Real-time all-digital radio-over-fiber LTE transmission

Radio-over-fiber is a key-enabling-technology for next generation wireless networks. To support an increasing number of antennas, a CloudRAN approach that maximally aggregates base station functionality of the different antenna sites is the most economically feasible. To support light weight antenna units, analog radio-over-fiber is most promising. To mitigate linearity constraints of optical modulators, an all-digital transmitter can be used. In this paper, LTE transmission is demonstrated over 200 m OM4 multimode fiber using a VCSEL and a resonant transimpedance amplifier. The VCSEL is directly modulated with a high-speed 2-level signal generated in real-time on an FPGA. After reception of this signal, the adjacent channel power ratio was measured to be −45.6 dB. This is within the LTE specifications, proving this is a cost and power effective solution for next generation wireless networks.