# High-Reliability Underwater Acoustic Communication Using an M-ary Cyclic Spread Spectrum
## 4 Experimental Results
### The Results  
The signal transmitted in the experiment consists of the LFM signal, guard interval, _PN_ code, and data part, as shown in Figure 5. Data are encoded with 336 bits of turbo-coded data, and all transmission signals have the same symbol rate. The LFM signal was used to distinguish the transmitted signals and it can also be used to approximate signal synchronization. If the LFM signal is used to find rough synchronization, the _PN_ signal is used to find fine synchronization. A DSSS signal contains one bit of information per symbol, CSK and MSS contain three bits of information per symbol, and MCSK and MCSS contain six bits of information per symbol. As stated in Table 4, there are five different types of transmission signals, as well as five signals with an artificial Doppler shift to see how the Doppler shift affects the system. We aimed to validate the efficiency of our proposed method in the channel without Doppler and the efficiency of our proposed method in the channel with Doppler by comparing them with the conclusions of the simulation. The uncoded BER results of MCSS, our proposed method, and the other four conventional signals are shown in Tables 5 and 6. The BER of transmissions without an artificial The doppler shift is shown in Table 5. Although there is no Doppler shift, due to the influence of the wind and current, a Doppler spread occurred, and the phase of each symbol changed, as seen in Figure 16a. Table 5 illustrates the BER after PLL phase compensation. The BER results of transmissions with artificial Doppler are shown in Table 6. MSS and MCSS can compensate for Doppler per symbol estimation; however, DSSS, CSK, and MCSS are unable to do so. As a result, the BER of the DSSS, CSK, and MCSK signals in all trials was 0.4-0.5. Thus, in a communication environment with a Doppler shift for each symbol, the DSSS, CSK, and MCSK signals were judged to have no meaning, and the remaining MSS and MCSS showed the BER by estimating Doppler for each symbol. The uncoded BERs of the DSSS, CSK, MSS, MCSK, and MCSS signals were 0.092, 0.0846, 0.0548, 0.0774, and 0.0525 on average, respectively, in an environment without artificial Doppler, and the uncoded BERs of the MSS and MCSS signals were 0.1071 and 0.1002 on average, respectively, in an environment with artificial Doppler. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Trials** & **MSS** & **MCSS** \\ \hline
1 & \(1.012\times 10^{-1}\) & \(8.63\times 10^{-2}\) \\
2 & \(1.041\times 10^{-1}\) & \(1.072\times 10^{-1}\) \\
3 & \(1.16\times 10^{-1}\) & \(1.072\times 10^{-1}\) \\ \hline Average & \(1.071\times 10^{-1}\) & \(1.002\times 10^{-1}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Uncoded BER of signals with Doppler shift. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameter** & **DSSS** & **CSK** & **MSS** & **MCSK** & **MCSS** \\ \hline Data rate (bps) & 10 & 30 & 30 & 60 & 60 \\ Symbol rate (sps) & 10 & 10 & 10 & 10 & 10 \\ Number of sequences & 127 & 127 & 127 & 127 & 127 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Transmission signal parameters. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Trials** & **DSSS** & **CSK** & **MSS** & **MCSK** & **MCSS** \\ \hline
1 & \(8.03\times 10^{-2}\) & \(6.55\times 10^{-2}\) & \(4.76\times 10^{-2}\) & \(6.68\times 10^{-2}\) & \(3.57\times 10^{-2}\) \\
2 & \(8.9\times 10^{-2}\) & \(8.74\times 10^{-2}\) & \(5.65\times 10^{-2}\) & \(7.03\times 10^{-2}\) & \(5.95\times 10^{-2}\) \\
3 & \(1.07\times 10^{-1}\) & \(1.01\times 10^{-1}\) & \(6.03\times 10^{-2}\) & \(9.52\times 10^{-2}\) & \(6.24\times 10^{-2}\) \\ \hline Average & \(9.21\times 10^{-2}\) & \(8.46\times 10^{-2}\) & \(5.48\times 10^{-2}\) & \(7.74\times 10^{-2}\) & \(5.25\times 10^{-2}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Uncoded BER of signals without Doppler shift. Figure 16a shows the phase change due to the influence of the Doppler spread due to ocean currents and wind as a constellation diagram of the DSSS signal.