Performance Evaluation of Multi-Gb/s Sub-6 GHz Signals over Bidirectional Microwave Photonic Links for Urban and Rural Areas

We propose and experimentally demonstrate a full-duplex fiber-space-fiber system in the 5G sub-6 GHz frequency bands for simultaneous transmission of multi-Gb/s downlink and uplink signals. In the downlink direction, transmission of a 2.4-Gb/s 64-quadrature amplitude modulation (64-QAM) signal at 5-GHz over a seamless optical link of 10-km standard single-mode fiber (SSMF), 1.2-m free-space optics (FSO) and 1.4-km SSMF with error-vector magnitude (EVM) lower than 4% is achieved by using external modulation. In the uplink direction, a directly modulated laser is employed to transmit 2-Gb/s 4-QAM signal at 3.5-GHz over the same hybrid channel with the measured EVM below 11% and thus value satisfying the 3GPP limit. The proposed system provides a practical solution for extension or recovery of broadband wireless connectivity.