# Optimal Deployment of Vector Sensor Nodes in Underwater Acoustic Sensor Networks
## 2 Communication Performance Based on Single-Vector Sensors
### Communication PS Based on a Single-Vector Sensor  
A method of optimal deployment using a communication PS has been suggested in Reference [13]. A communication PS shows the spatial distribution of the communication performance [29]. Therefore, if a communication PS is used in the process to search the optimal deployment positions, the rapid computation of the search process becomes possible. In this paper, the same targeted area specified in Reference [13] was used to evaluate the optimal deployment algorithm of the single-vector sensor nodes and to compare it with the results obtained using the pressure sensor array. The size of the targeted area was again 484 km\({}^{2}\), of which the western boundary was ~10 km away from the east coast of Korea. A detailed description of the ocean environment in the targeted area, including bathymetry, water sound speed profiles, and sediment geoacoustic properties, is provided in Reference [13]. The targeted area was split up into 100 grid points. The channel impulse responses as a function of the range for eight different azimuths (every 45\({}^{\circ}\) from 0\({}^{\circ}\) North) of each grid point were simulated using the BELLHOP propagation model. The environmental, communication, and geometrical parameters used to extract the communication PS are shown in Table 1.  
The simulated channel impulse responses were convolved with the original communication sequence to simulate the communication signals. Then, BER estimates were performed for the three-channel vertical-pressure sensor array and the single-vector sensor using the demodulation process shown, as shown in Figure 4 in Reference [13] and Figure 2 in this paper, respectively. Figure 4 shows the BER performances interpolated for the eight azimuths of each grid point for the two receiver systems. The results show that the single-vector sensor performed better than the three-channel vertical-pressure sensor array. Based on these results, the range corresponding to a BER of 2% was defined as the communication range, as in our previous work [13].  
Then the communication ranges for the eight azimuths were averaged, and the mean value was defined as the communication radius for each grid point, assuming that the communication radius represents the communication performance for the grid point. Finally, the communication PS was obtained by an interpolation of the communication radii for every grid point. Figure 5a,b show the communication PS simulated for the three-channel pressure sensor array and for the single-vector sensor, respectively. The results also imply that the single-vector sensor has a better communication range compared with the three-channel pressure sensor array.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Ocean Environmental Parameters** & **Value** &
\begin{tabular}{c} **Communication** \\ **Parameters** \\ \end{tabular} & **Value** \\ \hline
**Month** & February & Symbol number & 3500 \\
**Longitude direction distance** & 22 km & Symbol rate & 1000 sps \\
**Latitude direction distance** & 22 km & Pulse shaping & Root Raised Cosine filter \\
**Wind speed** & 10 m/s & Equalizer & Adaptive DFE (RLS) \\
**Azimuth angle interval** & 45\({}^{\circ}\) & BER criterion & 2\% \\
**Grid points** & 100 & & \\
**Channel Modeling Parameters** & & **Value** \\
**Frequency** & & 10 kHz \\
**Source level** & & 140 dB \\
**Source depth** & & 2 m above the bottom \\
**Three-channel vertical-pressure** & Sensor depth & 0.5–3.5 m above the bottom \\
**sensor array** & Element spacing & 1.5 m (10 \(\lambda\)) \\
**Single-vector sensor** & Sensor depth & 2 m above the bottom \\ \hline \hline \end{tabular}
\end{table}
Table 1: The parameters used for the communication PS simulation.  
Figure 4: BER performance field for 100 grid points predicted for (**a**) the three-channel pressure sensor array, and (**b**) the single-vector sensor in the targeted area in February.