## 5 Results and Discussion  
Several scenarios were designed to perform a set of experiments to evaluate the performance of LED-based underwater wireless communication considering the Red Sea parameters. A comparison with other reported works in the literature was discussed whenever possible. The results and discussion of optical transmission and resulting power at the receiver include: (i) baseline measurements, (ii) salinity effect, and (iii) turbidity effect. 1. Baseline: First, the light transmission was tested in an empty tank (without water), and the operation of all components was verified. The tank was filled with pure water (distilled water) as the baseline. Several measurements of light power were taken at different transmission distances (100, 80, 60, 40, and 20 cm). Fifty readings were taken at each point, and an average of all readings was considered as the output for better accuracy. Figure 5 shows that the received power through pure water is higher than that through air (empty tank). This result was expected due to the total internal reflection from the water-air surface occurring, increasing the amount of light collected by the receiver. This result is consistent with Ref [22]. [PERSON] et al. reported using four different types of light sources, including white, green, and yellow LEDs, and a red laser LD [14]. The underwater link distance is plotted against the normalized received power from 0 cm to 50 cm with a 10 cm gap scale. It is seen that as the underwater link distance increased, the received power of the optical signal from all the light sources decreased. When compared to LED, laser diodes produced light with a normalized intensity that was at least 41% higher. Because the light beam produced by a laser diode is focused and highly collimated, it can produce more power than an LED [23; 24]. For the same transmission distance of 50 cm, the received power of the white LED signal declines by 85%, whereas in the present work, only 10% was lost. This is due to the high-power white LED used in our experiment which translates into a high intensity of transmitted light. A much higher light intensity of at least 41% is produced by the red laser diode as compared to the used LEDs. A decline of approximately 35% is observed for the red LD, compared to an approximately 30% decline when using our white LED. Figure 5: Comparison of received power with different salinity at different transmission distances. Effect of salinity: The second scenario was to investigate the effect of salinity on the system; salt with different concentrations was added to pure water, as the minimum salinity of the Red Sea was 36 g/L, and the maximum salinity was 40 g/L. Salt concentrations of 10, 20, 30, and 40 g/L were used in this experiment. The relationship between the received power and various salt concentrations at different transmission distances is shown in Figure 5. This shows that salinity affects the performance of the LED-based UWOC link as the received power decreases with an increase in salinity. For example, at a transmission distance of 1 m, the power loss increased from 3% to 53% for 10 and 40 g/L, respectively. Moreover, the received power decreased with link length. It is also observed in Figure 5 that the received power at maximum salinity at a transmission distance of 1 m is 50% less compared to the pure water channel. These results suggest that the transmission for 1 m was of high quality and successful even at the highest salinity. In another reported work [15; 16], a 450 nm blue LD is used; the present findings are consistent with the UOWC investigation for transmission distances of 2 m and 200 m. The authors demonstrated that the received power gradually decreased as the salinity of the water channel increased. The results showed that at less than 40 cm distance, salinity of 35 g/L can block more than 90% of the laser's power [18]. It is concluded that the transmission depth for saline water channels is limited to approximately 60 cm [19].