# Energy Efficiency Analysis of MIMO Wideband RF Front-End Receivers
## 4 Results and Discussions
This indicates that the very low power consumption of the LNA design in [12] plays an important role to maximize the EE in short transmission distances, while the lower noise figure of the LNTA from [17] becomes more important when the distance increases, since it allows alleviating the transmitted power of the PA, at the transmitter side. Complementing the analysis, the importance of the spatial diversity brought by the multiple antennas becomes more evident in Figure 3(b), which increases the number of antennas to \(N_{\rm t}=N_{\rm r}=4\). As we observe, similar conclusions can be drawn for the AS scheme, where the LNA becomes more energy efficiency for up to \(d\leq 220\) m. However, when submitted to the SVD scheme, the LNA presents better performance than the LNTA. The performance difference decreases when the transmission distance increases. Next, Figure 5 shows the energy efficiency of the AS scheme as a function of the number of antennas, considering \(N_{\rm t}=N_{\rm r}\) and \(d=\{50,400\}\) m, for the LNA and LNTA architectures. As we observe, when \(d=50\) m the LNA outperforms the LNTA in terms of energy efficiency, while this conclusion inverts for \(d=400\) m. As previously mentioned, the noise figure of the selected LNTA is lower than that of the LNA counterpart, which becomes more important when the distance increases, regardless of the number of antennas. In addition, we also observe that the energy efficiency increases with the number of antennas up to a saturation level. Figure 4: Energy efficiency of SISO, AS and SVD schemes, considering the LNA [12] and LNTA [17] architectures. For the SVD scheme, on the other hand, there is an optimal number of antennas to maximize the energy efficiency, which depends on the transmission distance, as depicted by Figure 6 for \(d=\{50,400\}\) m. Similarly as for the AS scheme, the LNA outperforms the LNTA for short transmission distances. When \(d\) increases, the LNTA performs better for a reduced number of antennas (less than 4). Improving the spacial diversity allows the LNA to surpass the LNTA, even presenting a worst noise figure. For the SVD scheme, the number of antennas determines the number of receivers. Hence, power consumption becomes a key metric in the energy efficiency performance. Finally, Figure 7 plots the energy efficiency of the AS and SVD schemes as a function of \(N_{\rm t}=N_{\rm r}\), comparing the LNTAs from [17] and [18], for \(d=400\) m. As we observe, the LNTA designed in [17] is always more energy efficient with the AS scheme, in which a single pair of RF chains is active for communication. However, there is a trade-off between [17] and [18] for the SVD scheme when the number of antennas increases. With a few antennas (less than 3), the energy efficiency using [17] is higher, while it is outperformed by [18] with more antennas. By taking the parameters of Table 1 into account, we observe that the LNTA in [17] has very low noise figure and high power consumption, with \(F_{\rm rx}=1.6\) dB and \(P_{\rm rx,FirstBlock}=41.88\) mW. On the other hand, the design in [18] has very low power consumption at the expense of a higher noise figure, with \(F_{\rm rx}=7.5\) dB and \(P_{\rm rx,FirstBlock}=4.32\) mW in this case. Therefore, we observe that low noise figure is more important when the number of active antennas is low (e.g., with AS and SVD with a few antennas), while low power consumption becomes crucial when the number of active RF chains at the receiver increases. Figure 5: Energy efficiency of the AS scheme as a function of the number of antennas (\(N_{\rm t}=N_{\rm r}\)), for \(d=\{50,400\}\) m.