Passive beamformer based remote beamforming scheme for radio-over-fiber systems: Experimental demonstration using 28-GHz band reflectarray

Abstract

This paper proposes and experimentally demonstrates a passive beamformer based remote beamforming scheme for millimeter-wave band radio-over-fiber systems. The proposed scheme can control the beam direction of remote radio units (RRUs) from the central station (CS); it yields extremely simple RRUs for flexible and cost-effective deployment. The proposed scheme sets a passive beamformer such as beamforming network, reflector, or lens in the RRU and different wavelengths are assigned to each input port of the passive beamformer. This configuration offers remote beam switching by just carrier wavelength switching at CS. Multi-beam operation can be also realized simply by using multiple wavelengths simultaneously. Experiments on a 28 GHz band reflectarray are conducted. The feasibility of remote beam switching by wavelength switching is confirmed. 5G signal transmission over 20 km of single-mode fiber and 6.3 m air link is successfully achieved with error vector magnitude values of 2.71–3.55%, which satisfies the 3GPP requirements of 8%.