# Combined Improved CEEMDAN and Wavelet Transform Sea Wave Interference Suppression
## 1 Introduction  
In recent years, with the increasing development of ocean exploration, mastering the initiative of the ocean is conducive to occupying a favorable position in future naval battles. Countries are becoming increasingly aware of the economic value of the ocean and its important military strategic position. In order to make rational use of ocean resources and occupy the military initiative, countries need to continuously develop cross-media communication technology. Cross-media communication has many applications in maritime communication, including underwater resource exploration [1; 2; 3], marine biological population monitoring [4; 5; 6], and underwater target location and communication [7; 8; 9]. In terms of application, a robot can transmit the distribution information of undersea mineral resources to an aerial platform through cross-media communication. Scientists can place sensors on marine organisms to observe their physiological characteristics' migration law through cross-media communication. Cross-media communication refers to underwater speakers that excite a water surface micro-amplitude wave (WSAW) on the water's surface, and a millimeter wave radar system detects the vibrations of the WSAW to realize information transmission. Cross-media communication includes uplink communication and downlink communication. Uplink communication means an underwater sound source sends underwater reconnaissance information to an aerial platform. Downlink communication means an aerial platform sends instructional information to an underwater vehicle. Among them, the uplink communication pressure is heavy. The existing cross-media communication methods mainlyinclude buoy communication [10; 11], optical communication [12; 13], opto-acousto communication [14; 15; 16], and acoustic-electromagnetic communication [17; 18; 19]. Buoy communication has the problem of poor concealment, which easily exposes its position [7]. Optical communication has the problems of complex equipment and technical difficulty; at the same time, it has high requirements for water quality. Opto-acousto communication is greatly affected by foggy weather. In addition, communication technology requires the high stability of the laser platform. Acoustic-electromagnetic communication has the advantages of high concealment, all-time and all-weather operation, etc. It can be used for efficient and reliable communication between underwater vehicles and aircraft and satellites in the future. One of the real difficulties in cross-media communication is how to eliminate water surface interference, including sea wave and ship interference, and extract the water surface micro-amplitude wave (WSAW) signal. Regarding the interference suppression of cross-media communication, many research groups have analyzed interference characteristics and proposed corresponding algorithms to realize interference suppression on the water's surface. In [17], [PERSON] eliminates the interference through a band-pass filter, but it cannot effectively filter out the interference components in the communication frequency band. Underwater wireless optical communication has been proposed, and it changes the seawater turbidity and wind speed to reduce the impact of the water surface, thereby reducing the bit error rate (BER) [20]. In [21], [PERSON] applies a laser Doppler vibrometer (LDV) to detect the WSAW at the time-varying dynamic water-air interface and proposes an adaptive LDV tracking algorithm based on the principle of minimum loss to compensate for the roughness of the hydrodynamic surface. In opto-acousto communication, improved phase generation carrier technology removes the water surface fluctuation interference and the result is better. However, the interference frequency is required to be lower than 5 Hz, and the maximum disturbance amplitude is not more than 2 cm, which has great limitations in practical applications [22].