEACH & \(O(n)\) \\ LEACH-ERE & \(O(n)\) \\ EGRC & \(O(n^{2})\) \\ FBCPSO & \(O(n^{2})\) \\ FCMMFO & \(O(n^{2})\) \\ EECRP & \(O(n^{2})\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: The time complexity of six algorithms.  
Figure 14: The number of received packets by the sink node (SN) versus the number of rounds for different protocols.  
efficiency by 46.5%, 26.7%, 18.8%, 8.2%, and 5.1% compared to the LEACH, LEACH-ERE, EGRC, FBCPSO, and FCMMFO, respectively.  
However, this work focuses on the simulation experiment rather than the real implementation. The explanation is that the simulation experiment is our first step of the evaluation of our proposed EECRP. The sea experiment, which is extremely complicated and expensive to perform, is our following work. We have already done some small-scale sea experiments, which are the solid foundations of large-scale sea experiments where the EECRP can be conducted. In the real implementation, lots of underwater sensor nodes and a ship on the sea surface are needed. The nodes are equipped with the sensors to sense and acquire information, the battery to provide energy, the memory device to store data, the processor to achieve controlling and processing functions, the acoustic modem to achieve underwater wireless acoustic communications, the power amplifier, the waterproof device and so on. In terms of processing, the nodes should be high-speed, stable, and energy-saving. In memory, they need to have the large storage capacity and ensure that no data are lost after the death of nodes. As for the underwater wireless communication technology, we are trying to achieve low latency, low error rate, and long-distance communications. In addition, the nodes can provide functions like data acquisition, data storage, data processing, and data transmission and reception through underwater wireless acoustic communications. The ship acts as the SN and gathers information from the nodes. What is more, because the data transmissions between CHNs and the SN consume lots of energy, we plan to utilize autonomous underwater vehicles to get close to the CHNs and gather data from them, which further saves the energy of nodes and prolongs the lifecycle of UWSNs.  
Conceptualization, X.X. and H.H.; methodology, W.W.; software, X.X.; validation, X.X., H.H. and W.W.; formal analysis, W.W.; investigation, X.X.; resources, X.X.; data curation, X.X.; writing--original draft preparation, X.X.; writing--review and editing, X.X. and W.W.; visualization, X.X.; supervision, H.H.; funding acquisition, H.H. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Key Research and Development Program of China, grant number 2018 YFC1405904.  
Not applicable.  
Data available on request due to privacy.  
The authors declare no conflict of interest.