Joint Cell Selection and Activation for Green Communications in Ultra-Dense Heterogeneous Networks

In this paper, we jointly perform the cell selection and activation (CSA) to maximize the network energy efficiency (EE) under users' long-term rate constraints for green communications in ultra-dense heterogeneous networks (UD-HetNets). The finally formulated problem is in a mixed-integer fractional form and hard to tackle. We first transform it into a parametric subtractive form, by which we reach its solution through a three-layer iterative algorithm. The first layer searches the EE parameter using a bisection method; the second layer alternately optimizes the CSA indices; the third layer solves the CSA problems using a dual decomposition method and a fixed point iteration respectively. At last, we give some complexity and convergence analyses for the designed algorithm, and investigate the impacts of different network parameters on system performance. The simulation results show that the cell activation (CA) introduced in the cell selection (CS) is good option to reduce the energy consumption and mitigate interference.