Optimal Rate Allocation for Minimization of the Consumed Energy of Base Stations with Sleep Mode

In cellular networks, it is desirable to reduce the energy consumed by base stations as they contribute to a major percentage of the energy consumed by the network. In this paper, we consider the downlink scenario in a Macro cell in which the base station is required to satisfy its active users with a strict delay constraint. It is assumed that the consumed power of the base station is a linear function of its transmission power, and that the base station can switch to a sleep mode and operate at low power when no users are active. The base station is required to select the transmission rate to each user so as to minimizes the consumed energy. Two scheduling methods are considered to meet the users' demands: the first one is based on time division multiplexing and the other one is based on frequency division multiplexing. The rate allocation problem is formulated for both scheduling methods. For each scheduling method, the problem becomes a convex, non-linear optimization problem. We obtain the energy gains that are achieved by allowing the base station to switch to a sleep mode, and we show that time division scheduling is more energy-efficient than frequency division scheduling under usual operating constraints.