## 8 Conclusions  
In this paper, a flexible and secure optical body area network based on free space optics wireless technology and a time-delayed two dimensional spectral/spatial optical code-division multiple access system is demonstrated using numerical simulations. The proposed setup consists of eight sensors mounted on the body of a patients that record their vital physiological data. The data of each sensor are secured using two dimensional double-weighted zero-cross correlation codes. After spectral/spatial encoding, the data of each signal are time-delayed and the combined optical signal is transmitted over an \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sr. No** & **Component** & **CAPEX\({}_{c}\) (S)** & **CAPEX\({}_{p}\) (S)** \\ \hline
1 & Optical combiner (1:4) & \(10\) & \(12.5\) \\
2 & Optical splitter (1:4) & \(10\) & \(12.5\) \\
3 & FSO module & \(60\) & \(15\) \\
4 & Time delay units & \(0\) & \(16\) \\ \hline \hline \end{tabular}
\end{table} 
Table 7: CAPEX required for installation of each component in the two architectures. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sr. No** & **Architecture** & **CAPEX (S)** \\ \hline
1 & Conventional & \(80\) \\
2 & Proposed & \(60\) \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Comparison of the total CAPEX for the proposed and conventional architectures. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Study** & **Sensors** & **Range** & **Link** & **Code** & **BER** \\ \hline
[2] & 4 & 0.5 km & IR, extra-body & SAC & \(10^{-9}\) \\
[4] & 5 & 8 m & VLC, extra-body & Un-coded & \(10^{-4}\) \\
[6] & 1 & 5 m & VLC, extra-body & Un-coded & \(10^{-3}\) \\
[10] & 4 & 2 m & VLC, extra-body & Walsh code & \(10^{-6}\) \\
[11] & 2 & 1.3 m & VLC, extra-body & Walsh code & \(10^{-6}\) \\
[16] & 4 & 8 m & VLC, extra-body & BPPM & \(10^{-3}\) \\ Proposed & 8 & 1-2.75 km & IR, extra-body & 2D DW-ZCC & \(10^{-9}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Comparison between the proposed work and similar past studies. FSO channel with a range of 1 km towards the medical center. The data of each sensor are decoded and recovered after photodetection at the medical center for further analysis by the medical staff. The performance of the sensors ws analyzed using bit error rate and Q-factor plots for different weather conditions while considering a log-normal channel. The effect of variations in the receiver aperture diameter and beam divergence over the bit error rate and quality factor of the received signals was evaluated as well. Secure and error-free transmission of sensor data between the transmitter and remote medical center was successfully achieved under different weather conditions. The CAPEX of the proposed architecture was analyzed and compared with a conventional 2D-spectral/spatial FSO system to determine the overall impact of introducing time-delay units on the cost of implementation. The proposed architecture is flexible, cost-efficient, secure, and compatible with the green radio trend, while fulfilling the recent recommendations of the IEEE 802.15.6 Task Group on future body area networks. [PERSON], [PERSON] and [PERSON] introduced the concept and model; F.K., [PERSON] and [PERSON] performed the simulations; F.K. wrote the paper; [PERSON] and [PERSON] proofread the paper; F.K. and [PERSON] prepared the plots and figures and validated the results; and [PERSON] supervised the project. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. The data and material generated during this study are available from the corresponding author on request. [PERSON] would like to acknowledge the support provided by KFUPM through project no. INCS 2303. The authors declare no conflict of interest. The following abbreviations are used in this manuscript: