A Novel Polarization Multiplexing RoF-FSO System with 128QAM-OFDM Downlink Signal

An improved polarization multiplexing radio over fiber free space optics (RoF-FSO) system using 128-ary quadrature amplitude modulation (128QAM)-orthogonal frequency division multiplexing (OFDM) modulation is proposed. The model analysis of the RoF-FSO system is carried out. The optical spectra, electrical frequency diagrams, constellation diagrams and received power versus bit error rate (BER) and error vector magnitude (EVM) of 128QAM-OFDM signal before and after transmission are tested by numerical simulation. 70Gbit/s 128QAM-OFDM signal realized transmission and receiving in 1km free space, and the BER is 10
^-3
when received optical power is -2.5dBm after transmission. The scheme improved the transmission efficiency of the FSO system, resisting fiber dispersion, resisting channel fading, and reducing signal bandwidth.