Load dependent optimal ON-OFF policies in cellular heterogeneous networks

The use of small cells has been proposed to increase system capacity by installation of base stations close to user location. Proximity of the base station with the user equipment also implies lesser power requirement for transmitting the same information. Thus one may expect improvement in energy efficiency. But installing a large number of base stations can also lead to an increase in the total energy consumption of the system. To combat this, mechanisms have been proposed to switch OFF these base stations at times of low load. In this paper, we consider the problem of finding the fraction of base stations that can be switched OFF while maintaining quality of service (measured in terms of the average waiting time of users), for given load conditions. We also obtain the optimal switch OFF pattern. We do this in two steps. First, we determine the optimal ON-OFF pattern of base stations and user-base station association policy for a fixed fraction of base stations to be switched OFF. Then, we find the maximum fraction of base stations that can be switched OFF for given load conditions.