# Energy Efficiency and Coverage Trade-Off in 5G for Eco-Friendly and Sustainable Cellular Networks
## 5 Results and Discussion
cell), denoting a cell experiencing a low-traffic case; the lowest modulation rate (QPSK) supports a cell radius of 500 m. For LTE with a 10 MHz BW, this case involves 50 resource blocks (RBs) with each RB including 12 subcarriers, each subcarrier having seven symbols for normal CP, and the time of the slot set to 0.5 ms. Hence, the total number of symbols per RB is 12 \(\times\) 7 \(\times\) 2 = 168 symbols per ms. Therefore, 8400 symbols per ms are identified in this case. When 1/8 QPSK is used (2 bits per symbol), the data rate will be 2.1 Mbps for a single chain, and with 2 \(\times\) 2 MIMO (2\(T\), 2R), the data rate will be twice that of a single chain, i.e., 4.2 Mbps, for the worst case of SINR. Figure 10 shows the data rate versus cell radii, with \(P_{\mathrm{tr}}\) = 43.1 dBm and \(BW\) = 10 MHz. For a 5G mm-wave small cell with a 500 MHz BW, 694 RBs are available. LTE technology comprises a RB having 12 subcarriers with 60 kHz subcarrier space. Then, each of the subcarrier has seven symbols for normal CP and six symbols for extended CP. Both the normal and extended CP have a slot time of 0.1 ms [47]. Mathematically, it is possible to estimate the number of symbols per RB as 12 \(\times\) 7 \(\times\) 10 = 840 symbols per ms, corresponding to 582,960 symbols per ms. On the other hand, if 1/8 QPSK is deployed for edge users (2 bits per symbol with a coding rate of 1/8), the data rate is 0.146 Gbps for a single chain. Therefore, with eight antenna sectors, the data rate is 8 times that of a single chain, for a total of 1.167 Gbps. In addition, with a high-order modulation 64 QAM, the total data rate with 500 MHz BW and eight antennas is up to 22.4 Gbps. Figure 11 summarizes the data rate versus MCS and BW for eight antennas. Moreover, Figure 12 summarizes the data rate that can be achieved with various numbers of antennas for different BWs at the edge of 5G small cells. Hence, in a high-traffic case, both the LTE and 5G cells are active and serve the users in the network. However, the priority goes to the 5G small cells that can provide the minimum data rate at the edge of the 5G cell of 1.167 Gbps at 1/8 QPSK with \(BW\) = 500 MHz and eight antennas used, as shown in Figure 9. By contrast, for the low-traffic case (energy saving case), the 5G BSs are switched off, and coverage is guaranteed by the LTE BSs; the maximum data rate at the edge of the LTE cell is 4.2 Mbps (\(R\) = 500 m) at 1/8 QPSK with \(BW\) = 10 MHz and two antennas used, as shown in Figure 8. However, the 4.2 Mbps data rate during the low traffic case (11 PM to 10 AM) is acceptable because the number of subscribers that are using the network for downloading data is so low during that time. Meanwhile, the voice calls are secured with full coverage by the LTE BSs. Figure 13 shows the EE performance for LTE BSs versus the cell radii. Figure 10: Data rate versus macrocell radii, with \(P_{\mathrm{tr}}\) = 43.1 dBm, \(BW\) = 10 MHz, and 2 \(\times\) 2 MIMO. From Figure 13, the EE at the edge of the LTE cell is 7.19 kb/j, which was computed based on Equation (18), i.e., a data rate of 4.2 Mbps at 1/8 QPSK with BW of 10 MHz and two antennas used, divided by the total power consumption of the 584.12 W.  
For a 5G small cell, the EE at 1/8 QPSK with BW 500 MHz and eight antennas used is 25.06 Mb/j, as shown in Figure 14, where the data rate of 1.167 Gbps is divided by the total power consumption of 46.57 W. Moreover, Figure 15 shows EE versus the number of antennas for the different BWs at the edge of the 5G small cell. Figure 11: 5G small cell data rate versus MCS and BW for eight antennas. Figure 12: Data rate versus different BWs values for different numbers of antennas at the edge of 5G small cell. Figure 7:0 5G small cell EE versus MCS and BW at eight antennas. Figure 7:1 Energy efficiency versus cell radii, with \(P_{tx}\) = 43.1 dBm and \(BW\) = 10 MHz. Figure 7:2 Energy efficiency versus different BW values for different numbers of antennas. Finally, the energy savings achieved by the proposed method is briefly discussed.