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 basestation 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. (Nokia contributions relate to the RF signal generation at 3.44 GHz carrier frequency implemented in an FPGA and to joint experiments leading to the results in Figure 7 and 8.)