Centralized Energy-Efficient Multiuser Multiantenna Relaying in Next-Generation Radio Access Networks

Abstract

This paper addresses the design of a multiuser relaying subnetwork within a cloud radio access network (C-RAN) from an energy-efficient perspective. In the relaying subnetwork, multiple source–destination pairs communicate with the assistance of multiple remote radio heads (RRHs) connected to the baseband unit pool. Exploiting the flexible centralized processing structure of C-RAN, where RRHs can be adaptively activated/deactivated, we formulate the problem as a quality-of-service (QoS) based network energy minimization problem via joint RRH selection and relaying matrix optimization. Since the resultant optimization problem is nonconvex and mathematically challenging, we propose an iterative solution based on the concept of the re-weighted $l_1$ norm, along with a block-coordinate descent type algorithm. The active RRHs are then determined in a single attempt by thresholding a group sparsity pattern associated with the set of all RRH relaying matrices. To circumvent a potentially undesirable condition, where the selected subset of RRHs fails to simultaneously satisfy all the destination users’ QoS levels, we conceive a UE admission control mechanism for overcoming the associated infeasibility problem. Our simulation results demonstrate the explicit benefits of the proposed design approach, which results in a significantly lower energy consumption of the relaying subnetwork than conventional cooperative relaying.