Fig. 4. (a) Comparison of the impact of transmission distance (km) on performance (in BER) using LDC and different DBP techniques; (b) Performance improvement of 112 Gbit/s DP-16QAM transmission with LDC and 10 steps/span BLSS DBP over 2400 km
Firstly, the impact of increasing the transmission distance for different signal processing techniques on overall system performance is examined. The DSP-based LDC, constant step size (CSS DBP), conventional LSS DBP, and the proposed BLSS DBP algorithms for the single-channel transmission are considered. The time-domain FIR filter implements the LDC. The number of spans controlled by a loop counter is increased serially to vary the transmission distance. Fig. 4(a) shows the BER against the transmission distance. It is observed that generally, the DBP algorithms extend the transmission distance by several kilometers as they cancel the distortions associated which long-haul communication. Specifically, at the ~10-3hard-decision forward error correction (HD-FEC) threshold, the distance is extended from 2560 km to 3040 km, 3200 km, and 3520 km by implementing the CSS, LSS, and BLSS DBP algorithms, respectively. As expected, the logarithmic step size distribution shows better performance when compared to the constant step size distribution. Also, the proposed BLSS DBP algorithm is more effective for compensating intra-channel nonlinear self-phase modulation. For a 2400 km transmission, the BLSS DBP algorithm achieves a Q-factor improvement (∆Q) of 2.36 dB at 13 dBm signal launch power, as shown in Fig. 4(b). The inset shows the respective constellation diagrams.