Performance Comparison of DFT-Spread and Pre-Equalization for 8 × 244.2-Gb/s PDM-16QAM-OFDM

In this paper, we experimentally compared the performance of discrete-Fourier-transform spread (DFT-spread) and pre-equalization in a 244.2-Gb/s polarization-division-multiplexed 16-ary quadrature amplitude-modulation orthogonal frequency-division multiplexing (PDM-16QAM-OFDM) transmission system. The pre-equalization is effective to overcome the high-frequency power attenuation in the channel. However, the acquisition of static channel response for pre-equalization is really complicated and the peak-to-average power ratio (PAPR) of the signal after pre-equalization even becomes a little higher. The DFT-spread can be applied to simultaneously resist high-frequency power attenuation and reduce the PAPR of OFDM signal. The experimental results also show that one band DFT-spread demonstrates the best narrow optical filtering tolerance. The transmission distance for 8 × 244.2-Gb/s wavelength-division-multiplexing (WDM) PDM-16QAM-OFDM at the soft-decision forward-error correction threshold of 2.4×10^-2 is 2× 420 km based on pre-equalization, while extended to over 3×420 km based on one band DFT-spread, which well illustrates one band DFT-spread is more efficient for high-bandwidth coherent WDM-OFDM system.