38-GHz millimeter wave beam steered fiber wireless systems for 5G indoor coverage: architectures, devices, and links

Millimeter wave (mm-wave) beam steering is a key technique for the next generation (5G) wireless communication. The 28 and 38-GHz bands are widely considered as the candidates for 5G. In the context of indoor coverage, fiber-wireless systems with multiple simplified remote antenna sites are attractive to avoid the indoor coverage problem caused by the high wall penetration loss of mm-wave signals. To allow enough antenna gain at the mm-wave bands, radio beam steering (and beamforming) is desired. Combining fiber-wireless system with remotely controlled photonic mm-wave beam steering can bring significant advances in terms of energy efficiency and cost. In this paper, we explore two kinds of indoor fiber-wireless network architectures for such mm-wave beam steering. Then, we discuss and investigate the key enabling device, which is an arrayed waveguide grating feedback loop (AWG-loop). Based on the AWG-loop, we further design two fiber-wireless links to accommodate the two network architectures. Both links with bit rates from 50 Mb/s to 8 Gb/s per spatial channel are experimentally demonstrated with a 38-GHz carrier frequency. The advanced reversely modulated optical transmitter and half-cycled 16 quadrature amplitude modulation (QAM-16) are employed to realize a simplified mm-wave beam steered fiber-wireless link with the record-breaking 16-b/s/Hz (4 spatial channels × 4/s/Hz) spatial-spectral efficiency in its kind.