Third-order sparse Volterra equalizer based nonlinear suppression method for WDM PDM CO-GFDM systems

Abstract

Compared to orthogonal frequency division multiplexing (OFDM), generalized frequency division multiplexing (GFDM) has advantages such as low peak-to-average power ratio (PAPR) and high spectral efficiency (SE). These features enable GFDM to be applied in long-haul coherent optical (CO) fiber transmission systems and to be combined with techniques such as polarization-division multiplexing (PDM) and wavelength-division multiplexing (WDM) to achieve Terabit-level transmission rate. However, the nonlinear effects introduced by long-haul optical fiber transmission evidently degrade the performance of WDM PDM CO-GFDM system. To the best of our knowledge, no existing researches have focused on nonlinear suppression for WDM PDM CO-GFDM system. Meanwhile, it is known that the sparse Volterra model based compensator can achieve similar bit error rate (BER) performance compared with traditional full Volterra compensator while maintaining lower complexity in nonlinear effect compensation. In this paper, we proposed 3rd-order sparse Volterra equalizer (SVE) for WDM PDM CO-GFDM system. We systematically introduced the principle of WDM PDM CO-GFDM system and deducted its nonlinear channel model based on 3rd-order Volterra series. Then we theoretically deduced the principle of sparse Volterra model, the structure of train sequence and the operation of estimating the coefficients of Volterra kernels using recursive least squares (RLS) algorithm. Simulation results demonstrate that, WDM PDM CO-GFDM system possess significantly lower BER compared with WDM PDM CO-OFDM system while achieve evidently higher net bit rate and net SE. Furthermore, for a 16-QAM modulated WDM PDM CO-GFDM simulation system with high data rate (eg. 1.6 Tbit/s sampling rate, 1.39 Tbit/s net bit rate and 138.74 bit/s/Hz net SE), the 3rd-order Volterra model based method improves the maximum transmission distance by approximately 33% compared to the 1st-order Volterra model for WDM PDM CO-GFDM system. Besides, while achieving similar BER performance, the computational complexity of the SVE is significantly decreased compared to the traditional Volterra compensator.