Abstract
Energy efficiency is becoming an important feature for designing the next generation of communication networks, as are the multiplication of access points and the reduction of their coverage area. In this article we survey the latest development in energy-efficient scheduling, a.k.a. green scheduling, for both classic and heterogeneous cellular networks. We first introduce the main system model and framework that are considered in most of the existing green scheduling works. We then describe the main contributions on green scheduling as well as summarize their key findings. For instance, green scheduling schemes have demonstrated that they can significantly reduce transmit power and improve the energy efficiency of cellular systems. We also provide a performance analysis of some of the existing schemes in order to highlight some of the challenges that need to be addressed to make green scheduling more effective in heterogeneous networks. Indeed, the coordination between tiers and the rate fairness between the users of different tiers are important issues that have not yet been addressed. In addition, most existing designs exhibit a computational complexity that is too high for being deployed in a real system.