C-RAN at Millimeter Wave and Above: Full-Beamspace Radio Access Architecture

We report progress toward a RF-photonic centralized radio access network (C-RAN) architecture for distributed multi-point transmission over millimeter wave (mmW) spectra. The architecture comprises three components: (1) access points (APs) employing RF-photonic phased arrays capable of multibeam and multiband operation; (2) an RF-photonic beamspace processor unit (BPU) that carries out centralized beamspace processing across multiple APs, and (3) a single-fiber fronthaul capable of full-dimensional beamspace transportation between the BPU and the APs. It is shown that the photonic portion of the AP and the BPU can be extended with minimal alteration to include arrayed waveguide grating (AWG) functionality. The AWG feature allows a direct conversion between RF beams and optical wavelengths at the AP and the BPU, providing a scalable means of transporting the entire beamspace over a fronthaul network employing single-fiber wavelength division multiplexing (WDM).