## 6 Conclusions  
In this paper, an exact CDF expression on end-to-end SNR is provided for a dual-hop mixed RF/FSO AF system, which can be used to count the noise propagation effect in performance evaluation of OP, average BER and ergodic capacity. The numerical result reveals that the performance degradation due to the inclusion of the noise propagation is about 2-12% at 10-dB SNR depending on the transmission environments. Though the performance gap reduces below 1% if the SNR is greater than 30 dB, adequate  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & & \multicolumn{4}{c}{**HD**} & \multicolumn{4}{c}{**IM/DD**} \\ \cline{3-10}  & & \multicolumn{2}{c}{\(\delta\) = 1} & \multicolumn{2}{c}{\(\delta\) = 6.7} & \multicolumn{2}{c}{\(\delta\) = 1} & \multicolumn{2}{c}{\(\delta\) = 6.7} \\ \hline Turbulence & SNR & BER & \(\tilde{C}\) & BER & \(\tilde{C}\) & BER & \(\tilde{C}\) & BER & \(\tilde{C}\) \\ \hline \multirow{3}{*}{Weak} & 10 & 9.28 & 5.69 & 12.17 & 3.97 & 3.35 & 8.08 & 6.88 & 5.64 \\  & 20 & 3.72 & 0.46 & 3.72 & 0.27 & 1.30 & 0.90 & 2.79 & 0.55 \\  & 30 & 0.52 & 0.03 & 0.38 & 0.02 & 0.25 & 0.08 & 0.54 & 0.04 \\ \hline \multirow{3}{*}{Moderate} & 10 & 8.79 & 5.74 & 11.61 & 4.06 & 2.83 & 7.97 & 5.57 & 5.70 \\  & 20 & 3.59 & 0.47 & 4.12 & 0.29 & 1.09 & 0.92 & 2.08 & 0.58 \\  & 30 & 0.42 & 0.03 & 0.50 & 0.02 & 0.21 & 0.08 & 0.45 & 0.05 \\ \hline \multirow{3}{*}{Strong} & 10 & 7.76 & 5.83 & 10.26 & 4.25 & 2.44 & 7.82 & 4.64 & 5.71 \\  & 20 & 3.09 & 0.50 & 4.13 & 0.32 & 0.92 & 0.92 & 1.64 & 0.61 \\ \cline{1-1}  & 30 & 0.47 & 0.04 & 0.74 & 0.02 & 0.18 & 0.09 & 0.29 & 0.05 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Performance degradation percentage due to the noise propagation effect in comparison with the approximate results from \(\gamma_{a}\).  
Figure 3: Comparison of CDFs (equivalently, OP) from \(\gamma_{e}\) and \(\gamma_{a}\); \(\delta=6.7\) under weak or strong turbulence, respectively.  
evaluation on the noise propagation effect seems still important especially when an energy-limited or a multihop RF/FSO AF system is considered, which could be a future research topic.  
Built the model and did the experiments, [PERSON]-K.J.; provided an initial sketch of the proposed model, [PERSON]-[PERSON]; wrote the Introduction and about the investigations, D.K. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the research fund of Signal Intelligence Research Center supervised by the Defense Acquisition Program Administration and the Agency for Defense Development of Korea.  
The authors declare no conflict of interest.  
The following abbreviations are used in this manuscript:  
\begin{tabular}{l l} AF & Amplifying-and-forwarding \\ BER & Bit-error rate \\ CDF & Cumulative distribution function \\ DF & Decoding-and-forward \\ DGG & Double generalized Gamma \\ EGK & Extended generalized-\(K\) \\ FSO & Free-space optical \\ HD & Heterodyne detection \\ IM/DD & Intensity-modulation/direct-detection \\ MGF & Moment generating function \\ OP & Outage probability \\ PDF & Probability density function \\ RF & Radio frequency \\ SNR & Signal-to-noise power ratio \\ \end{tabular}