Large-scale antenna operation in heterogeneous cloud radio access networks: a partial centralization approach

To satisfy the ever increasing capacity demand and quality of service requirements of users, 5G cellular systems will take the form of HetNets that consist of macrocells and small cells. To build and operate such systems, mobile operators have given significant attention to cloud radio access networks, C-RANs, due to their beneficial features of performance optimization and cost effectiveness. Along with the architectural enhancement of C-RAN, largescale antennas (a.k.a. massive MIMO) at cell sites contribute greatly to increased network capacity either with higher spectral efficiency or through permitting many users at once. In this article, we discuss the challenging issues of CRAN- based HetNets (H-CRAN), especially with respect to large-scale antenna operation. We provide an overview of existing C-RAN architectures in terms of large-scale antenna operation and promote a partially centralized approach. This approach remarkably reduces fronthaul overheads in C-RANs with large-scale antennas. We also provide some insights into its potential and applicability in the fronthaul bandwidth-limited H-CRAN with large-scale antennas.