Characterization of signal response for surface water movements in underwater optical wireless communications

Underwater communications has a lot of benefits. There are already existing technologies that use this type of communication, but the concerns are its low data transmission rate, attenuation and refraction of signals. Optical light within the blue to green band has been sought as an option for underwater transmission.Characterizing the signal response of the transmitted noiseless and noisy signals is explored, especially for surface-tounderwater transmission. 5mm super bright LEDs allow only a transmission of 0.58 meter for blue and green colors for noiseless air transmission, and transmission requires the use of a convex lens placed in front of the transmitter because of the convergence of light rays. This concept paved way for a low-cost optical transmitter. For the noisy signal transmission in air, for 1 Mbps of binary data, is mixed with 250 kHz of noise, the signal can´t be decoded at an SNR of 10 dB, as compared to the signal mixed with 3 MHz of noise. On the other hand, transmission for surface-to-underwater is tested. It was confirmed that blue light attenuates less than green light for all SNR values, and faster surface water movements attenuate more, based on the received signals´ BER. Turbidity and luminous intensity also play a role in signal transmission. A very small amount of particle (milk powder or dust) mixed to water is enough for light not to pass through the receiver, even though the data being transmitted is a noiseless one.