# Combined Improved CEEMDAN and Wavelet Transform Sea Wave Interference Suppression
## 4 Experimental Results  
The measured results show that the algorithm has the ability to suppress sea wave interference. In this section, the experimental data were acquired to study the performance of the algorithm and the performance indicators of the cross-media communication were analyzed. Specifically, we designed a cross-media communication system, which in  
Figure 2: Flowchart of the sea wave interference algorithm. cludes an underwater sound source device that transmits underwater signals, a millimeter wave radar that receives radio frequency signals, a variable fan that forms the sea wave interference, and a host for signal processing. In Figure 3, the signal generator transmits the signal to the underwater speaker through the power amplifier and excites the water's surface to form the WSAW. The variable fan is adjusted to form the sea wave interference on the water's surface, and the WSAW is superimposed. The radar transmits the FMCW signal with a center frequency of 34.6 GHz and a bandwidth of 1.2 GHz to measure the change in the water surface vibration. Figure 4 shows an actual cross-media communication scenario for interference suppression. The experiment was carried out in an open place. The transmitting and receiving antennas illuminated the water surface vertically, and each was placed 1 m away from the water's surface. The underwater speaker was placed in an experimental water tank with a depth of 0.28 m. The antenna phase center was aligned with the center of the underwater speaker. The Ka-band FMCW radar prototype for the cross-media communication was designed by the National Key Laboratory of Microwave Imaging Technology, Chinese  
Figure 4: Interference suppression experiment’s platform construction. Figure 3: Schematic diagram of the experimental system. Academy of Science. The radar utilized a two-horn antenna type, as presented in Figure 4. The key parameters of the cross-media communication are shown in Table 1.  
In this section, we set up an experiment to verify the effectiveness of the improved algorithm. We considered the influence of the sea waves caused by the different wind speeds of the variable fan on the interference suppression algorithm, and we took the filtering method as a comparison [17] and the BER as the communication indicators to evaluate the effectiveness of the algorithm. The variable fan was set to two conditions: strong wind (4 th gear) and weak wind (1 st gear). Figure 5a shows the original echo matrix of the received signal when the variable fan was in 4 th gear, and Figure 5b is the range change containing the WSAW and sea wave interference. The ordinate axis represents the slow time, and the abscissa axis is the distance from the radar to the water's surface. From the echo matrix, it is clear that there was a high power reflection from the water's surface. The bandwidth of the transmitted signal was 1.2 GHz, and the width of the range resolution unit was 0.125 m. If the sea wave interference exceeded one range bin, the result is shown in Figure 5a. In the process of extracting the phase, there was the phenomenon of cross range bin. The phase of the range bin cannot represent the actual water surface vibration, while the strongest scattered power represents the actual water surface's reflected power. During the experiment, due to the limitations of the size and power of the variable fan, the sea wave interference caused by the wind did not exceed 0.5 m. Therefore, the \begin{table}
\begin{tabular}{l c} \hline \hline
**Parameter** & **Value** \\ \hline Distance from radar to water & 1 m \\ Distance from speaker to water & 0.28 m \\ Sound pressure level & 110 dB \\ Transmitting frequencies & 100 Hz to 200 Hz \\ Center frequencies & 300 Hz to 400 Hz \\ Bandwidth & 34.6 GHz \\ Pulse repetition time & 1.2 GHz \\ Number of fast time samples & 8 us \\ Number of slow time samples & 400 \\ Number of slow time samples & 343,750 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters of the cross-media communication.