C-band PAM-4 signal transmission using soft-output MLSE and LDPC code

Area of Science:

• Optical Communications
• Digital Signal Processing
• Coding Theory

Background:

• C-band PAM-4 transmission systems face challenges with signal integrity and error correction.
• Integrating equalization and error correction codes is crucial for improving performance.

Purpose of the Study:

• To propose and experimentally validate a novel DSP scheme combining sMLSE and LDPC codes for enhanced C-band PAM-4 transmission.
• To evaluate the performance gains of the proposed sMLSE-LDPC scheme compared to conventional MLSE-RS systems.

Main Methods:

• Modification of MLSE to soft-output (sMLSE) using the Max-log BCJR algorithm.
• Integration of a low-overhead LDPC code with sMLSE.
• Experimental investigation in a 56 Gb/s C-band PAM-4 system.
• Performance comparison with MLSE-RS code, including analysis of burst errors and the effect of an interleaver.

Main Results:

• The sMLSE-LDPC scheme achieved an additional optical signal-to-noise ratio (OSNR) gain of 0.6 dB to 2.1 dB compared to MLSE-RS.
• The OSNR gain is influenced by burst errors caused by power fading.
• Employing an interleaver improved the relative OSNR gain to 1.6 dB - 2.1 dB by mitigating burst errors.
• Successful experimental demonstration of 30 km transmission at 56 Gb/s PAM-4 in the C-band using the proposed scheme with an interleaver.

Conclusions:

• The proposed sMLSE-LDPC scheme offers significant performance improvements for C-band PAM-4 systems.
• The integration of sMLSE with LDPC codes, particularly with an interleaver, effectively combats burst errors and enhances transmission performance.
• This approach enables robust and high-speed optical communication over extended distances.