# Design of an Energy Efficient Future Base Station with Large-Scale Antenna System
## 3 Energy-Efficient BS Structure and Related Operation  
To achieve a high EE for the BS, it is essential to control some of the important TX parameters there. We can divide the main BS power consumption components in PA, RF (except PA) and BB and make out each component to be a power-adjusting component. The PA is the most power-hungry device in the current BS, but this could change depending on the situation of a future BS. Since a future BS could have a large amount of RF chains connected to each antenna, it is also possible for the RF chain to consume more power than the PA. In contrast to the PA, which can reduce the power consumption by using a beamforming effect, there are no distinct sources to reduce the RF chain power consumption. The BB may consume less power when compared to the PA and RF. However, it is better to include it as one of the adjustable parameters to enhance the EE. The three main components can be controlled as shown in Figure 4.  
An energy-efficient future BS is quite obviously a feedback system. It mainly receives information of the power consumption from the BS TX unit and information regarding the data rate from the user terminals. As shown in the figure, the power control unit controls each component based on the measured EE parameters. The proposed BS measures the data rate, and if it is not in a satisfactory range, it provides an input to power the adjustable unit to increase the power consumption of some of the components. Then, based on the power adjustment of each component, the data rate estimation unit measures the data rate again and checks if it is in the satisfactory range, and so on. If the power consumption is too high over a pre-defined threshold, then the data rate could also be reduced to obtain satisfactory EE performance. Based on the high-level concept of a future BS, the detailed block diagram of the proposed BS structure is described in Figure 5.  
Figure 4: The high level conceptual figure of the energy-efficient future base station (BS). Figure 5: Block diagram of the proposed BS structure. First, let us observe two units, the power consumption estimation unit and the data rate estimation unit, which are tightly connected with the fundamental TX/RXunit of the BS. The BS provides information for the units based on feedback from self-measurement and user terminals, then EE (bps/W) can be derived based on the results. All information (power consumption, data rate, EE) is given to the decision unit, which can then decide each component's power consumption, i.e., PA, RF and BB. The decision unit provides feedback on the decision to the fundamental TX/RX unit of the BS. Then, the BS performs power control based on the feedback information. There are three more components in this structure, as shown in the figure. The first one is the central BS management unit. This apparatus can be used for multi-BS power control/optimization. The central BS management unit monitors all nearby BSs and adaptively allocates the allowable maximum power for each BS. Then, each BS only allocates power for each component based on the total allowable power consumption criterion. The second one is the user terminal. In particular, the data rate can be easily measured with a user terminal. Furthermore, it is beneficial for the user terminal to give feedback regarding the current channel condition. The last one is the RSD-SP. The RSD-SP is the apparatus that accumulates the history of optimum BS operation, and supports the decision unit to determine the operating points of BS based on the accumulated history whenever necessary. For example, RSD-PS monitors the BS operation, such as the level of radiation power, the level of the resolution of the RF chain, the level of BB processing based on operating parameters, such as the number of TX antennas, the number of users, system bandwidth, the channel condition, and so on. After having accumulated enough, the RSD-PS can assist to maintain the high EE BS by providing the history of optimum EE operation points based on operation parameters.