Linearization for microwave photonic SEFDM transmission systems based on an iterative algorithm

Spectrally efficient frequency-division multiplexing (SEFDM) is a promising solution to increase communication spectral efficiency, which can pack even more sub-carriers than the orthogonal frequency-division multiplexing in a given bandwidth. However, the cost is the introduction of inter-carrier interference (ICI), increasing the difficulty of signal reception and demodulation. When SEFDM signals are incorporated into a microwave photonic link, in addition to ICI, the nonlinear interference introduced by the nonlinearity of the microwave photonic link should also be considered. In this work, an iterative algorithm for microwave photonic SEFDM transmission systems is proposed to compensate for the inherent ICI of the SEFDM signal and reduce the third-order intermodulation distortion (IMD3) introduced by the microwave photonic transmission link. In the digital algorithm, the received 16 quadrature-Amplitude modulation (QAM) SEFDM signal experiences several iterations, and in each iteration, the input SEFDM signal is modified, demodulated, and forward error correction (FEC) decoded into a bit sequence, which is remapped to QAM symbols to reconstruct the interference signals for canceling the distortion. Experimental results show that 16-QAM SEFDM signals with a bandwidth compression factor of 0.85 and high nonlinearity are successfully recovered from a microwave photonic link. The proposed method integrates the demodulation of SEFDM signals with the elimination of IMD3. Due to the employment of the FEC, compared with the traditional iterative ICI compensation (IIC) algorithm only for SEFDM signal demodulation, the signal demodulation capability is improved, and the improvement of signal demodulation capability also provides great help for the elimination of IMD3.