Fronthaul-constrained cloud radio access networks: insights and challenges

TLDR

Cloud radio access networks promise lower CAPEX/OPEX and higher spectral and energy efficiency, yet their fronthaul links—critical for connecting baseband units to remote radio heads—often lack the capacity required to support these gains. This article surveys recent advances in fronthaul‑constrained C‑RANs, reviewing system architectures and key techniques. It examines how fronthaul constraints affect spectral/energy efficiency and user quality of service through compression, quantization, large‑scale coordinated processing, clustering, and resource‑allocation optimization, and identifies open issues in software‑defined networking, network‑function virtualization, and partial centralization.

Abstract

As a promising paradigm for fifth generation wireless communication systems, cloud radio access networks (C-RANs) have been shown to reduce both capital and operating expenditures, as well as to provide high spectral efficiency (SE) and energy efficiency (EE). The fronthaul in such networks, defined as the transmission link between the baseband unit and the remote radio head, requires a high capacity, but is often constrained. This article comprehensively surveys recent advances in fronthaul-constrained CRANs, including system architectures and key techniques. Particularly, major issues relating to the impact of the constrained fronthaul on SE/EE and quality of service for users, including compression and quantization, large-scale coordinated processing and clustering, and resource allocation optimization, are discussed together with corresponding potential solutions. Open issues in terms of software-defined networking, network function virtualization, and partial centralization are also identified.