Robust Energy-Efficient Downlink Resource Allocation in Heterogeneous Networks with Outage Probability Constraint

With the development of the fifth generation communication technology, improving energy efficiency (EE is defined as the ratio of the system throughput over the total power consumption) of wireless communication becomes a hot topic, which has attracted wide attention from industry and academia. Heterogeneous networks (HetNets) have been considered as a new promising technique for expanding network coverage and improving EE. Robust resource allocation is a huge challenge when uncertainty parameters are involved in this issue. The problem is more significant in HetNets since perfect channel state information is not available at femtocell base station's transmitters. In this paper, we study the downlink resource allocation in HetNets under outage probability constraint, and formulate the EE maximization problem as a nonlinear fractional programming problem. In order to solve the fractional programming problem, firstly, we transform the original problem into an equivalent optimization problem in a parametric subtractive form. Then based on the exponential distribution model under Rayleigh fading environment, the probability constraint is transformed into a deterministic constraint. Finally, we propose a two-loop iteration algorithm to find the optimal solution by using Dinkelbachs method and Lagrangian dual decomposition method. Simulation results demonstrate the convergence and the effectiveness of the proposed algorithm.