# An Optical Differential Method for Underwater Wireless Communication in Turbid Environments
## 4 Results
These facts indicate that even in a turbid natural water environment, the ODCM significantly outperforms optical intensity modulation in terms of communication distance and reliability. To achieve long-distance wireless communication underwater using visible light, most studies may resort to a higher-power light source; however, this would lead to excessive power consumption, which is not conducive to sustainable development. Table 2 compares the power consumption required per meter for the transmission of different underwater optical communication technologies. As can be seen in the results of the referenced studies, these experiments yielded good results, consuming a few tenths of a milliwatt or even a few tenths of a milliwatt per meter of power transmitted. We have succeeded in detecting and restoring weak signals using differential modulation at the transmitter end and color coordinate detection at the receiver end, with a power density of only 0.032 mW/m, which outperformed the other methods. Figure 5: Images collected at the receiving end of underwater optical communications in the 3 NTU Formazin solution using light chromaticity and intensity. Notably, this study focuses on the demonstration of ODCM and performance comparisons of conventional methods of intensity modulation. For real implementations, if a long distance is the target, the LED light source can be replaced with lasers. Also, since only two colors of light sources are involved in the color mixing in this study, the binary chromaticity for the light communication can only be selected from the line segment bounded by the chromaticity coordinates of two LEDs. For a broader selection range, that is, the gamut, red-green-blue lasers could be the ideal laser source [24]. The optimal binary chromaticity coordinates could be selected in such a way that they are farthest away from each other and show the minimum chromatic aberration as the propagation distance varies. In addition, a spectrometer is used in this study to obtain chromaticity and intensity at the same time in a single measurement so that the two quantities can be compared at the same level. However, for real applications, the spectrometer could be easily replaced with a colorimeter so that a much higher data rate can be achieved. In this paper, the influence of suspended particulate matter on optical communication in turbid waters is studied, but there are still turbulent bubbles and other factors in actual water bodies. Adding factors such as turbulence to future ODCM research experiments can better simulate real-world environments. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Light Source** & **Modulation** & **Power per Meter** & **Reference** \\ \hline
450 nm LD & Bit-power loading DMT and NE & 24 mW/m & [2] \\
450 nm LED & OFDM & 4.44 mW/m & [3] \\
527 nm LED & OFDM & 1.6 W/m & [4] \\
450 nm LD & OFDM & 0.07 mW/m & [26] \\
450 nm LD & OOK & 0.14 mW/m & [27] \\
520 nm LD & OOK & 0.25 mW/m & [28] \\
532 nm LD & Constant-Envelope & 0.33 mW/m & [7] \\
450 nm LD & I-SC-FDM & 2.09 mW/m & [29] \\
488 nm LD & 2 PPM & 0.055 mW/m & [11] \\
450 nm LED & 64-QAM & 83.3 mW/m & [30] \\ White LED & OOK & 0.032 mW/m & This work \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison between present work and previous works. Figure 6: Images collected at the receiving end of underwater optical communication in river water collected from Jing-Hang Grand Canal in Hangzhou using light chromaticity and intensity.