## 8 Fourth, Fifth and Sixth Generations
#### Using FSO Links Only in 5G Communication  
As floating BSs will be playing an important role in transmitting data in 5G FSO networks, [PERSON] et al. [248] propose an atmospheric turbulence suppression algorithm that utilizes avalanche photodiode adaptive gain control (APDAGC) that transmits laser beam that improves the performance of the FSO link as atmospheric disturbance affect its performance directly. Results show the outstanding performance of the APDAGC in terms of BER and intensity fluctuation. In addition, it can be on an airship platform for 5G FSO data transmission. All the graphs confirm that adaptive gain control performs better than fixed gain control; the actual BER is better than the theoretical calculation result. In terms of numbers, the established 5G two-way FSO link provides feasibility for the air platform BS to transmit 2.5 Gbps laser signal from airship to ground with 854 and 149 Mbps downlink and uplink transmissions, respectively. However, [PERSON] et al. [249] analyze the performance of a 16 \(\times\) 10 Gbps WDM PSO system for the execution of 5G communication in various regions in India such as the hilly, plain, coastal, and desert regions. The proposed project utilizes digital signal processing and OFDM to weaken the channel induces limitations. Furthermore, it has EDFA with optimized gain characteristics. Results confirm that the link can be 10.75 km with 10\({}^{-9}\) BER in coastal areas such as Chennai with weak weather disturbances. Contrastingly, in plain and desert areas, the FSO link of ranges 6.53 km and 7.85 km have the same BER of 10\({}^{-9}\). However, in hilly areas the FSO link is only 5.3 km. The performance of the system is \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **4G** & **5G** & **6G** \\ \hline Peak Data Rate & 1 Gbps & 10 Gbps & 1 Tbps \\ \hline Technology & LTE, Wi-max & IPv4 & IPv6 \\ \hline End-To-End Latency & 100 ms & 10 ms & 1 ms \\ \hline Satellite Integration & No & No & Fully \\ \hline Artificial Intelligence & No & Partial & Fully \\ \hline Driverless Vehicle & No & Partial & Fully \\ \hline \multirow{2}{*}{Haptic} & No & Partial & Fully \\ \hline Mobility & 350 km/h & 500 km/h & 1000 km/h \\ \hline \multirow{2}{*}{Connection Density} & 10\({}^{5}\) devices & 10\({}^{6}\) devices & 10\({}^{7}\) devices \\  & /km\({}^{2}\) & /km\({}^{2}\) & /km\({}^{2}\) \\ \hline Maximum Frequency & 6 GHz & 90 GHz & 10 THz \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Comparison of 4G, 5G, and 6G systems. ideal to be used in 5G mobile networks and IoT technology as it provides high-speed connectivity. The data transmission rate of this system can reach 160 Gbps. The links in this system face some difficulties such as installing an optical fiber network in some places such as mountains which can be solved by installing FSO links with a backup hybrid RF/FSO system. [PERSON] et al. [250], experimentally propose and demonstrate a 200 Gbps FSO WDM 5G communication system based on multiwavelength directly modulated TOSA, as it simply transmits eight laser beams with different wavelengths varying from 1545 nm to 1557 nm. The authors confirm that 4-PAM modulation format enhances the system capacity. In other words, the outdoor experiment achieves 25 Gbps with 4-PAM modulation. Furthermore, one-hop and forwarding systems are tested in terms of eye diagrams and BER, respectively, with 8 \(\times\) 25 Gbps for 50 m outdoor transmission between the two buildings. Results show clear eye diagrams and reliable BER performance for all the wavelengths in the one-hop system. However, the BER for the forwarding system varies from 1E-2 to 1E-3 for 30 min. The system performance of the system is suitable for FSO fronthaul/backhaul communication system for 5G wireless cellular networks and optical access network extension as it provides low power consumption with a channelization scheme with high link reliability. Additionally, [PERSON] et al.