Investigation and comparison of digital backward propagation schemes for OFDM and single-carrier fiber-optic transmission systems

The performance of orthogonal frequency-division multiplexing (OFDM) and single-carrier (SC) fiber-optic transmission systems with digital backward propagation (DBP) are compared. Sixteen quadrature amplitude modulation (QAM) is used for both systems with the bit rate of 100Gb/s. The results show that OFDM and SC with Nyquist pulses (SC-Nyquist) have a superior performance as compared to SC with raised-cosine pulses (SC-NRZ) when the DBP is used. We also studied the impact of electrical filter bandwidth and nonlinear phase/amplitude noise on the performance. As the filter bandwidth increases, the performance improves for the case of ideal BP for both OFDM and SC systems when the signal-to-noise ratio (SNR) is large. The analysis of nonlinear phase/amplitude noise revealed that it causes significant impairments for SC-NRZ systems and less impact on OFDM and SC-Nyquist systems, which explains the performance advantage of OFDM/SC-Nyquist over SC-NRZ when the DBP is used.