## 4 Energy Consumption of Different Transport Schemes
### Single Base Station Energy Consumption for Different Transport Schemes  
To quantify the energy consumption of the fiber-wireless network, we investigate the energy consumption per square meter for the transport schemes discussed in Section 2. We have previously presented a generalized power consumption model for fiber-wireless base stations [40] that supports a  
Figure 5: Error vector magnitude measured for (**a**) digitized RF-over-fiber transport and (**b**) analog RF-over-fiber transport over 20 km of fiber. © [2008] IEEE. Reprinted, with permission, from _IEEE OSA Lightwave Technology, Journal._  
variety of wireless transport schemes. Shown in Figure 6 is the conventional base station architecture based on baseband-over-fiber transmission scheme. It consists of Baseband Unit (BBU), Data Converter Unit, RF unit, Power Amplifier, Feeder, Clock Management, Power Supply and Battery Backup, and Cooling System. The power consumption of this base station can be calculated using Equation (1) and Table 1 shows the power consumption of each unit approximated using commercially available devices [40].  
\[{}^{p}{}_{BBoF}={}_{N}{}_{\text{sec}tor}\times({}^{P}{}_{TX}/{}^{\mu}{}_{PA}/{} ^{L}{}_{feeder}\,{}^{+P}{}_{BBU}\,{}^{+P}{}_{DDC/DUC}\,{}^{+P}{}_{ADC/DJC}\,{}^{+P }{}_{DPD}\,{}^{+P}{}_{RFU}\,{}^{+P}{}_{M}\,{}^{\times(1+\mu}{}_{C}) \tag{1}\]  
Based on the assumption that the power for each unit remains the same regardless of the transport scheme, the model can be further applied to analog RF-over-fiber (RFoF), analog IF-over-fiber (IFoF), digitized RF (DRFoF) and IF-over-fiber (DIFoF) schemes where the detailed base station architectures are shown in Figure 7a-d. It is also noted that in this study, the same ADC/DAC specifications were used for both DRFoF and DIFoF. The power consumption of the ADC/DAC is predominately determined by the bit resolution used which is the same for both DRFoF and DIFoF in this study.  
\begin{table}
\begin{tabular}{l c c c} \hline \hline
**Parameter** & **Estimated Value** & **Parameter** & **Estimated Value** \\ \hline Power consumption of baseband unit (P\({}_{\text{BBU}}\)) & 58 W & PA efficiency & BBoF, DIFoF, DRFoF & 25\% \\ Power consumption of & (\(\mu\)\({}_{\text{PA}}\)) & IFoF, RFoF & 15\% \\ DUC/DDC (P\({}_{\text{DUCDC}}\)) & 3 W & Transmitting power (P\({}_{\text{TX}}\)) & 40 W \\ Power consumption of & 2 W & Feeder loss & BBoF & 0.5 \\ ADC/DAC (P\({}_{\text{ADC}DAC}\)) & 2 W & (L\({}_{\text{feeder}}\)) & IFoF, RFoF, DIFoF, DRFoF & 1 \\ Power consumption of & 5 W & Power supply loss (L\({}_{\text{FS}}\)) & 0.15 \\ (P\({}_{\text{DPP}}\)) & & & \\ Power consumption of & 2 W & Cooling efficiency (\(\mu\)\({}_{\text{C}}\)) & 0.2 \\ RF unit (P\({}_{\text{RFU}}\)) & & & \\ Power consumption of & 1 W & Number of sectors (N\({}_{\text{sec}tor}\)) & 3 \\ clock management (P\({}_{\text{C}}\)) & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Parameters used in base station model.  
Figure 6: Conventional base station architecture incorporating BBoF transport scheme.  
Plotted in Figure 8 is the power consumption per base station as a function of base station transmitting power for different fiber-wireless transport schemes [40]. From the results, it can be seen that for single base station, baseband-over-fiber transport consumes the most power while digitized RF/IF-over-fiber transport exhibit an advantage in energy-saving especially at high transmitting power.