# Energy Efficiency and Coverage Trade-Off in 5G for Eco-Friendly and Sustainable Cellular Networks
## 5 Results and Discussion  
This section first discusses the performance evaluation of the LTE cell coverage area optimization issue during the period when 5G BSs are switched off based on the PSO under constraints, the transmission power of the BS, the total antenna gains, the flexible BW, and the propagation environment (SINR, path loss, and fading) according to the optimization problem formula given in Equation (11) and the setup parameters listed in Table 1. The second part of the discussion focuses on the data rate that will be delivered to the UEs during 5G BSs' switching off and on, because the EE is a function of both the data rate and the total BS power consumption. The final part of this section evaluates the EE based on the proposed BSs switching-off/on model. Figures 7 and 8 describe the behavior of the LTE BSs coverage when the 5G BSs are switched off at low traffic load and the behavior of the constraints that affect the coverage, respectively. Figure 7 shows that at the start, with random particle positions and zero velocities (at iterations equal to zero), the LTE cell coverage area was 99.05%, with \(P_{\rm{LK}}\) = 43.08 \(\rm{dB_{m}}\) and \(G\) = 7.97 dB, at \(SINR\) = 1.49 dB and \(\sigma\) = 5.50 dB, as shown in Figure 6. From Figure 6, when the \(SINR\) decreased, both \(P_{\rm{LK}}\) and \(G\) increased to maintain the maximum coverage area. The simulation results demonstrated that the optimum transmitting power \(P_{\rm{LK}}\) and the antenna gain \(G\) that maintain maximum coverage at the edge (where the \(SINR\) was the lowest at \(-\)5.1 dB and where the shadowing is at 4.8 dB) are 43.1 \(\rm{dB_{m}}\) \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Item** & **Parameter** & **Acronym** & **LTE** & **Unit** \\ \hline \multirow{4}{*}{Mobile station parameters} & Thermal noise density & \(N_{o}\) & 174 & \(\rm{dB_{m}/Hz}\) \\  & Noise figure & \(N_{f}\) & 9 & dB \\  & Implementation margin & \(IM\) & 3 & dB \\  & Antenna height & \(h_{\rm{LIE}}\) & 1.5 & M \\  & Morphology & Uurban & & \\  & Propagation model & 3 GPP UMa-NLOS & & \\  & Avg. building height & \(h_{bl}\) & 20 & m \\ Propagation losses & Street width & \(W_{slt}\) & 20 & m \\  & SINR & \(SINR_{\rm{min}}\) & \(-\)5.1 & dB \\  & Shadow fading margin & \(\sigma\) & 4-8 & dB \\  & Exponent path loss & \(\alpha\) & 3.2 & \# \\ \hline \hline \end{tabular}
\end{table} 
Table 1: \(Cont.\)  
Figure 7: Behavior of the fitness function with a change in the constraint parameters. and 6.3 dB, respectively. In addition, the optimal \(BW\) is 10 MHz during the period that the 5G BSs are switched off; the optimal \(BW\) is proportional to \(P_{\rm min}\), as given in Equation (11). However, for a high data rate, a BW greater than 10 MHz can be used. In this case, the full coverage is not secure because the \(P_{\rm min}\) required is high. It is plausible that big bandwidth has the possibility of improving the EE when compared to a small bandwidth within the same size coverage area based on the premise that big bandwidth can support more resource blocks, eventually leading to a higher data rate. For the downlink (DL), i.e., from the BS to the UE, the BS typically selects the MCS based on the channel quality indicator (CQI) feedback characteristics of the UE receiver, i.e., the SINR via an adaptive link strategy. Based on assumptions made in [38], Figure 9 shows the relationship between the radius of the cell, \(P_{\rm min}\), and the MCS. The received power level is obtained from the sensitivity calculation in Equation (9), and the values of \(SINR\), \(IM\), etc., are retrieved from Table 1.  
When \(P_{\rm min}\) reduces, the MCS reduces simply because the demodulation error rate rises as a result of the rise in both the noise and interference. This analysis is of a cell radius of 500 m (edge of the LTE  
Figure 8: Behavior of the constraint parameters. Figure 9: Cell radii versus receiver sensitivity power for different MCSs, with \(P_{tx}\) = 43.1 dB\({}_{\rm m}\) and BW = 10 MHz.