# Investigation of OFDM-Based HS-PON Using Front-End LiFiSystem for 5G Networks
## 3 Results and Discussions  
Our proposed LiFi HS-PON/16-QAM OFDM system was simulated using OptiSystem v.21. OptiSystem is an integrated software design suite which enables consumers to plan, \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{1}{c}{**Parameters**} & \multicolumn{2}{c}{**Values**} & \multicolumn{1}{c}{**Unit**} \\ \hline \multirow{5}{*}{CW Laser} & Frequency (DN) & 187.5,187.6, 187.7, 187.8 & THz \\  & Frequency (UP) & 195.3,195.4, 195.5, 195.6 & \\  & Input power (DN and UP) & \(-6\) & dBm \\  & Linewidth & 0.15 & MHz \\ \multirow{2}{*}{LiNb Mach– Zehnder Modulator Multiplexer} & Extinction ratio & 60 & dB \\  & Bandwidth & 15 & GHz \\ \multirow{2}{*}{Optical amplifier} & Gain & 13 & dB \\  & Noise figure & 4 & dB \\  & Length & 10–100 & Km \\  & Attenuation & 0.2 & dB/km \\  & Reference wavelength & 1550 & nm \\ Optical fiber & Dispersion & 16 & ps/nm/km \\  & Dispersion slope & 0.075 & ps/nm\({}^{2}\)/km \\  & Third-order dispersion & Yes & \\  & Group velocity dispersion & Yes & \\  & Responsivity & 1 & A/W \\ Photodetector PIN & Dark current & 10 & nA \\  & Thermal noise & \(100\times 10^{-24}\) & W/Hz \\  & Shot noise & Yes & \\  & Blue & 450 & nm \\ LED & Quantum efficiency & 0.65 & \\  & Distance & 10–20 & m \\  & Room size & \(10\times 10\times 10\) & m \\  & Transmitter half-angle & 60 & \\ LOS channel & Irradiance half-angle & 20–50 & deg \\  & Incidence half-angle & Detection surface area & 1.5–4 & cm\({}^{2}\) \\ Low-pass filter & Cutoff frequency & 37.5\(\times 10^{9}\) & Hz \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters values [27]. test, as well as simulate optical links in the transmission layer of contemporary optical networks. The proposed model is analyzed considering practical scenario under the impact of real environment conditions to deploy a practical design. In the proposed system both mathematical and the OptiSystem simulation analysis have been performed to provide the realistic values of the received outputs in terms of SNR, OSNR, BER, output power, etc. We simulated four downlink and four uplink channels operating at 187.5-187.8 THz and 195.3-195.6 THz with a 50 Gbps/channel data rate. For 5G networks, it is reported that blue LEDs are used for indoor LiFi LOS transmission. Our simulation includes both linear (e.g., optical noise, crosstalk, and fiber dispersion) and nonlinear impairments (e.g., four-wave mixing). We investigate the model's performance with respect to BER, received power, constellation diagrams, eye patterns, and optical spectra. To analyze performance, we consider different fiber lengths, system throughput, the detection surface area for LiFi channels, transmitter and receiver angles, and the indoor wireless range. In the proposed work, a minimum BER of 10 \(\times\) 10\({}^{-3}\) for LiFi systems is considered sufficient. The proposed digital coherent receivers are implemented with, most likely, forward error correction (FEC) coded sequences. FEC codes allow the recovery of considerable error bit levels to deliver an absolute digital signal over long distances and at high traffic rates. In addition, FEC enhancement utilizes decision algorithms (soft or hard) to allow an optimum net coding gain, better tolerating transmission link impairments and increasing transmission capacity (>100 Gbps) while considering a 7-35% overhead [29; 30]. Figure 5a-p depict the attained output plot foreach stage of the hybrid HSP-PON/OFDM with LiFion50 km fiber with a 10 m LiFi channel range at a 50 Gbps/channel rate for the downlink OFDM signal (187.7 THz). Figure 5: _Cont._  
Figure 6a,b indicate the optical spectra before the transmission of the proposed work for both downlink (187.5, 187.6, 187.7, and 187.8 THz) and uplink (195.3, 195.4, 195.5, and 195.6 THz) transmission channels with a 100 GHz channel spacing. Figure 7a,b represent the received optical power of different frequency signals with a fixed LiFi channel range of 10 m for downlink and uplink directions.