## 7 Results and Discussion  
In this section, we focus on the BER performance versus the transmission distance and number of active users and investigate the effect of the type of water, type of modulation scheme, operating wavelength, multiplicity parameter, aperture area, and WMPC parameters. Furthermore, EVM and OSNR are compared in these results for their different coding schemes. Figure 7 presents the BER performance versus the transmission distance for the OOK-OCDMA and 2-DPPM-OCDMA systems for different types of water at receiver apertures of 400 nm and a 0.01 m\({}^{2}\) receiver aperture. From this figure, we can observe that the 2-DPPM modulation scheme almost outperforms the OOK modulation scheme, and the system can communicate over a range of 17 m, 15 m, and 7.5 m for the type-1 pure seawater with C = 0.03, type-2 ocean clear water with C = 0.38, and type-3 unclear ocean water at C = 3, respectively, at  
\begin{table}
\begin{tabular}{c c} \hline
**Parameter** & **Description** \\ \hline \multirow{4}{*}{\(P_{Ul}(u)\)} & Probability distribution function of the active users in all groups, \\  & \(P_{Ul}(u)=\frac{\left(2P(P-1)\right)\left(2P-2\right)}{\left( \begin{matrix}N-u \\ u-1\end{matrix} \right)}\) \\  & Random vector defining the amount of interference, \\ \(l\) & \(l=(l_{0},\;l_{1},\;\ldots,l_{M-1})l\), \(l_{i}\) is a random variable representing the number of \\ \(w\) & \(\begin{matrix}\text{C}\text{v}\text{e}\text{v}\text{e}\text{v}\text{e}\text{v} \text{e}\text{v\(10^{-9}\) BER. In the case of type 3, the transmission distance was incomparable to those of the other two types owing to the large amount of attenuation that occurred. The effect of the operating wavelength is presented in Figure 8 in the transmission distance for OOK-OCDMA and 2-DPPM-OCDMA in the case of type-1 pure seawater with C = 0.03 at a 0.01 m\({}^{2}\) receiver aperture area. In this figure, we observe that the best communication distance is 460 nm in the blue-green region, which outperforms the results at 400 nm and 600 nm. At a \(10^{-9}\) BER performance, when the operating wavelength is 460 nm, the system can communicate over a range of 18 m compared to the 5.5 m transmission distance at 600 nm. The effect of the receiver aperture area is presented in Figure 9, which shows the BER performance versus transmission distance for the OOK-OCDMA and 2-DPPM-OCDMA systems at 460 nm in pure seawater. When the receiver aperture area increases, the receiver field of view increases, and more optical power can be received, which allows the system to communicate over a longer transmission distance. In Figure 9, when the receiver aperture increased to 0.05 m\({}^{2}\), the system could communicate over 22 m compared to 18 m for a 0.01 m\({}^{2}\) receiver aperture area at \(10^{-9}\) BER performance. From the above results, we can conclude that the M-DPPM is a better modulation scheme than the OOK. In the following results regarding how we can increase the transmission distance underwater, the effect of the coding and system multiplicity must be taken into consideration. Figure 10 presents the 2-DPPM/WMPC-OCDMA system BER performance versus the transmission distance for pure seawater, with C = 0.03, at 460 nm, receiver aperture area of 0.05 m\({}^{2}\), and different values of the WMPC prime number P. The variation in the prime number P varies the code sequence length and code weight, and the increase in P increases the code weight and consequently increases the optical power received. This also enhances the BER performance and increases the transmission distance. Figure 7: BER performance versus the transmission distance of OOK-OCDMA and 2-DPPM-OCDMA systems for different types of water at 400 nm and receiver aperture of 0.01 m\({}^{2}\). Figure 8: BER performance versus the transmission distance for OOK-OCDMA and 2-DPPM-OCDMA systems for pure seawater, with C = 0.03 at a receiver aperture of 0.01 m\({}^{2}\) and different wavelengths.