## 3 Simulation Results  
The optimal deployment performance of the sensor nodes based on the communication PS was simulated for two different seasons, winter (February) and summer (August), in the targeted area located off the eastern coast of Korea. Optimal deployment in our simulation means the sensor deployment having a maximized communication coverage while maintaining connectivity of the sensor nodes. Here, the communication coverage rate is defined as the ratio of the area of communication coverage by the sensor nodes to that of the targeted area.  
Figure 11 shows examples of the simulation results of optimal deployment for the two different seasons. The parameters used in the simulation are given in Table 1. The parameters belong in  
Figure 10: **(a)** Example showing the convergence progress of the sensor nodes. **(b)** Sensor positions after optimal deployment (blue dots). Green circles indicate the communication radii of the sensor nodes.  
Figure 9: Flow chart of the VFPSO algorithm for the search of the optimal deployment positions for the sensor nodes.  
four sub-categories: environmental parameters; channel modelling parameters; communication parameters, and; optimal deployment parameters. For the simulation, 100 sensor nodes were used. As an initial step, 100 sensor nodes were randomly distributed in the targeted area, as shown in Figure 11a. The VFPSO search algorithm was then applied. The deployment results for February and August are displayed on their communication PS, which are illustrated in Figure 11b,c, respectively. The communication coverage rate for February was estimated to be 85.2%, which is higher than that for August (estimated to be 80.6%). This result is reasonable because the ocean condition of the targeted area in February provides a better underwater communication environment than that in August, as mentioned in Section 2.3.  
Another important point to be examined is the connectivity among the sensor nodes, which is crucial for effective data communication of the UWASN system. The connectivity among the sensor nodes was estimated for the final deployment scheme to verify the performance of the VFPSO algorithm. The distance between each sensor node and its neighboring sensor nodes was compared to the communication threshold defined in Section 2.4, and the results for the two seasons are shown in Figure 12. The solid lines between sensor nodes indicate that effective two-way communication is possible. For both cases, 100% connectivity was achieved. Consequentially, the sensor nodes were positioned within the high communication performance area to achieve the maximal communication coverage rate, with intervals varying between 1.5 and 2.0 km for both seasons.  
\begin{table}
\begin{tabular}{l l l l} \hline \hline
**Environmental Parameters** & **Value** & **Channel Modeling Parameters** & **Value** \\ \hline Month & 2, 8 & Frequency & 10 kHz \\ Longitude direction distance & 22 km & Source level & 140 dB \\ Latitude direction distance & 22 km & Source depth & 2 m above the bottom \\ Wind speed & 10 m/s & Receiver depth & 0.5–3.5 m above the bottom \\ Azimuth angle interval & 45\({}^{\circ}\) & (Three vertical receiver array) & 1.5 m (10 \(\lambda\)) \\ Grid points & 100 & Element spacing & 1.5 m (10 \(\lambda\)) \\ \hline
**Communication Parameters** & **Value** &
\begin{tabular}{l} **Optimal Deployment** \\ **Parameters** \\ \end{tabular} & **Value** \\ \hline Symbol number & 3500 & Loop number & 50 \\ Symbol rate & 1000 sps & Sensor node number & 100 \\ Pulse shaping & Root Raised Cosine filter & Weight value of attractive force & 0.01 \\ Equalizer & Adaptive DFE(RLS) & Weight value of repulsive force & 0.5 \\ BER criterion & 2\% & Acceleration weight & 1 \\ \hline \hline \end{tabular}
\end{table}
Table 1: The parameters used in the optimal deployment simulation.  
Figure 11: Examples of the optimal deployment simulation using 100 sensor nodes. (**a**) Randomly deployed initial positions. (**b,c**) are the optimal deployment results in February and August, respectively.