# Design of an Energy Efficient Future Base Station with Large-Scale Antenna System
## 1 Introduction  
Communication technologies that can increase channel capacity, as well as energy efficiency (EE) would be a key factor for future wireless systems. An increase in EE is very important because the continuous increase in data demanded by end-users results in a high cost both from an environmental and technological perspective. It is well known that base stations (BS) consume around 60%-80% of power consumption in cellular networks [1; 2; 3]. Thus, reducing the power consumption of a BS is quite important to reduce the operational costs, as well as the carbon footprint. For this reason, researchers have actively investigated this problem [1; 2; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15]. Most work has concentrated on implementing the BS on/off technique, which means that the BS is turned off when there is no nearby traffic [1; 2; 9; 10; 12; 14], as well as on conducting theoretical high-level analyses and optimizations to reduce the BS power consumption [7; 8; 11; 13]. However, the BS on/off technique is only beneficial for an empty network, which rarely happens in actual networks. Furthermore, there could be many real implementation obstacles for theoretical, high-level optimization techniques.  
In this paper, rather than presenting a BS on/off mechanism or solving the theoretical optimization problem, we focus on more practical implementation aspects to improve the EE of cellular systems. We propose a future energy-efficient BS structure and its related operation using a realistic power model for real implementation. Due to the limited spectrum resources, it is also inevitable for the number of transmitter (TX) antennas in the BS to continuously increase [11]. Thus, we assume that a future BS has a large number of TX antennas, that is a large-scale (LS) antenna system or LS multiple-input multiple-output (MIMO) [16; 17; 18]. Actually, in the case of a BS with LS-MIMO, the resource allocation problems are easier to solve if the channel properties provided by LS-MIMO systems are exploited smartly [19; 20].  
The proposed energy-efficient BS consists of five main components: a central management apparatus, power controller, EE calculator, radio site-dependent parameter space (RSD-PS) and determiner. The central management apparatus manages the appropriate power consumption of each BS located in a pre-defined range. The power controller controls the power control of each related device. The EE calculator, which operates based on the power consumption and data rate estimator, provides the power control metric. The RSD-PS accumulates information and supports the increase in EE according to past operation information. The determiner for each decision unit decides the operation points of the power-related devices for a pre-defined time duration. Each component can also be divided into several sub-components. With these components, we show how to systematically increase the EE of the proposed future BS. The BS could also be used as a hub for a LS sensor system for a smart city or such.  
In what follows, we introduce the system model in Section 2. In Section 3, we present the proposed BS structure and the method used to systematically increase the EE of the BS. In Section 4, we present numerical results based on a reference future BS model, showing the effectiveness of the proposed structure and method. Finally, the conclusions are drawn in Section 5.