## 4 Performance Evaluation  
### Optical Power Budget  
The optical power budget is analyzed to ensure that the received signal power is enough to maintain acceptable performance even though the lengths of communication links between the control center and WTs are different. The power budget for EPON specified in IEEE 802.3 ah standard is 26.0 dB in the case of 1000 Base-PX20, for both upstream and downstream traffic. The optical budget [dB] is defined as the difference between the minimum transmitter launch power (P\({}_{tx}\), dBm) at the input of the optical link, and the minimum sensitivity of the receiver (P\({}_{rx}\), dBm) at the output of optical links [17; 18; 19] as shown in Equation (1):  
\[\text{Power Budget}\ =P_{tx}-P_{rx} \tag{1}\]  
There are many sources of attenuation including splitters (\(Loss_{POS}\)), connectors (\(Loss_{conn}\)), and the fiber cable itself (\(Loss_{fiber}\)). The total optical power loss (\(P_{Loss}\)) of optical link given in [dB] is calculated as shown in Equation (2):  
\[P_{Loss}=\sum Loss_{POS}+\sum Loss_{Conn}+\sum Loss_{Fiber} \tag{2}\]  
Table 2 shows the EPON specification according to IEEE 802.3 ah standard. The component insertion loss is shown in Table 3. We considered the fiber attenuation is 0.4 dB/km, and the connector loss is 0.2 dB. Passive optical splitter (1 \(\times\) 2) insertion loss is 0.4 dB for a split ratio of 5.95, while the insertion loss is 3 dB for split ratio of 50:50.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**EPON** & **OLT** & **FF (km)** & \begin{tabular}{c} **Number** \\ **Primary POS** \\ \end{tabular} & \begin{tabular}{c} **Number** \\ **Secondary POS** \\ \end{tabular} & \
\begin{tabular}{c} **Number** \\ **Other POS** \\ \end{tabular} &
\begin{tabular}{c} **DP (km)** \\ \end{tabular} \\ \hline A & 1 & 5 & 1 (1 \(\times\) 2) & 12 (1 \(\times\) 2) & - & 11 \\ B & 1 & 5 & 1 (1 \(\times\) 2) & 2 (1 \(\times\) 6) & - & 31 \\ C & 1 & 5 & 1 (1 \(\times\) 2) & 4 (1 \(\times\) 4) & - & 19 \\ D & 1 & 5 & 1 (1 \(\times\) 2) & 2 (1 \(\times\) 4) & 6 (1 \(\times\) 2) & 17 \\ E & 1 & - & 1 (1 \(\times\) 12) & - & - & 36 \\ \hline \end{tabular}
\end{table}
Table 1: Network elements of small wind power farms (WPF) (unprotected).  
\begin{table}
\begin{tabular}{c c c} \hline
**Parameter** & **Data Rate** & **Power Budget** \\ \hline  & 1.25 Gbps & PX-20U 26 dB \\ EPON & (D and U) & PX-20U 26 dB \\  & 1000 Base-PX20 & PX-20U 26 dB \\ \hline \end{tabular}
\end{table}
Table 2: IEEE STD 802.3 EPON specifications.  
\begin{table}
\begin{tabular}{c c} \hline
**Component** & **Attenuation** \\ \hline Fiber & 0.4 dB/km \\ \hline Connector & 0.2 dB \\ \hline  & 1 \(\times\) 2 (5\%:95\%) \(\rightarrow\) 0.4 dB \\ \cline{2-3} Splitter & 1 \(\times\) 4 \(\rightarrow\) 6.0 dB \\ \cline{2-3}  & 1 \(\times\) 8 \(\rightarrow\) 9.0 dB \\ \cline{2-3}  & 1 \(\times\) 16 \(\rightarrow\) 12.0 dB \\ \hline \end{tabular}
\end{table}
Table 3: Component insertion loss.  
Figure 8 shows the total optical path loss calculation for the five different configurations. The highest optical path loss value represents the farthest turbine, while the lowest value represents the nearest turbine. For example, the highest optical path loss value is about 20.2 dB for WT12 in architecture (C), while the lowest value is about 6.6 dB for WT1 in architecture (A). In architecture (A), with 1 km between WTs, fiber attenuation is 0.4 dB, connector loss is 0.4 dB and POS (\(1\times 2\)) has insertion loss of 0.4 dB. This is the reason why the total optical path loss is growing linearly.  
Figure 8: Total optical path loss for different architectures.  
The analysis of optical power budget shows that architecture (A) offers a lower optical path loss among other architectures due to a small insertion loss of POS (\(1\times 2\)). However, architecture (B) has a higher optical path loss due to a higher splitting ratio and length of fiber cables. Architecture (C) and architecture (D) combine the advantage of both configuration (A) and configuration (B).