# Design of an Energy Efficient Future Base Station with Large-Scale Antenna System
## 4 Numerical Results  
In this section, we show the numerical results for the proposed BS. The reference structure used for the performance analysis is presented in Figure 7. As shown in the figure, one BS case is considered for simplicity. Several algorithms can be incorporated into the modern for BB processing. In this paper, we assume all other processing in the modem is the same, except for the precoding scheme. For the high data rate, we can use ZF precoding with a high complexity. To reduce the complexity, we can use MF precoding with sacrificing of the data rate. This means that there are two kinds of modem algorithms in the reference model. It is also quite obvious that we can include more algorithms in the modem to improve the EE performance. For RF processing, a better DAC and oscillator consume more power. Several RF groups, which include a different level of DAC/oscillator/filter, are incorporated into the BS, and we can choose an appropriate RF block depending on the situation, as shown in Figure 7. For PA processing, we adjust the bias of the PA and adjust the TX power/actual power consumption of the PA.  
First, we show a performance analysis for the case with a PA power consumption adjustment. Based on the power model shown in Section 2.1 and the reference model in Figure 7, we can compare the case of the reference radiation power, 40 W, which is usual for the current BS when BW = 10 MHz and that of a reduced radiation power of 4 W, which is 10% of the radiation power of the current BS. We assume a 25% PA efficiency, as mentioned in Section 2.1. Then, the reference PA power consumption is 160 W, and the reduced PA power consumption is 16 W.  
In Figure 8, we present the total power consumption and the power consumption of each component when the VLSI processing efficiency \(\varrho\) = 5 Gflop/W (Figure 8a,b), and 50 Gflop/W (Figure 8c,d), \(P_{RF}=1\) W, \(P_{PA}=40\) W and 4 W, \(K=0.1\)\(N_{t}\). The number of TX antennas ranges up to  
Figure 7: Reference BS structure used in the performance analysis. \(N_{t}=600\). As shown in the figure, \(P_{total}\) increases linearly as the number of TX antennas increases. Here, the power reduction indicates a reduction in the PA power consumption by a factor of 10, i.e., from 160 W to 16 W. Choosing different algorithms for BB processing is not very helpful in reducing the \(P_{total}\), as shown in Figure 8. One more interesting thing is that the BB processing power consumption can take more power consumption than the PA power consumption, which is a very unusual case for current BS systems. From Figure 8a,b, the threshold point for this situation is when \(N_{t}\) is more than 247 for ZF and 262 for MF. When the number of TX antennas is more than 247/262, the BB processing power consumption takes a greater portion than the reduced PA power consumption. When the BS has large amounts of TX antennas, the RF power consumption can take a greater portion than the PA power consumption in \(P_{total}\), as is well known. Even in the case of \(P_{tx}=40\) W, if the number of TX antennas is more than 160, the RF power consumption takes a greater portion than the PA power consumption in \(P_{total}\). The situation between the BB power consumption and the reduced PA power consumption can be different if the VLSI processing efficiency, \(\varrho\), is higher than that of the previous case. In the case of \(\varrho=50\) Gflop/W, the BB processing power consumption is lower than the PA power consumption, even for \(N_{t}=600\), as shown in the right of Figure 8. All other characteristics in the case of \(\varrho=50\) Gflop/W are very much similar to those when \(\varrho=5\) Gflop/W. Now, let us look at the TP and EE based on the proposed BS structure. From now on, we use the case of \(\varrho=50\) Gflop/W. Figure 9 shows TP/EE versus the number of TX antennas. For the numerical simulations, we use a macro-cell type setup with a 2-GHz carrier frequency. The path loss in dB is modeled as \(128.1+37.6\) log(d) with distance \(d\) in kilometers [4; 33].