Resource Allocation and Power Control in Cooperative Small Cell Networks With Backhaul Constraint

A joint resource allocation (RA), user association (UA), and power control (PC) problem is addressed for proportional fairness (PF) maximization in cooperative multiuser downlink small cell networks with limited backhaul capacity, based on orthogonal frequency division multiplexing. Previous studies have relaxed the per-resource-block (RB) UA and RA problem to a continuous optimization problem based on long-term signal-to-noise ratio, because the original problem is known as a combinatorial NP-hard problem. We tackle the original per-RB UA and RA problem to obtain a near-optimal solution with feasible complexity. Motivated by the fact that the condition for obtaining the near-global solution with the dual problem approach is rarely satisfied for increasing number of users, we derive explicit first order optimality conditions to obtain a 2-distance ring solution of the primal UA and RA problem, and propose a sequential optimization method. In addition, we propose a PC algorithm based on the first order KKT optimality conditions, in which transmission power of each RB is iteratively updated. The overall proposed scheme can be implemented with feasible complexity even with a large variable dimension. Numerical results show that the proposed scheme achieves the PF close to its outer-bound. Though there have been extensive studies on UA, RA, and PC in multicell networks, the proposed scheme is first to closely achieve the optimal PF performance in frequency-selective fading channels with feasible computational complexity.