## 6 Conclusions  
In this paper, we proposed and demonstrated a novel hybrid MMW and FSO architecture with ADCT and cc-HARQ techniques. We investigated the outage and throughput performances of the system under atmospheric turbulence influence. 10-Gbaud QPSK data were experimentally transported, and the MRC algorithm used at the receiving end fully exploited the complementary channel response of MMW and FSO links. The BER and outage probability performance improvements were tested and verified under either clean air or different turbulence intensity conditions. We provided a theoretical analysis and experimental demonstrations to validate the effectiveness of our approach. A closed-form expression for the outage probability and throughput of the RF/FSO system, considering the characteristics of atmospheric turbulence in the FSO link, was also obtained. The relevant results indicate that there is great potential for using hybrid FSO/MMW links for spatial communication in the future.  
Conceptualization, J.J. and B.D.; methodology, J.J., B.D. and J.Z.; software, Y.L., B.D. and C.H.; validation, Y.L. and B.D.; formal analysis, Y.L., B.D. and P.L.; investigation, Y.L., B.D. and P.L.; resources, J.J. and J.Z.; data curation, Y.L. and C.H.; writing--original draft, Y.L.; writing--review and editing, J.Z.; visualization, Y.L.; supervision, X.T., J.S., N.C. and J.Z. All authors have read and agreed to the published version of the manuscript.  
This work is partially supported by National Natural Science Foundation of China (62235005, 62171137 and 61925104) and the Natural Science Foundation of Shanghai (212R1408700).  
\begin{table}
\begin{tabular}{c c c c c c} \hline \multicolumn{2}{c}{**Intensity**} & \multicolumn{4}{c}{**Strong**} \\ \hline \hline \multicolumn{2}{c}{\(\boldsymbol{\
abla}\)} & \multicolumn{2}{c}{**1:4**} & \multicolumn{2}{c}{**1:2**} \\ \hline \hline \multirow{2}{*}{**FEC OH**} & \multirow{2}{*}{**Strategy**} & **Calculated** & **Calculated** & **Calculated** & **Calculated** & **Chroughput** \\  & & **Outage Pr.** & **(bps/Hz)** & **Outage Pr.** & **(bps/Hz)** \\ \hline \multirow{6}{*}{5\%} & M = 1 & 2.33 \(\times\) 10\({}^{-04}\) & 1.9043 & 2.33 \(\times\) 10\({}^{-04}\) & 1.9043 \\  & M = 2 w/RF & 2.86 \(\times\) 10\({}^{-11}\) & 1.9048 & 1.95 \(\times\) 10\({}^{-21}\) & 1.9048 \\  & M = 3 w/RF & 3.53 \(\times\) 10\({}^{-14}\) & 1.9048 & 0 & 1.9048 \\  & M = 4 w/RF & 3.42 \(\times\) 10\({}^{-17}\) & 1.9048 & 0 & 1.9048 \\  & M = 2 w/RF\&FSO & 2.90 \(\times\) 10\({}^{-14}\) & 1.9043 & 1.58 \(\times\) 10\({}^{-24}\) & 1.9043 \\  & M = 3 w/RF\&FSO & 5.06 \(\times\) 10\({}^{-19}\) & 1.9043 & 0 & 1.9043 \\ \hline \multirow{6}{*}{10\%} & M = 1 & 1.12 \(\times\) 10\({}^{-04}\) & 1.8180 & 1.12 \(\times\) 10\({}^{-04}\) & 1.8180 \\  & M = 2 w/RF & 3.48 \(\times\) 10\({}^{-12}\) & 1.8182 & 0 & 1.8182 \\  & M = 3 w/RF\&FSO & 8.33 \(\times\) 10\({}^{-16}\) & 1.8182 & 0 & 1.8182 \\  & M = 4 w/RF\&FSO & 3.36 \(\times\) 10\({}^{-15}\) & 1.8180 & 0 & 1.8180 \\  & M = 3 w/RF\&FSO & 1.13 \(\times\) 10\({}^{-20}\) & 1.8180 & 0 & 1.8180 \\ \hline \multirow{6}{*}{15\%} & M = 1 & 5.10 \(\times\) 10\({}^{-05}\) & 1.7390 & 5.10 \(\times\) 10\({}^{-05}\) & 1.7390 \\  & M = 2 w/RF & 3.39 \(\times\) 10\({}^{-13}\) & 1.7391 & 0 & 1.7391 \\ \cline{1-1}  & M = 3 w/RF & 6.24 \(\times\) 10\({}^{-18}\) & 1.7391 & 0 & 1.7391 \\ \cline{1-1}  & M = 4 w/RF & 0 & 1.7391 & 0 & 1.7391 \\ \cline{1-1}  & M = 2 w/RF\&FSO & 3.14 \(\times\) 10\({}^{-16}\) & 1.7390 & 0 & 1.7390 \\ \cline{1-1}  & M = 3 w/RF\&FSO & 8.11 \(\times\) 10\({}^{-23}\) & 1.7390 & 0 & 1.7390 \\ \hline \end{tabular}
\end{table}
Table 3: The output probability and throughput at strong turbulence intensity, with different RF to FSO data rate ratios \(\Psi\), FEC overheads, and HARQ strategies.