Analog optical X-haul in cell-free network architecture for 6G

Functional splitting in next-generation mobile networks enables new opportunities for millimeter wave radio over fiber systems. Since a cell-free network architecture is a possible way to enable uniform high data rates, we propose a scalable optical full-duplex crosshaul with simplified radio units, where a low-cost directly modulated laser transmits a 1.5 GHz intermediate frequency uplink signal. The scheme is experimentally validated over a seamless antenna channel, showing efficient operation at 40 GHz. System performance is verified for bandwidths up to 400 MHz using 5 G modulation formats, with the error vector magnitude remaining well below standard limits.