## 6 Concluding Remarks  
In this paper, the converging wireless optical communication system based on a cooperative terrestrial and underwater FSO scheme has been analyzed in terms of the average bit-error rate. The study here presented has considered the effects of the turbulence in both atmospheric and underwater environments into system performance, modeling the scintillation induced in each medium with Malaga and Weibull statistical distributions, respectively. Hence, the effects of both channels on the overall system behavior are highlighted with closed-form analytical expressions obtained to evaluate the ABER for uncoded and coded transmissions. Thus, in some of the results shown, it is possible to intuit the predominant effect of the terrestrial or submarine environment as a function of the signal-to-noise ratio. The analytical expressions here proposed also provide a simple and efficient procedure for estimating the behavior of any coding scheme for which the bit-error-rate behavior in an AWGN channel without turbulence can be adjusted by the  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Code Rate** & **Terrestrial FSO Channel** & **Underwater FSO Channel** & **OOK-GScc** & **vw-MPPM** \\ \hline \multirow{2}{*}{\(1/4\)} & _ideal AWGN (\(\sigma_{h_{1}}^{2}=0\))_ & \(\sigma_{h_{2}}^{2}=0.0496\) & \(0.75\) & \(-0.82\) \\  & \(\sigma_{h_{1}}^{2}=2.699\) & \(\sigma_{h_{2}}^{2}=1.0652\) & \(44\) & \(39.13\) \\ \hline \multirow{2}{*}{\(1/8\)} & _ideal AWGN (\(\sigma_{h_{1}}^{2}=0\))_ & \(\sigma_{h_{2}}^{2}=0.0496\) & \(-4.19\) & \(-4.15\) \\  & \(\sigma_{h_{1}}^{2}=2.699\) & \(\sigma_{h_{2}}^{2}=1.0652\) & \(40.06\) & \(36.8\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: SNR (\(\tau_{0}\)) [\(dBs\)] for achieving an ABER of \(10^{-4}\).  
Figure 6: Analytical ABER and Monte Carlo simulation results (circles) vs. SINR \(\gamma_{0}\) for a vw-MPPM format with code rate of \(1/8\) under weak (\(\sigma_{h_{2}}^{2}=0.0496\)), weak-to-moderate (\(\sigma_{h_{2}}^{2}=0.2453\)) and strong (\(\sigma_{h_{2}}^{2}=1.0652\)) salinity-induced turbulence and different Malaga turbulence intensities in the terrestrial FSO link. Scenarios and values of irradiance variances in the underwater medium taken from acquired data presented in [68]. In solid lines, the performance of the system when only oceanic turbulence is considered is represented.  
hyper-exponential method employed here. It must be noted that the proposed closed-form expressions have been corroborated by Monte Carlo simulations for different turbulence conditions and several code rates. Remarkably, the new derived expressions resulted in a valuable tool for analyzing the performance of these cooperative optical links, which involved either the effects of the terrestrial and underwater channels or the behavior of different coding techniques.  
[PERSON] and [PERSON] defined the scope of the review manuscript. [PERSON], [PERSON] and [PERSON] compiled the necessary information to elaborate this review manuscript. [PERSON], [PERSON] and [PERSON] derived the expressions and obtained the results. [PERSON] wrote the article. [PERSON], [PERSON], [PERSON] and [PERSON] reviewed and edited the manuscript. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Junta de Andalucia (research group \"Communications Engineering (TIC-0102)\").  
Not applicable.  
The authors want to thank to the Spanish Ministerio de Ciencia, Innovacion y Universidades (proyect PID2019-107792 GB-I00) for supporting this work.  
The authors declare no conflict of interest.