# Mitigation of Nonlinear Distortions for a 100 Gb/s Radio-Over-Fiber-Based WDM Network
## 4 Results and Discussion  
The analytical model in Section 3 presents how NLIs, LDs and PAPR interrupt the continuity of the WDM-RoF system and mitigate using the proposed system. Moreover, Figure 2 explains the flowchart to show the link among analytical and simulation models. Furthermore, the management approach of NLIs, LDs and PAPR in the proposed model is explored for a different set of parameters. The impacts of NLIs, LDs, phase error (PE) and PAPR are analyzed in Figures 3-9, using simulation analysis with help of Equations (19), (21) and (25). Similarly, Equations (1) to (18), (22) to (24) and (26) to (28) are utilized for simulating the results in terms of received power, input power, transmission length, normalized signal to noise ratio and RF waves as a function of BER. To investigate the receiver's sensitivity against the received optical power, a variable attenuator is used to provide a range of received power from \(-40\) dBm to \(-20\) dBm, measured using an optical power meter (OPM). Figure 3 shows the relation of the received power and BER when transmission fiber length is varied up to 10 km. At received power levels below \(-34\) dBm, the results are recorded to be above the considered BER threshold value of 3.8 \(\times\) 10\({}^{-3}\). Moreover, it is clear from Figure 3 that the amount of NLIs, LDs and PAPR increases with the transmission distance. For a general system affected from NLIs and LDs, the results show that below 10\({}^{-5}\) BER is achieved at \(-22\) dBm received power for 10 km of fiber transmission length using 5 GHz RF signal, respectively. With the proposed solution, the same BER can be achieved with \(-30\) dBm received power thus avoiding the 8 dB penalty caused by the distortion effects. It is already discussed in the mathematical model that due to NLIs, LDs and PAPR, the transmission pulses experience phase errors (PEs). Figure 4 shows the results for 0, 2.5, 5 and 8 deg PEs in terms of normalized signal to noise ratio on the x-axis. The simulation results in Figure 4 for fiber length of 5 km show that PE affects the system performance, even with the treatment of NLIs and LDs. Considering a maximum 8 deg PE, the BER threshold requires very high SNR as compared to the lower values of the PEs. Figure 5 represents the results of the presented model at 10 km transmission length for the impact of PEs which are induced due to NLIs and LDs. The results show that phase variations extend with the transmission distance but the proposed receiver can tolerate PE of 8.0 up to 10 km of transmission distance.The proposed WDM-RoF model is analyzed using different variations of the advanced modulation formats such as non-OFDM signals with 16 QAM, 64 QAM modulation and then 16 QAM-OFDM and 64 QAM-OFDM. Figure 7 explains the results for the considered modulation formats when the transmission distance is increased up to 10 km. The improvement in performance can be observed with the use of OFDM modulation with PAPR treatment, which is not possible with high PAPR which causes saturation of the EA and supports NLIs. _Electronics_**2020**, \(9\), 1796  
Figure 3: BER with function of received power at 2, 5 and 10 km of optical fiber length. Figure 2: Performance evaluation of the proposed system based on the analytical model in Section 3. Figure 4: Normalized signal to noise ratio against BER for 0, 2.5, 5 and 8 deg phase errors (PEs) at 5 km of path cover. Figure 5: Normalized signal to noise ratio against BER for 0, 2.5, 5 and 8 deg PEs at 10 km of path cover. Figure 8 shows the BER results with respect to the input launch power into the optical fiber for a 16-QAM OFDM signal with 50 GHz channel spacing. After 10 km of optical fiber transmission, the performance improvement with the proposed treatment of NLIs, LDs and PAPR is shown as compared to the general transmission case. The performance improvement saturates around \(-10\) dBm because nonlinearities increase to a large extent afterwards as a result of the high launch power.