# Self-Adjustment Energy Efficient Redeployment Protocol for Underwater Sensor Networks
## 5 Impact of the Water Currents on the Network Deployment  
The dynamic nature of the aquatic environment leads to a continuous change in the network topology. This is due to the water currents and the surface wind [31]. For the underwater sensor network, the water currents directly affect the network deployment. These water currents, in the realistic case, change with the depth. Many research works consider network redeployment without taking into consideration the water currents. In this section, we will show the difference between considering the ideal case in which there are no water currents and the real resulting network deployment with water currents.  
Figure 1 shows the effect of the water currents on the node displacement. We suppose the sensor \(s_{i}\) in position \(A\), and its new position calculated by the deployment algorithm is \(B\). Hence, the sensor \(s_{i}\) should move from \(A\) to \(B\). However, when the sensor starts moving and takes the direction to reach \(B\), due to the water currents, this direction will deviate, and the sensor will reach position \(C\) instead.  
By simulation, we show the difference between the deployment protocol using 3D-DVFA in an ideal environment without water currents and the real deployment resulting with water currents. For the simulation, we used the simulator Aquasim, the underwater network simulator based on network simulator ns2. The number of sensors is 400 nodes deployed initially randomly at the surface of the ocean in a 3-D area. The speed of the sensor is 2.5 m/s and the speed of the water currents depends on the depth. The simulation parameters are presented in Section 7.2.  
Figure 2 shows the coverage rate achieved by the deployment of the UWSN with and without considering the water currents. Based on these results, we notice that when the deployment protocol shows the coverage rate is 98%, the real network coverage does not exceed 78%. This rate is unsatisfactory from the application point of view which aims to maximize the area monitoring and so the coverage rate. Moreover, the total distance traveled by sensor nodes during the network deployment is 5 times higher than the theoretical distance traveled by sensor nodes as shown in Figure 3.  
Figure 1: Real displacement in the presence of water currents.  
Figure 2: Coverage rate.  
Based on these results, we can conclude that the water currents heavily affect the network deployment. Hence, these water currents should be considered in the deployment protocol. Moreover, the water currents can impact the energy consumed during the deployment. In fact, if the movement towards the new position is in the same direction as the water currents, in this case, the sensor will consume less energy to reach its position. However, if the movement to the new position is against the water currents, the node will expend more energy to reach its new position.  
In the next section, we will extend the 3D-DVFA protocol to take into account the water currents and study the effect of the water currents on the energy consumed during the deployment. Our new protocol is called Self-Adjustment DVFA (SA-DVFA).