# Data Access Based on a Guide Map of the Underwater Wireless Sensor Network
## 7 Conclusions  
With the emphasis on effective safeguarding of national marine rights and interests, the upsurge in marine economic development, and the significant progress in wireless sensor networks, underwater wireless sensor networks (UWSNs) are receiving increasing attention. Underwater acoustic communication is mainly used for UWSNs, which are characterized by low bandwidth, high delay and a higher bit error rates. For specific applications, there is a type of UWSN that can monitor real-time events and application data in the deployment area. It is necessary for the observation node to quickly obtain the events and specific application data it is concerned with in cases such as underwater target monitoring and emergency rescue. It is challenging to store data efficiently generated by sensor nodes, and for specific application data and events to be accessed as quickly as possible by the user while extending the lifetime of the network as much as possible.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Item** & **Our Work** & **Work [15; 16]** & **Work [19; 20; 35]** & **Work [21; 37]** & **Work [31; 36]** \\ \hline Data storage & \(\surd\) & \(\surd\) & \(\times\) & \(\times\) & \(\times\) \\ Data & – & \(\surd\) & \(\surd\) & – & – \\ aggregation & – & \(\times\) & \(\surd\) & \(\times\) \\ Data query & \(\surd\) & – & \(\times\) & \(\surd\) & \(\times\) \\ Data & – & \(\times\) & \(\surd\) & – & \(\surd\) \\ discovery & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: DAGM compared with some other works.  
Figure 8: Results of different deployment area size.  
In this paper, the data access based on a guide map (DAGM) method for UWSNs is proposed. In DAGM, metadata is used to describe the data content abstract and storage location abstract. The center ring is based on the shortest average query path of the network, and thus, the metadata is stored in the center ring nodes, then forming a data map of the network. In the process of data query, DAGM chooses the nearest center ring from the user to deal with the query sentence, so that the user can quickly access the specific application data and events that it is concerned with. The results of the simulated experiment show that DAGM provides quicker user access for the specific application data and events, and reduces the total energy consumption of the network while effectively prolonging the lifetime of the network.  
In future work, we will mainly focus on how to improve the storage efficiency, decrease the query time and energy consumption of networks under practical underwater conditions. In addition, our approach can support data aggregation and data discovery. Then we will adaptively improve the data map and metadata mechanism on DAGM for them, and provide a data access method with full functions and performances efficiency for UWSNs. [PERSON] et al. [48] have proposed a new way to look at cognitive access in underwater acoustic communication, and consider it a new research field. We will also improve our approach for this theme in the near future.  
This work is sponsored by the National Natural Science Foundation of China under Grant No. 61502037, 61772152, 11374072 and 61371171 the Basic Research Project No. JCKY2016206B001, JCKY2014206C002 and JCKY2016604C010, and the China Scholarship Council. [PERSON] and [PERSON] conceived and designed the research; [PERSON] and [PERSON] contributed experiment. [PERSON] and [PERSON] analyzed the data and performed the research; [PERSON] and [PERSON] wrote the paper. The authors declare no conflict of interest.