# Renewable Energy-Based Energy-Efficient Off-Grid Base Stations for Heterogeneous Network
## 3 System Configurations and Mathematical Model
### Simulation Setup for HOMER and Resource Scheduling  
The proposed hybrid power supply system has been focused on meeting the power consumption of the BSs of a HetNet. As a result, estimating the proper dimensions of macro, micro, pico, and femto-cell power consumption is important. The total power consumption of a BS is mainly dependent on traffic demand; we formulated the discrete power consumption considering 10 MHz bandwidth from paper [65] using the following equation. Then, on that basis, we designed and optimised the overall power generation and sharing architecture, considering the energy, cost and environmental aspects. The assumed traffic demand profile for the proposed model is shown in Figure 8.  
\[P_{BS}=\begin{cases}N_{TRX}[P_{1}+\Delta_{p}P_{TX}(\chi-1)],&\text{if }0<\chi \leq 1\\ N_{TRX}P_{sleep},&\text{if }\chi=0,\end{cases} \tag{27}\]  
where, \(P_{1}=P_{0}+\Delta_{p}P_{TX}\).  
The discrete power consumption by the macro, micro, pico, and femto cellular LTE BSs considering the 10 MHz bandwidth are obtained from [65]. It implies that a smaller BS needs lower power due to the smaller radiated power and coverage area.  
The power consumption of the BSs that is directly connected to the related loss factors, and can be calculated as [65; 66]:  
\[P_{1}=\frac{P_{BB}+P_{RF}+P_{PA}}{(1-\sigma_{DC})(1-\sigma_{MS})(1-\sigma_{ cool})} \tag{28}\]  
where \(P_{BB}\), \(P_{PA}\) and \(P_{RF}\), respectively, refer to the baseband, power amplifier and RF power consumption scaled with the transmission bandwidth.  
We first study the techno-economic feasibility of the proposed system. In the simulation setup, we assume a project duration is 20 years and the yearly interest rate is 6.75% [67]. The HOMER platform was used for this study. The system architecture of the proposed heterogeneous network is shown in Figure 9 and 10. The initial values of the main parameters are listed in Table 3.  
Figure 8: Assumed traffic profile for the simulation.  
Monte-Carlo simulation parameters has shown in Table 4. For the simulation setup of Algorithm 1, the assumed value of the parameters are shown in Table 5. The parameters for the simulation setup of Algorithm 2 are listed in Table 6.  
Figure 10: System architecture in the HOMER platform for pico (**left**) and femto (**right**) BSs.  
\begin{table}
\begin{tabular}{c l c} \hline \hline
**Components** & **Parameters** & **Value** \\ \hline \multirow{2}{*}{Resources} & Solar intensity & 4.59 kWh/m2/day \\  & Biomass available & 9 t/day \\  & Interest rate & 6.75\% \\ \hline \multirow{2}{*}{Solar PV} & Operational lifetime & 25 years \\  & Derating factor & 0.9 \\  & System tracking & Dual-axis \\  & CC & \$1/W \\  & RC & \$1/W \\  & OMC/year & \$0.01/W \\ \hline \multirow{2}{*}{BG} & Efficiency & 30\% \\  & Operational lifetime & 25,000 h \\  & CC & \$0.66/W \\  & RC & \$0.66/W \\  & OMC/year & \$0.05/h \\  & FC & \$30/t \\ \hline \multirow{2}{*}{Battery} & Round trip efficiency & 85\% \\  & \(B_{\text{SoC}_{min}}\) & 30\% \\  & \(V_{nom}\) & 6 V \\  & \(Q_{nom}\) & 360 Ah \\  & CC & \$300/unit \\  & RC & \$300/unit \\  & OMC/year & \$10/unit \\ \hline \multirow{2}{*}{Converter} & Efficiency & 95\% \\  & Operational lifetime & 15 years \\  & CC & \$0.4/W \\  & RC & \$0.4/W \\  & OMC/year & \$0.01/W \\ \hline \hline \end{tabular}
\end{table}
Table 3: Key parameters and their values for HOMER simulation setup [63; 64].  
Figure 9: System architecture in the HOMER platform for macro (**left**) and micro (**right**) BSs.