# Investigation of the Scattering Noise in Underwater Optical Wireless Communications
## 5 Simulation Results  
Table 1 shows three different water parameters of the albedo coefficient \(\omega_{0}\) and the attenuation coefficient \(c=a+b\), where \(a\), \(b\) are absorption and scattering coefficients, respectively. These parameters are adopted to simulate the underwater channel for different water types using MC simulation and the results are used to determine the scattering noise coefficient for different water types. All the key system parameters adopted in the simulation of the proposed scheme are given in Table 2. Note, simulation is done in Matlab, and the MC approach is used to determine the IR of the channel. The laser is modelled by solving the rate equations as [32]. Two telescopes are considered and modelled in MC. At the Tx side, a telescope is used to collimate the light, where the incoming light beam is randomly distributed based on both the beam divergence and the beam width. At the Rx side, a second telescope is used to focus the light on the photodetector, with the generated photocurrent \(I=PR\), where \(P\) and \(R\) are the received optical power and photodetector's responsivity, respectively. Following optical to electrical conversion, the output of the transimpedance amplifier \(V=GI\), where \(V\) and \(G\) are the output voltage and the gain of the amplifier, respectively. The electrical signal is then passed through a 6 th order low-pass Butterworth filter and a decision circuit (i.e., a threshold detector) to regenerate the transmitted data stream. The BER is modelled as in [32], and details of all the noise sources adopted here are given in [25]. Figure 2 illustrates the IR for the clear, coastal, and harbor waters for the link spans of 50, 20, and 4 m, respectively. Note, these link distances are selected for better illustration of the effect of scattering. In dirtier waters or longer transmission link spans, the propagating \begin{table}
\begin{tabular}{c c c} \hline \hline
**Water Type** & \(c(\lambda)(m^{-1})\) & **Albedo (\(\omega_{0}=b/c\), \(b=\) Scattering Coefficient)** \\ \hline Clear & 0.151 & 0.245 \\ Coastal & 0.398 & 0.55 \\ Harbor & 2.17 & 0.83 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Water Parameters. photons will experience a higher degree of scattering (i.e., dispersion) and attenuation, thus leading to increased BER. Figure 3 shows the scattering noise coefficient \(\kappa\), which is mentioned in (10), as a function of the link range for the three types of waters based on the parameters in Table 1. \(N\) and \(N^{\prime}\) are determined using MC simulation. Note, \(\kappa\) increases with the transmission link spans and \(b\), which is the highest for the harbor water, where more photons experience scattering. Figure 4 depicts the BER performance as a function of the transmission distance for the proposed UOWC system with and without the scattering noise and for three types of waters. As shown in Figure 4, the scattering noise results in increased BER for all three types of waters. However, this effect is less pronounced for the clear water compared with the \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Laser wavelength (\(\lambda\)) & 517 nm \\ Laser beam divergence & 0.75 mrad \\ Beam width & 0.001 mm \\ Optical power & 50 mW \\ Data rate & 500 Mbps \\ Low pass filter bandwidth (\(BW\)) & 300 MHz \\ Photodetector responsivity (\(R\)) & 0.34 A/W \\ Gain of amplifier (\(G\)) & 600 V/A \\ Rx’s field of view & 180\({}^{\circ}\) \\ Radius size of aperture & 10 cm \\ \hline \hline \end{tabular}
\end{table} 
Table 2: System Parameters. Figure 3: The scattering noise coefficient(\(\kappa\)) against the link distance for clear, coastal and harbor waters. Figure 2: The impulse responses for three types of water: clear (50 m), coastal (20 m) and harbor (4 m). coastal and harbor waters. This is mainly due to the coefficient, which is lower for the clear water, see Figure 4a.