## 5 Simulations
### Channel Performance as a Function of Different Salinity Values  
The first simulation is related to the effect of the salinity change on the acoustic channel parameters. So, salinity fluctuation is obtained between 20-40%. Other parameters are fixed, like temperature at 29 \({}^{\circ}\)C, pH = 8, w = 5 m/s and frequency 78 kHz. The average value over all the capacities, obtained from Equation (8), of the acoustic channels of each node that communicated until the death of the first node for any network set up as a function of the salinity, ranging from 20 to 40%, is shown in Figure 4. By increasing salinity, the capacity of the acoustic channel decreases. This is because the increasing salinity affects the propagation of the acoustic communication path as it increases the absorption coefficient (increases the absorption term associated with magnesium sulfate). Increasing salinity would thus reduce the SNR ratio at the receiver and, according to [PERSON] [11], will be translated into a decrease in capacity. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Company** & **Modem** & **Frequency (kHz)** & **Tx Power (W)** & **Rx Power (W)** & **Max Range (Km)** \\ \hline AquaTec & AquaModem1000 & 7.5–12 & 20 & 0.6 & 20 \\ LinkQuest & UWM200H & 26.77–44.62 & 2 or 8 & 0.8 & 1.2 \\ EvoLogics & S2C R 48/78 & 48–78 & 5, 8, 18 or 60 & 1.1 & 1 \\ Titech & MicronDataModem & 20–28 & 7.92 & 0.72 & 0.5 \\ DSFCComm & AquaCom & 16–30 & Configurable & 0.42 & 3 \\ TeledyBenthos & SMARTModem & 9–14, 16–21 or 22–27 & NS & NS & 2–6 \\ AquaSeNT & AquaSeNTModem & 14–20 & 5–20 & 0.7 & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Commercial Underwater Acoustic Modems. \begin{table}
\begin{tabular}{c c} \hline \hline
**S2C R 48/78 EVOLOGICS** \\ \hline Depth of operation & up to 200 m \\ Range of operation & 250 m \\ Range of frequencies & 48–78 kHz \\ The model of the ray beam & Omni directional \\ Bit error rate less than & 10–10 \\ Buffer & 1 MB, configurable \\ Host interface & Ethernet/RS-232 \\ Power supply & External: 24 VDC (options for 12 VDC, 300 VDC) \\ Internal: Redrangeable battery \\ Power consumption & Tx 5.5 W/250 m range, Rx 1.4 W; Listen 5 mW, Stand-By 2.5 mW \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Company** & **Modem** & **Frequency (kHz)** & **Tx Power (W)** & **Rx Power (W)** & **Max Range (Km)** \\ \hline AquaTec & AquaModem1000 & 7.5–12 & 20 & 0.6 & 20 \\ LinkQuest & UWM200H & 26.77–44.62 & 2 or 8 & 0.8 & 1.2 \\ EvoLogics & S2C R 48/78 & 48–78 & 5, 8, 18 or 60 & 1.1 & 1 \\ Titech & MicronDataModem & 20–28 & 7.92 & 0.72 & 0.5 \\ DSFCComm & AquaCom & 16–30 & Configurable & 0.42 & 3 \\ TeledyBenthos & SMARTModem & 9–14, 16–21 or 22–27 & NS & NS & 2–6 \\ AquaSeNT & AquaSeNTModem & 14–20 & 5–20 & 0.7 & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Technical specification of S2C R 48/78 EVOLOGICS [24]. Figure 5 shows the performance of the total delay versus salinity, calculated according to the formula in [25], brought here from Equation (22). With the increase of salinity coefficient, the total delay decreases. This is because the predominant component in the total delay is the propagation delay. As salinity increases the speed of sound propagation, the signal will require a shorter total time to propagate between the transmitter and the receiver. The results of simulations, following the algorithm introduced in Figure 3, is presented in Figure 6 and shows the lifetime performance of the algorithm depending on salinity, where as input are taken in consideration the energies presented in Table 3.  
Figure 4: Average capacity for different values of salinity. Figure 5: Total delay for different values of salinity. Figure 6: Lifetime for different values of salinity. The simulated results show that with the increase of salinity value, the capacity of the acoustic channel decreases, so the modem will required more time to transmit the data.