# Accounting for Energy Cost When Designing Energy-Efficient Wireless Access Networks
## 2 Materials and Methods  
An LTE-A (Long-Term Evolution-Advanced) capacity-based wireless access network is considered. Capacity-based means that the network responds to the instantaneous bit-rate demand of active users in the considered area. The link budget parameters are summarized in Table 1. The considered area is 0.3 km\({}^{2}\) of the suburban environment of the city center of Ghent, in Belgium (orange rectangle in Figure 1). It is composed of a group of macrocell base stations and/or microcell base stations. It is powered with solar panels and equipped with batteries. The energy production of the PV panels is predicted with the data from [15]. The adopted trace reports data, provided on an hourly basis, about the power output obtained per each kWp of nominal capacity of the PV panel system. The values of renewable energy production are derived based on real data of solar irradiation in the considered area. They are observed in the week from 3 January-9 January during the typical meteorological year. In this way, the worst case scenario in terms of power generation is considered. These data are related to the city of Turin, since those of Ghent are not available. Energy losses due to the efficiency of PV modules and to the normal PV system operation are taken into account. For energy harvesting, lead-acid batteries represent a common technology adopted in renewable energy systems. A set of lead-acid battery units, each with a capacity of 200 Ah and a voltage 12 V, is hence assumed as storage in this work. Storage losses are neglected, occurring both during the battery charge and discharge and for the energy transfer and transmission. The energy generated by the panels is fed into the batteries, from which the base stations drain the energy. In case the batteries are discharged, the base stations are supplied by the traditional power grid. The renewable energy generator system of 100 kWp and the energy storage of 50 kWh are shared among all the base stations. The energy management decisions are made in a centralized way for all the base stations. In this way, decisions are based on the total available energy and the total power demand. The real-time pricing is considered for the energy prices, which are provided by the Belgian power operator [16]. They vary every hour, as shown in Figure 2.  
Figure 1: The considered suburban area of 0.3 km\({}^{2}\) (orange box) of the city center of Ghent, in Belgium, with macrocell base stations (blue points) and microcell base stations (orange points). Three different strategies are proposed, and different configurations are considered. Their performances are evaluated in terms of:  
* gross outgo: this is the amount of money spent to buy energy from the power grid: \[total\ outgo=\sum_{k=1}^{N}energyBought[k]\cdot energyPrice[k]\] (1) \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Macrocell Base Station** & **Microcell Base Station** \\ \hline Frequency & & 2.6 GHz \\ \hline Maximum input power antenna & 43 dBm & 33 dBm \\ \hline Antenna gain base station & 18 dBi & 4 dBi \\ \hline Antenna gain mobile station & 2 dBi & \\ \hline Soft hand over gain & 0 dB & \\ \hline Feeder loss base station & 0 dB & \\ \hline Feeder loss mobile station & 0 dB & \\ \hline Fade margin & 10 dB & \\ \hline Yearly availability & 99.995\% & \\ \hline Cell interference margin & 2 dB & \\ \hline Bandwidth & 5 MHz & \\ \hline \multirow{6}{*}{Receiver SNR} & 1/3 QPSK = -1.5 dB, \(1/2\) QPSK = 3 dB, \(2/3\) QPSK = 10.5 dB, \(2/3\) QPSK = 10.5 dB, \(4/5\) IQ-QAM = 23 dB, \(2/3\) 64-QAM = 29.4 dB \\ \hline Used subcarriers & 301 \\ \hline Total subcarriers & 512 \\ \hline Noise figure mobile station & 8 dB \\ \hline Implementation loss mobile station & 0 dB \\ \hline Height mobile station & 1.5 m \\ \hline Coverage requirements & 90\% \\ \hline Shadowing margin & 13.2 dB \\ \hline Building penetration loss & 8.1 dB \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Link budget parameters for the LTE-A macrocell and microcell base station.