A Joint Algorithm for Base Station Operation and User Association in Heterogeneous Networks

In this paper, we present an algorithm that performs base station (BS) switching-on/off and user terminal (UT) association jointly in heterogeneous networks composed of cellular networks and wireless local area networks (WLANs). We first formulate a general problem which minimizes a total cost function, which is designed to balance the energy consumption of overall network and the revenue of cellular networks. Given that the time scale for determining the set of active BSs is much larger than that for UT association, we decompose the problem into a UT association algorithm and a BS switching-on/off algorithm, and then obtain an optimal UT association policy for the UT association problem. Since BS switching-on/off problem is a challenging combinatorial problem, we propose two heuristic algorithms based on the total cost function and the density of access points of WLANs within the coverage of each BS, respectively. Numerical results demonstrate that the proposed algorithms can considerably reduce energy consumption compared with the case where all the BSs are always turned on.