## 4 Related Works and Comparison to the State of the Art
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Reference** & **Architecture** & **Application** & **RF Bands** & \begin{tabular}{c} **Modulation/** \\ **Waveform** \\ \end{tabular} & \
\begin{tabular}{c} **Transmitter** \\ \end{tabular} &
\begin{tabular}{c} **Throughput** \\ \hline \hline
[30] & - FiWi mm-wave/ & - RF & -57 GHz & -91 GHz & - OFDM &
\begin{tabular}{c} - External cavity \\ laser + in-phase \\ and quadrature \\ \end{tabular} & - 24 Gbit/s \\ \hline
[31] & - FiWi mm-wave/ & -5G & -57-64 GHz & -16-QAM & -LD + SD-MZM & - 24 Gbit/s \\ \hline
[32] & - FiWi mm-wave/ & -5G & -60 GHz & -16-QAM & -LD + SD-MZM & - Not specified \\ \hline
[14] & - Multi-user FiWi links & -5G & -Baseband -700 MHz & -OFDM, GFDM, & & \\  & - MTM & -3.5 GHz & -67 GHz & -FOFDM, M-QAM & -LD + DD-MZM & - 4.41 Gbit/s \\ \hline
[33] & - Multi-user FiWi links & -5G & -60 GHz & -QPSK & -LD + SD-MZM & - 0.6 Gbit/s \\ \hline
[34] & - Multi-user FiWi links & -5G & -28 GHz & -16- and 64-QAM &
\begin{tabular}{c} - RF combiner + \\ LD \\ \end{tabular} & - 6 Gbit/s \\ \hline
[35] & - Multi-user FiWi links & -5G & -17.6 GHz -26 GHz & -M-QAM &
\begin{tabular}{c} - LD + SD-MZM + \\ optical ring \\ resonators \\ \end{tabular} & - 21 Gbit/s \\ \hline
[36] & - mm-wave/FSO links & -
\begin{tabular}{c} Backhaul \\ /fronthaul \\ \end{tabular} & -60 GHz & -BPSK & - Bias te + LD & - 1 Gbit/s \\ \hline
[37] & - mm-wave/FSO links & -5G & -60 GHz & -16-QAM & -DFB laser + \\  & - OFDM & -MZM & -4 Gbit/s \\ \hline
[25] & - mm-wave/FSO links & -5G & -28 GHz & -16-QAM & - LD + MZM & - 1 Gbit/s \\ \hline
[18] & - RoF/FSO/Wireless links & -5G & -25 GHz & -Standard LTE & - LD + 2-MZMs & - 120 Mbit/s \\ \hline
[19] & - RoF/FSO/Wireless links & -5G & -2.12 GHz -2.6 GHz -5G NR & -SFP module & - Not specified \\ \hline
[24] & - RoF/FSO/Wireless links & -Fronthaul -Access & -24-26 GHz & -64-QAM & - Bias te + LD & - 600 Mbit/s \\ \hline
[38] & - VLC access & - Access point & - & -OOK & - Bias te + & -23 Gbit/s \\ \hline
[39] & - VLC access & - 5G & - & -OFDM, GFDM & - Bias te + & -10 Mbit/s \\  & & & & and FBMC & - Bias te + & -10 Mbit/s \\ \hline
[40] & - VLC access & - Access point & - & - DCO-OFDM & - Bias te + & -6.9 Gbit/s \\ \hline \hline \multirow{6}{*}{This work} & - FiWi multi-user & \multirow{6}{*}{-700 MHz} & \multirow{6}{*}{-700 MHz} & \multirow{6}{*}{-700 MHz} & \multirow{6}{*}{-700 -10 + SD-MZM} & \multirow{6}{*}{-182.8 Mbit/s} \\  & mm-Wave/RoF link & & -700 MHz & & & \\ \cline{1-1}  & - Parallel FiWi and FSO & -4G & -3.5 GHz & -M-QAM & -LD + SD-MZM & -1.61 Gbit/s \\ \cline{1-1}  & links & -5G & -26 GHz & -LTE standard & -LD + DD-MZM & -1.4 Gbit/s \\ \cline{1-1}  & - RoF/FSO-based link & & -38 GHz & -5G NR standard & - Bias te + LED & -218 Mbit/s \\ \cline{1-1}  & -VLC access & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: State of the art on optical-wireless techniques for 5G radio access network. Multiple works have reported a hybrid mm-wave and FSO fronthaul aimed at increasing system reliability. The FSO and mm-waves links can operate in distinct architectures, namely simultaneous transmission for increased throughput in parallel with switchable transmission and a cascade system with FSO followed by a wireless link. [PERSON] et al. reported a hybrid system that simultaneously transmitted the same data over both links, namely an FSO at 1550 nm and mm-waves at 60 GHz [36]. The link selection was based on SNR for both approaches in accordance with decision thresholds aimed at evaluating BPSK transmission in a turbulent channel. [PERSON] et al. presented a hybrid FSO and mm-wave link for 5G backhauls operating at 1553.96 nm and 60 GHz, respectively. The link option was based on maximum-ratio combining (MRC) and was evaluated in terms of EVM\({}_{\text{RMS}}\) for a 16-QAM signal in turbulent, fog, and rain conditions [37]. Additionally, the authors in [25] reported a hybrid 1550 nm FSO link cascaded with a 28 GHz RF link for 5G backhaul and fronthaul applications.