# WON-OCDMA System Based on MW-ZCC Codes for Applications in Optical Wireless Sensor Networks
## 4 Simulation Results  
During the simulation, it was assumed there are four communication data channels coexisting with two video surveillance transmitters and two sensing points transmitters. Based on the MW-ZCC codes, code-weights of 4, 2, and 1 were assigned for video, data and sensing services, respectively. Used codes and associated wavelength code carriers are presented in Figure 2. The system performance was simulated using OptiSystem version 12 software, and default values were used for the optical and electrical components.  
Three different vibration frequencies (see Table 1) monitored by two sensor nodes N1 and N2 were used to demonstrate the performance of the proposed system shown in Figure 1.  
Figure 1: Diagram of WON-OCDMA hybrid system for video surveillance and vibration sensing monitoring.  
Figure 2: Codes composition for the proposed WON-OCDMA system for video surveillance, data and vibration services.  
The bit rate for data and video services was set to 1.25 Gbps to follow the ANSI T1.105 standard of OC-24. The lasers power for each wavelength chip was set to 0 dBm. The bandwidth for AWGs at the vibration sensing points and FBGs at the monitoring side was considered as 50 GHz. The Mach-Zehnder modulator extinction ratio was 30 dB, and the noise figure for the optical amplifier was 4 dB. The WON transmitter and receiver aperture diameter were set to 5 and 20 cm, respectively. The PIN photodetectors were used with responsivity was 1 A/W and thermal noise of \(10^{-22}\) W/Hz. In the WON channel, the assumed attenuation was set constant at 4 dB/km. The performance of the system was evaluated for WON affected by moderate turbulence (case when atmosphere index refraction structure is \(10^{-14}\) m\({}^{-2/3}\)[32]). The received power from sensing nodes N1 and N2 in Experiments 1 to 3 is shown in Figure 3a-c, respectively. The plotted RF signals are photodetector responses to received optical signals from two vibrations sensing nodes after 2 km transmission in WON under medium turbulence. Data represent weak, medium and high-level vibrations with frequencies of 68.1, 140.4 and 208.2 MHz, respectively. Figure 3a,b are related to scenarios in which only one sensor is affected by vibrations, while in Figure 3c both sensors are simultaneously affected (i.e., modulated). In all three scenarios, video data transmissions were active. By comparing those three plots, it can be seen that the signals from other sensors and video surveillance data have a negligible effect on the quality of retrieved signal for individual vibration sensors.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Node** & **Exp1** & **Exp2** & **Exp3** \\ \hline N1 & 70 MHz & 0 MHz & 210 MHz \\ N2 & 0 MHz & 210 MHz & 140 MHz \\ \hline \hline \end{tabular}
\end{table}
Table 1: Vibration frequencies monitored by nodes N1 and N2.  
Figure 3: RF signal received from nodes N1 and N2 in experiments 1–3 (**a–c**) indicated in Table 1.  
Example of SNR of the signal s from a sensing node N2 under conditions depicted in Figure 3c received over WON as a function of transmission distance is shown in Figure 4. The green line is the detectability limit. Maintaining an SNR of 15 dB, which is considered as the minimum recoverable value [6].  
Example of received vibration signal (210 MHz and 140 MHz) from two sensing nodes N1 and N2, respectively after 3.2 km transmitted in WON with moderate turbulence is depicted in Figure 5. The eye diagrams for the worst-case scenario data and surveillance video are shown in Figure 6. After 3.2 km transmission, the BER values for data and video are \(10^{-9}\) and \(10^{-13}\), respectively. The signals from the vibration sensing were also retrievable at this distance with SNR of 15.4 and 16.1 dB for node N1 and N2, respectively.  
Figure 4: Example of SNR of the received signal from sensing none N2 as a function of transmission distance. The green line is the detectability limit.  
Figure 5: Example of received RF signal from sensing nodes N1 and N2 after 3.2 km transmitted in WON with moderate turbulence.