# Optimization of Acoustic Communication Links for a Swarm of AUVs: The COMET and NEMOSENS Examples
## 5 Physical Layer
### Optimization Evaluation
#### 5.4.2. KAU1 Channel  
Another considered scenario is the KAU1 channel (Kauai Acomms MURI 2011) [34; 35]. This channel was recorded in Kauai, HI, USA. All the information relative to this experiment, and that are needed for the optimization procedure, are shown in Table 6.  
\begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{3}{c}{**Input Parameters**} \\ \hline \(f_{\text{c}}\) & 6 kHz \\ \(B\) & 3 kHz \\ \(c\) & 1500 m/s \\ \(p\) & 1.14 m/s \\ \(p_{\text{w}}\) & 106 m \\ \(p_{\text{Tx}}\) & 45 m \\ \(p_{\text{Rx}}\) & 97 m \\ \(d_{\text{Tx,Rx}}\) & 1080 m \\ \hline \hline \end{tabular}
\end{table}
Table 6: KAU1 channel conditions used for the optimization.  
Figure 12: Corresponding overhead for each parameters pair for BCH1 channel.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{5}{c}{**Max. Overhead (\(\rho_{\text{max}}\))**} \\ \cline{2-6}  & **0.1** & **0.15** & **0.2** & **0.25** & **0.3** \\ \hline Proposed method & \((256,5)\) & \((256,10)\) & \((128,8)\) & \((128,10)\) & \((128,12)\) \\ Genie-aided method & \((256,5)\) & \((256,10)\) & \((128,8)\) & \((128,10)\) & \((128,12)\) \\ \hline Equal results & yes & yes & yes & yes & yes \\ \hline \hline \end{tabular}
\end{table}
Table 5: Parameters chosen by each method for BCH1 channel.  
Having this information, the optimization algorithm is executed. For this case, the following values were considered: \(N_{\text{sub}}=\{128,256,512\}\) subcarriers, and \(T_{\text{CP}}=\{5,10,18,25,30,35,41\}\) ms. The optimized results are presented in Table 7.  
For evaluating these optimized results, simulations using the genie-aided approach were performed. We transmitted 14 frames with a 1 s duration. Each simulation was repeated 50 times, and the results are shown in Figure 13. Figure 14 contains the overhead value associated to each point of the previous figure. So, the benchmark parameters are selected for each overhead value.  
Table 8 shows results for both optimized and benchmark approaches. The majority of the parameters obtained with our method matches with the genie-aided results.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{5}{c}{**Maximum Overhead (\(\rho_{\text{max}}\))**} \\ \cline{2-5}  & **0.1** & **0.15** & **0.2** & **0.25** & **0.3** \\ \hline \(T_{\text{CP}}\) (ms) & 18 & 10 & 10 & 25 & 35 \\ \(N_{\text{sub}}\) & 512 & 256 & 128 & 256 & 256 \\ \(T_{\text{sym}}\) (ms) & 170.6 & 85.3 & 42.6 & 85.3 & 85.3 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Optimization parameters considering the KAU1 channel.  
Figure 13: Results for KAU1 channel considering the genie\(-\)aided approach.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{5}{c}{**Max. Overhead (\(\rho_{\text{max}}\))**} \\ \cline{2-5}  & **0.1** & **0.15** & **0.2** & **0.25** & **0.3** \\ \hline Proposed method & \((512,18)\) & \((256,10)\) & \((128,10)\) & \((256,25)\) & \((256,35)\) \\ Genie-aided method & \((256,5)\) & \((256,10)\) & \((256,10)\) & \((256,25)\) & \((256,35)\) \\ \hline Equal results & no & yes & no & yes & yes \\ \hline \hline \end{tabular}
\end{table}
Table 8: Parameters chosen by each method for KAU1 channel.