Hybrid Photonic Beamforming for 5G Downlink Millimeter Wave MIMO Communication

Millimeter wave communication is going to play important roles for the coming 5G wireless era since it has large bandwidth from 24GHz to 300GHz. Massive MIMO antenna arrays provide high gain and are used to combat high loss of mmwave signals. Conventional fully digital beamforming architecture for massive MIMO antenna arrays increases complexity and hardware cost as it requires a large number of RF chains for each antenna elements. An alternative solution is to design a hybrid beamformer where analog and digital beamformers reduce complexity and hardware constraints. Other important requirements for 5G network are low power consumption, high bandwidth and high spectral efficiency. The use of photonic solutions can dramatically improve power efficiency, and bandwidth utilization. Besides, photonic based true time delay lines (TTDs) avoid beam squint or beam pointing error over large bandwidth. In this paper, we demonstrate hybrid photonic beamformer for downlink remote radio access. We replaced RF phase shifters by ring resonator based analog beam-forming. Analog beamformer is located in remote access and the digital beamformer is implemented in baseband unit which is located in central office. The central office and remote radio access are connected by fronthaul multicore fibers which are used for spatial multiplexing to increase spectral efficiency. Orthogonal matching pursuit (OMP) based Hybrid beamforming algorithm implemented in baseband unit controls and optimizes the required group delay distributions and 3D beamforming.