## 5 Conclusions  
The RoF system essentially involves a transmission of analogue signals. It distributes RF signals from CS to BS directly at radio carrier frequency. RoF offers low attenuation with broad bandwidth. It has the advantage of an immunity system to the electromagnetic interference. A roof system employing WDM technique (WDM-RoF) was simulated using OptiSystem simulation software V.13. WDM can be considered the best method used in RoF. WDM allows transmission of multiple signals  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Fibre** & \multicolumn{2}{c}{**BER**} & \multicolumn{2}{c}{**Q-Factor**} & \multicolumn{2}{c}{**Eye Diagram**} \\ \cline{2-7}
**Length** & **Without** & **With Amp** & **Without** & **With Amp** & **Without** & **With Amp** \\ \hline
5 km & \(1.1009\times 10^{-10}\) & 4.37 \(\times 10^{-12}\) & 2.4347 \(\times 10^{-9}\) & 4.939 \(\times 10^{-11}\) & 1.918 \(\times 10^{-8}\) & 4.56 \(\times 10^{-10}\) \\
20 km & 6.3046 & 6.54 & 5.81 & 6.42 & 3.53 & 6.30 \\
60 km & 0.00027 & 0.0276 & 0.000157 & 0.027 & 0.0000121 & 0.02745 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Comparison of the receiver performances for different fibre lengths. Amp: amplifier.  
Figure 10: BER analyzer for receiver with 20 km (**a**) and 60 km (**b**) fibre length.  
through a single fibre over large area and can exploit the fibre network bandwidth. In addition, WDM allows the increase of optical fibre capacity compared to simple point to point linking, which only allows a single wavelength to be carried.  
For modulating optical sources, an electrical signal was used, with the modulated signal executed through an optical fibre to the receiver side. By directly modulating the signal to the optical fibre, the power consumption could be reduced, while the radio carrier frequency remained high on the BS at antenna side. Moreover, power consumption could be reduced with a simple radio station. The complex devices and equipment were preserved at the CS.  
For the WDM-RoF system with different fibre lengths, the result showed that the BER was \(1.10\times 10^{-10}\), and the Q-factor was 6.30. The sample result of the eye diagram was \(2.585\times 10^{-5}\). This system obtained a good result because the BER was less than \(10^{-9}\), and the Q-factor was more than 6.  
The utilisation of EDFA amplifier in this system creates a lot of advantages. It provides low noise figures and has independent polarisation, the most important of which is the large dynamic range. The amplifier has a quite large power transfer efficiency and comparatively flat gain. Accordingly, it can be considered very suitable for use in long distance communication. The compensation of the effects of attenuation and scattering losses with the use of EDFA is greatly explained, which leads to an improvement in the performances of the WDM-RoF system, including the BER and Q-factors, and an increase in the length of the link.  
A.H.A. designed the study, investigations and performed the data analysis. supervised the program of study and provided specialist technical knowledge essential for the completion of this work. A.D.F. provided direction and oversight of the developments needed for the implementation of the Optisystem execution as well as arrangement of the manuscript. All authors discussed the results and contributed to producing the final manuscript. This research received no external funding. The authors declare no conflict of interest.