Linearization for Microwave Photonic OFDM Transmission Systems Using an Iterative Algorithm Based on FEC Mechanism

A digital linearization algorithm is proposed to reduce the third-order intermodulation distortion (IMD3) for the microwave photonic (MWP) orthogonal frequency-division multiplexing (OFDM) transmission system with intensity modulation and direct detection. Forward error correction (FEC) is added to the OFDM signal to suppress the IMD3 in conjunction with an iterative operation. The distorted OFDM signal from the MWP system goes through iterative operations including fast Fourier transform, demodulation, error correction, signal reconstruction, and interference cancellation until the output converges. Compared with the non-iterative method and the iterative method without FEC mechanism, the proposed method has a significant advantage in linearizing signals with large nonlinearity and low signal-to-noise ratio. 200-Msym/s 64 quadrature-amplitude modulation (64-QAM) OFDM signals with a large peak-to-peak voltage of 650 mV are amplified by a power amplifier and then input to the MWP link and linearized by the FEC-based iterative method. The results show that the error vector magnitudes (EVMs) of the OFDM signals can be optimized from 13.1% to 2.9% and from 13.4% to 6.3% when the output
E_b/N₀
from the MWP link is about 35 dB and 13.5 dB, respectively. Besides, a 3-GHz 64-QAM OFDM signal is successfully transmitted through a 25-km standard single-mode fiber with an EVM of 3.9% after linearization.