# Accounting for Energy Cost When Designing Energy-Efficient Wireless Access Networks
## 1 Introduction
The developed framework is employed to provide an efficient use of the radio resources and a minimization of the energy consumption. Two methods are proposed, providing an optimal and near optimal solution to the problem. The work in [10] investigates the energy and the network performance of a wireless access network powered by the traditional electricity grid, a PV panel system and an energy storage system. An energy-aware management system is proposed. It consists of the management of the energy provisioning and storage system and the application of energy-reducing strategies, which aim to minimize the amount of energy bought from the traditional power grid. In these studies, and often in the literature, the aspect of the necessary energy cost to supply the base stations of the wireless access network is neglected. Nevertheless, studies that take care of minimizing the necessary energy cost are available in the literature. The work in [11] proposes a generic mixed-integer linear programming model to obtain job scheduling on a single machine to achieve the objective mentioned above, with the activation or deactivation of it according to the energy price. Energy prices are becoming more volatile, since they depend on real-time demand and generation. In fact, they are used in the DR (Demand and Response) scheme. This is a program of the DSM (Demand Side Management) of the electricity system, which consists of mechanisms that aim at modifying the consumer's demand profile, in time and/or shape, to make it match the supply to avoid overloads of the grid or the wasting of energy [12]. In this way, peaks higher than the normal demand are reduced. The presence of peaks in the power demand compromises the usage of renewable energy resources, since they are not reliable for the production of those amounts of energy. The DR acts against them with the introduction of the power utility's incentive (incentive-based approach) or with the variation of electricity price (price-based approach). In particular, during peak hours, customers are induced to avoid consuming energy because of higher energy prices or penalties. In this way, they are encouraged to shift their demand during off-peak hours because of lower energy prices or a discount on their bill. Concerning the price-based approach, different policies exist, as explained in [13]. For example, in the real-time pricing mechanism, prices vary over quite short periods (e.g., 1 h or 15 min), and they are released shortly in advance (the day before). In time-of-use pricing, they differ by time periods, but they remain constant within one period; in critical peak pricing, prices are increased in the case of critical overloads. In this paper, the attention is focused on the cost for the purchase of the energy needed for the supply of the base stations of an energy-efficient wireless access network. To the best of the authors' knowledge, this has never been investigated in this kind of network before. Our study builds on prior studies of the green-networking field, specifically the [14] one. The work in [14] introduces a capacity-based wireless access network, powered by a PV panel system, energy batteries and the power grid. It proposes an energy-management system. It consists of the management of the energy provisioning and storage system. Energy-saving strategies are also applied, which aim to reduce the amount of energy that should be bought from the power grid in case a renewable energy shortage occurs. In this study, strategies and algorithms, which aim at the minimization of the necessary energy cost in the described scenario, are designed and discussed. A strategy achieves the aforementioned goal towards the decrease of the power consumption. Others exploit the dynamism of the energy price. Finally, the reduction of the energy cost is obtained with the introduction of the network in the energy market.