## 3 Interference simulation of different bandwidth signaling
### Analysis of the Spatial Distribution of the Noise Field  
The time distribution characteristics of the noise field are mainly targeted at the commonly used high-speed underwater acoustic communication frequency bands of 5 kHz-20 kHz. According to the sound field analysis, in addition to the spatial distribution of the signal field due to the interference and the interface fluctuation, the influencing factors of the spatial variation range also have the spatial distribution of the system noise field. This study investigated the spatial distribution characteristics of the noise field in the 5 kHz-20 kHz frequency band with a general volume noise model [22]. It was assumed that all noise sources were uniformly distributed on an infinite plane; then, the spatial correlation coefficient of the marine environmental noise was simulated. In the ExQD_1701 experiment, the curve of the spatial correlation coefficient with respect to depth for a 10 kHz signal for 10 h is shown in Figure 9. The black dotted line is the theoretical value given by the general model of volume noise, and the spatial correlation of noise was small at high  
Figure 8: Spatial distribution at different distances (20 kHz): (**a**) vertical distribution at 1 km, (**b**) vertical distribution at 4 km, and (**c**) vertical distribution at 8 km. Figure 7: Spatial distribution at different distances (12 kHz): (**a**) vertical distribution at 1 km, (**b**) vertical distribution at 4 km, and (**c**) vertical distribution at 8 km. frequencies. Due to the correlation, calculations were performed between 30 array elements at different vertical depths and the no. 1 surface array element; consequently, the spatial correlation coefficient curve was clearly revealed. It was found that the curve matched the theoretical value given by the volume noise model. In subsequent high-frequency noise experimental data processing, the vertical correlation between array elements could be ignored. In order to discuss the spatial distribution of wind and wave noise, the environmental noise was collected by using an array in ExQD_1701. The seabed in the experimental sea area was approximately the same level. The water depth was 40 m and the wind speed during the experiment was approximately 3 m/s. There were no other vessel activities within 5 km. Figure 10a indicates the noise field distribution of the marine environment at different depths, and Figure 10b shows the noise field distribution with the ship's self-noise. The no. 1 array element was an offshore array element, and the no. 30 array element was a near-sealed array element. The ship's self-noise had a greater impact on the frequency band below 5 kHz, which gradually decreased with the increase in depth and slightly fluctuated at high frequencies. Underwater acoustic communications often utilize high-frequency bands, with an associated 5 dB of noise fluctuations. The spatial distribution of environmental noise was not obvious and it was mainly because the surface noise source was a surface source composed of multiple noise sources. During the propagation process, the noise signals overlapped and neutralized each other with relatively small spatial fluctuation. Figure 10: Environmental noise and vertical distribution of ship self-noise: (**a**) environmental noise and (**b**) ship noise. Figure 9: Correlation coefficient with depth (10 kHz, 10 h). Figure 11 demonstrates the vertical distribution of noise at different frequencies measured using an array suspended from the side of the ship when the auxiliary ship was still working. Compared with the noise in Figure 10b, it can be considered that the noise was below 4 kHz. The noise in the frequency band was mainly the self-noise of the receiving ship. Due to this frequency band, the noise had a more obvious vertical distribution at each frequency point. As the depth increased, the noise power spectral density gradually increased, and the difference in noise spectral level could accumulate to approximately 20 dB.