Digital Backpropagation for Subcarrier-Multiplexing Systems With Nonlinearity Compensation Fusion

A novel simplified implementation structure is proposed for digital backpropagation in digital subcarrier-multiplexing systems (SCM-DBP) and one of its modifications, the SCM-DBP with infinite impulse response filters and reduced number of interfering subcarriers (IIR-RS-SCM-DBP). To the best of our knowledge, it is the first time to convert the serial calculation and compensation of self-subcarrier nonlinearity (SSN) and cross-subcarrier nonlinearity (CSN) to a parallel calculation and a fused compensation without affecting the nonlinear compensation (NLC) effectiveness. The performance is verified by a 9-channel wavelength-division multiplexing coherent numerical system with 120-GBaud 8-subcarrier dual-polarization 16QAM signal in each channel after 1600-km transmission. After verifying the robustness to multiple impairments, SCM-DBP adopting the fusion structure provides the same performance as before but saves about 4.5% NLC complexity. IIR-RS-SCM-DBP (4 interfering subcarriers) with the fusion structure provides about 10.8% NLC complexity reduction compared with the original IIR-RS-SCM-DBP, and about 63% NLC complexity reduction compared to SCM-DBP with about 0.16 dB penalty of
$Q^{2}$
factor. The proposed fusion structure helps realize a more cost-effective NLC in digital subcarrier-multiplexing systems.