Fig. 5. (a) Comparison of the performance (Q) of transmissions at different symbol rates implementing the BLSS DBP technique; (b) Performance benefits (Q) of LDC, CSS DBP, LSS DBP, and BLSS at NLT for 12.5 GBaud, 14 GBaud, 21 GBaud, and 28 GBaud over 2400 km
As demonstrated by Fig. 5, the performance benefit of the logarithmic step size distribution is dependent on the signal bandwidth, which is indicated by the transmission symbol rate, also known as the Baud rate. Fig. 5(a) shows that by increasing the symbol rate, the effectiveness of the optimized BLSS techniques declines for the same number of calculation steps/span. The best performance is demonstrated at a 14 GBaud symbol rate with a Q-factor of 10.9 dB (BER ~ 2.25×10-4) using 10 calculation steps/span. The observation can explain this trend that at small steps/span, the signal waveform changes substantially over one step as the symbol rate is increased due to the impact of increased dispersion. It is inferred that more calculation steps are required for large data rates for optimum performance of the logarithmic step size, indicating a trade-off between data rate and complexity. The performance of different compensation techniques as a function of symbol rate is shown in Fig. 5(b).