# Two-Dimensional Permutation Vectors' (PV) Code for Optical Code Division Multiple Access Systems
## 6 Proof of Concept
One part was applied to an arrangement of FBG filters that were configured in accordance with spectral signature of the encoder. For example, for user U\({}_{0,0}\), FBG filters at the top leg were configured to recover \(\lambda_{3}\) and \(\lambda_{7}\), whereas the FBG filter employed at the bottom leg was used to recover the complement of the intended signature. The output of both filter arrangements was passed through PIN photodiodes and subtracted to recover the intended spectrum with maximum auto- and minimum cross-correlation. Then, for the initial analysis, the performance of the proposed system was analyzed in terms of data rate versus bit error rate. Moreover, with an EDFA of 9 dB gain, power at the CNTs of the first remote node \(RN_{1}\) was set at 0 dBm, respectively. Figure 8 shows the eye diagrams and BER of the proposed setup at 1 Gbps and 2 Gbps of data for randomly selected nodes of \(ONT_{RN_{1}}\). It was observed that the proposed setup was well able to support high data rates of up to 2 Gbps. Moreover, analysis of the BER and eye diagrams validated the implementation setup such that BER increased with an increase in the amount of data transmitted between the OLT and ONTs' modules. This can be attributed to the fact that pulse width decreased with an increase in the data bits, which made the system more vulnerable to distortion across the medium. Consequently, a higher data rate will yield a higher BER. However, analysis showed that for an agreeable BER of \(10^{-9}\) the proposed setup was able to provide the desired performance up to 2 Gbps of data, owing to the efficient cross-correlation properties at the \(X^{th}\) code sequence and proficient design of the proposed setup that maintained a nominal signal power to yield a desired signal-to-noise ratio and, hence, BER. To further analyze the impact of the power budget on the overall performance of the setup, analysis was made at 1 Gbps of data by randomly selecting nodes at each remote node from \(RN_{1}-RN_{3}\). Moreover, through the application of nine EDFA at the transmitter module, 0 dBm, \(-3\) dBm, and \(-6\) dBm power was observed at the \(ONT_{RN_{1}}\), \(ONT_{RN_{2}}\), and \(ONT_{RN_{2}}\), respectively. Eye diagrams and BER analysis in Figure 9 show that the proposed setup was capable enough to handle the power drops at each remote node and provide desired results for an acceptable BER of \(10^{-9}\). Results' analysis also validated the proposed model, which showed a relevant decrease in the BER along with a decrease in the power each ONT of alternated remote nodes. Figure 8: Eye diagrams for downlink traffic at (a) 1 Gbps and (b) 2 Gbps. Figure 9: _Cont_. In order to analyze the impact of the switching arrangement and observe the capability of the proposed setup to handle traffic in both clockwise and counterclockwise directions, the proposed model was simulated with an optical switch after the transmitter module. Moreover, for fair analysis, the number of simultaneous users accessing the medium was reduced to \(K_{1}=4,\ K_{2}=2\) with \(N_{2}=8\). Analysis was performed at 1 Gbps of data and port 2 of the switch was initially engaged to observe the flow of traffic in a clockwise direction. In the second phase of the simulation, port 3 was engaged to analyze the flow of traffic in a counterclockwise direction to mimic a state of failure. Figure 10 shows the eye diagrams and BER analysis for the flow of traffic in both clockwise and counterclockwise directions. It is evident that the proposed setup was able to support the flow of traffic in both directions with minuscule effect on the overall performance. It can be observed that for 1 Gbps of data almost the same BER was obtained at the randomly selected ONT of \(RN_{1}\) (clockwise flow of traffic) and \(RN_{2}\) (counterclockwise flow of traffic).