On Resource Allocation for Downlink Power Minimization in OFDMA Small Cells in a Cloud-RAN

We consider the problem of minimizing the total downlink transmit power in an orthogonal frequency-division multiple access (OFDMA)-based cellular network composed of a single-antenna macrocell overlaid by multi-antenna small cells deployed in a cloud radio access network (C-RAN) architecture. More specifically, the C- RAN minimizes the total downlink transmit power subject to the quality of service (QoS) constraints for small cell user equipments (SUEs), power budgets of small cells, interference thresholds for macro UEs (MUEs), and practical fronthaul capacity constraints. This problem is a mixed integer nonlinear problem (MINLP). Moreover, the problem can become infeasible which necessitates the employment of some form of admission control (AC). Therefore, relying on the framework of successive convex approximation (SCA), we propose a low-complexity solution for the original non- convex MINLP by solving a series of convex problems, which is guaranteed to converge to a local optimum solution. Numerical results indicate the performance of the proposed formulation and demonstrate the underlying tradeoffs among the SUEs´ QoS requirements, number of admitted SUEs, total downlink transmit power, and the available fronthaul capacity.