# Self-Adjustment Energy Efficient Redeployment Protocol for Underwater Sensor Networks
## 3 Assumptions  
In this research, we suppose that each sensor node in the UWSN has the ability to sense, communicate, and change its position by moving freely in the 3D network area [6; 7]. For underwater communication, acoustic modems are used to communicate between underwater sensors and between underwater sensors and the surface stations [3; 4]. The sensing capability of the underwater sensors depends on the application target, and the sensing technologies can include sonar, cameras, etc. For the underwater displacement, we suppose that for each sensor, an underwater robot serves as a vehicle that carries this sensor and enables its deployment in the network area. Recent research is focused on the development and enhancement of underwater robots' movement capabilities in the underwater environment, as presented in [29; 30]. Each sensor node has a sensing range \(R_{s}\) and a transmission range \(R_{t}\).  
We assume that the UWSN is composed of \(n\) underwater sensor nodes scattered randomly on the surface of the monitored area. The sensor node set is \(S\), where \(S=\{s_{1},s_{2},\ldots,s_{n}\}\).  
The UWSN area is 100% covered if any point in the 3D network area is at least covered by one sensor node. A point \(P\) in the network area with the coordinate \((x,y,z)\) is said to be covered, if there exists a sensor node \(s_{i}\) with the coordinate \((x_{i},y_{i},z_{i})\) such that \(d(P,s_{i})<R_{s}\), where \(d(P,s_{i})\) is the Euclidean distance between \(P\) and \(s_{i}\).  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Reference** & **Algorithm** & **Coverage** & **Connectivity** & **Energy Efficient** & **Water Currents** \\ \hline [10] & Practical Swarm & ✓ & - & - & - \\ \hline [12] & Distributed virtual & ✓ & ✓ & Number of messages & Added as a force in \\  & force algorithm & ✓ & ✓ & sent and received & the deployment protocol \\ \hline [24] & Distributed hybrid & ✓ & ✓ & Reduce the total node moving & - \\  & fish swarm optimization & ✓ & ✓ & distance during node deployment & \\ \hline [25] & Connected Tree & ✓ & ✓ & Communication energy and & Considered only for the \\  & & & & node displacement energy consumption & connectivity but not in \\  & & & & the deployment protocol \\ \hline [26] & Connected dominating set & ✓ & ✓ & - & - \\ \hline \multirow{3}{*}{[27]} & Fully Distributed & & & Reduce sensors & Redundant sensors \\  & Deployment & ✓ & ✓ & displacement by & to resolve the water currents \\ \cline{1-1}  & Algorithm & & & moving to the & coverage and connectivity holes but not \\ \hline \multirow{3}{*}{[28]} & Hybrid multi-objective & & & & closede in the deployment protocol \\  & node deployment & ✓ & - & & mobility, sensing. \\ \cline{1-1}  & & & & and data communication processes & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Comparison of state-of-the-art Free Mobility Deployment solutions in UWSNs.  
Moreover, we suppose that \(R_{t}\geq\sqrt{3}R_{s}\) since it is proven that when the above relation between \(R_{s}\) and \(R_{t}\) is applied, the connectivity will be implied if the coverage is achieved. Thus, if network coverage is ensured, network connectivity will also be ensured.