## 7 Results and Discussion
Figure 9: BER performance versus the transmission distance of OOK-OCDMA and 2-DPPM-OCDMA systems for pure seawater, with C = 0.03, at 460 nm and different receiver aperture areas. As shown in Figure 10, when the prime number P increases, the transmission distance increases until a certain value is reached. Above this value, the increase in P did not change the transmission distance because the system's multiple-access interference degrades the OSNR. In these results, P varied from 11 to 59, and the transmission distance varied from 45 m to 155 m. From P = 53 to 59, the change in the transmission distance was less at approximately 5 m, and it is clear from the figure when P increases above 43 at 53, 57, and 59. For more clearance, we can see that above 53, the increase in the transmission distance is slightly above 57, and the transmission distance is approximately the same. This is because when P increases, the multiple-user interference increases and reduces the OSNR, and there is no effort to increase the code parameter P.  
Figure 11 shows the BER performance versus the received optical power for the M-DPPM/WMPC-OCDMA system for pure seawater with C = 0.03, at 460 nm, receiver aperture area of 0.05 m\({}^{2}\), WMPC prime number P = 53, transmission distance 800 m, and different values of system multiplicity M. The results show that when the received optical power increases, the BER performance improves. Also, this figure shows the BER performance enhanced with the system multiplicity increase. Figure 12 presents the BER performance versus the transmission distance for the M-DPPM/WMPC-OCDMA system for pure seawater with C = 0.03, at 460 nm, receiver aperture area of 0.05 m\({}^{2}\), WMPC prime number P = 53, and different values of system multiplicity M. According to Equation (19) in Table 5, when the system multiplicity increases, the SNR increases, and the BER performance decreases, which increases the link transmission distance. However, when M increases to a certain value, the transmission distance increases at a low rate, and above this value, the transmission does not change as M increases. Figure 12 shows that when M increases from 2 to 512, the transmission distance increases from 155 m to 930 m at a BER of \(10^{-9}\). Above M = 512, the transmission distance does not change owing to degradation in the OSNR. Figure 10: BER performance versus the transmission distance of 2-DPPM/WMPC-OCDMA system 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.  
Figure 11: BER performance versus the received power of the M-DPPM/WMPC-OCDMA system for pure seawater, with C = 0.03, at 460 nm, receiver aperture area of 0.05 m\({}^{2}\), WMPC prime number P = 53, \(d=800\) m, and different values of system multiplicity M.  
Figure 12: BER performance versus the transmission distance of the M-DPPM/WMPC-OCDMA system for pure seawater, with C = 0.03, at 460 nm, receiver aperture area of 0.05 m\({}^{2}\), WMPC prime number P = 53, and different values of system multiplicity M.  
Based on the above results, we obtained the optimum system parameters for calculating the network capacity and bit rate per user. Figure 13 illustrates the BER performance versus the number of active users N for the 256-DPPM/WMPC system, while considering all the optimum parameters achieved above at different values of the coding parameter \(P\). The results showed that when \(P\) was increased from 23 to 59, the number of active users increased from 360 to 1310. Above \(P=59\), the multiple-access interference increases, and the number of active users remains the same at a BER performance of \(10^{-9}\).