Linearization for Microwave Photonic SEFDM Transmission Systems Based on Random Displacement of Constellation Points

A linearization method for microwave photonic (MWP) spectrally efficient frequency-division multiplexing (SEFDM) transmission systems is proposed to compensate for the inherent inter-carrier interference (ICI) of the SEFDM signal and reduce the third-order intermodulation distortion (IMD3) introduced by the MWP transmission link. The received SEFDM signal experiences several iterations, and in each iteration, the SEFDM signal is decoded into a bit sequence, which is remapped to quadrature-amplitude modulation (QAM) symbols to reconstruct the interference signals for canceling the distortion. By introducing the random displacement into the regenerated QAM symbols, it is experimentally verified that the cooperation of the random displacement and the forward error correction (FEC) can significantly improve the modification ability of the iterative structure, which enables the method to maintain good performance despite high interference and low signal-to-noise ratio. For an SEFDM signal with a bandwidth compression factor of 0.8 and a large peak-to-peak voltage of 550 mV before amplification, the correct bit information can be recovered by the proposed method with the error vector magnitude (EVM) optimized from 30.2% to 2.6%. In comparison, the EVMs remain at relatively high levels of 15.4% and 4.3% in the absence of the random displacement or the FEC mechanism, respectively.