A Spectral-Efficient Coherent RoF Link for 5G Millimeter-Wave Transmission

A spectral-efficient radio over fiber (RoF) link transmitting two millimeter-wave vector signals at the same frequency is proposed and verified by simulations. At the transmitter, two millimeter-wave vector signals are respectively modulated on the intensity and phase of the optical carrier through a dual-parallel Mach-Zehnder modulator (DPMZM). By mixing with a three-line optical frequency comb, the two millimeter-wave signals are photonically down-converted and detected. After simple digital signal processing, the laser phase fluctuation between the two lasers is eliminated and the two signals are separated and demodulated respectively. In simulations, two 16-QAM microwave vector signals with a symbol rate of 100 Msym/s at 25 GHz are transmitted over 25 km single-mode fiber (SMF). The error vector magnitudes (EVMs) of the recovered signals are 8.28% and 7.6%. The channel isolation over 20 dB is obtained for each signal transmission.