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.