## 3 Simulation Setup and Results
### Feasibility of the Proposed Bi-OCDMA
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Parameter** & **Value** \\ \hline \multirow{4}{*}{Global} & Bit rate & \(10^{9}\) bits/s \\ \cline{2-3}  & Sample rate & \(64.10^{10}\) Hz \\ \cline{2-3}  & Number of samples & \(4096\) \\ \cline{2-3}  & Sensitivity & \(-100\) dBm \\ \hline \multirow{4}{*}{CW laser} & Linewidth & \(10\) MHz \\ \cline{2-3}  & Power & \(0\) dBm \\ \cline{2-3}  & Azimuth & \(45\) deg \\ \cline{2-3}  & Noise threshold & \(-100\) dB \\ \cline{2-3}  & Frequency & \(1546\)... \(1568\) nm (\(\lambda_{1}\)... \(\lambda_{12}\)) \\ \hline Electrical bias & Bias & \(1\) \\ \hline Electrical gain & Gain & \(0.5\) \\ \hline Phase modulator & Phase deviation & \(180\) degrees \\ \hline \multirow{4}{*}{FSO channel} & Range & \(50\)–\(500\) m \\ \cline{2-3}  & Transmitter aperture diameter & \(5\) cm \\ \cline{2-3}  & Receiver aperture diameter & \(20\) cm \\ \cline{2-3}  & Beam divergence & \(2\) mrad \\ \hline \multirow{4}{*}{Uniform FBG} & Bandwidth & \(125\) GHz \\ \cline{2-3}  & Reflectivity & \(0.99\) \\ \cline{2-3}  & Noise threshold & \(-100\) dB \\ \hline \multirow{4}{*}{Avalanche photodetector} & Gain & \(3\) \\ \cline{2-3}  & Responsivity & \(1\) A/W \\ \cline{2-3}  & Ionization ratio & \(0.9\) \\ \cline{2-3}  & Dark current & \(10\) nA \\ \cline{2-3}  & Sample rate & \(32.10^{11}\) Hz \\ \cline{2-3}  & Thermal power density & \(10^{-22}\) W/Hz \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulation parameters. Figure 5 depicts the measured spectra when bit \"1\" was transmitted after passing through the FSO channel. Figure 5a shows the encoded spectra for the horizontal polarization, \(\lambda_{2}\), \(\lambda_{6}\), \(\lambda_{7}\), \(\lambda_{8}\), which were measured with light intensities of \(-30\) dBm. Figure 5b shows the encoded spectra for the vertical polarization \(\lambda_{1}\), \(\lambda_{3}\), \(\lambda_{4}\), \(\lambda_{5}\), which were measured with light intensities of \(-30\) dBm. With an optical power of \(-3\) dBm before passing through the FSO channel, the power was attenuated by approximately \(27\) dBm after transmission through the FSO channel due to the impact of atmospheric turbulence. Figure 6 presents the measured spectra before the optical signals entered the upper and lower photodetectors when data bit \"1\" was sent. Figure 6a shows the total measured spectra at the upper branch, \(\lambda_{1}\), \(\lambda_{2}\), \(\lambda_{3}\), \(\lambda_{4}\), \(\lambda_{5}\), \(\lambda_{6}\), \(\lambda_{7}\), \(\lambda_{8}\), measured with light intensities of \(-30\) dBm. Figure 6b presents the total measured spectra at the lower branch. No spectra were measured. Figure 4: Encoded spectra after polarization splitting when bit “1” was transmitted: (**a**) vertical polarization at upper side; (**b**) horizontal polarization at the lower side. Figure 5: Output spectrum after transmission over FSO channel for user data bits of “1”: (**a**) horizontal polarization; (**b**) vertical polarization. Using the same principle, when data bit \"0\" was sent, no spectral chip appeared at the upper branch, and eight spectral chips were measured at the lower branch, the electrical subtraction between the upper and lower branches resulted in negative signal amplitude, representing the negative parts \"\(-\)1\" of the bipolar scheme. From Figure 6a,b, eight spectral chips appeared at the upper branch, and no spectral chip was observed at the lower branch; the electrical subtraction between the upper and lower branches resulted in positive signal amplitude, representing the positive parts \"+1\" of the bipolar scheme. Further verification was undertaken by transmitting a series of user data bits alternating between bit \"0\" and \"1.\" Figure 7a,b illustrates the user's information generated from PRBS, which generated a binary bit sequence between bit \"0\" and \"1\" with the corresponding received bipolar signals from the proposed Bi-OCDMA scheme, respectively. The MAI cancelation features were evaluated using the mismatch scenario.