Simplified layered MLSE for PAM4 short-reach optical interconnects

Area of Science:

• Optical communications
• Digital signal processing
• VLSI design

Background:

• High-speed optical interconnects are crucial for modern data centers and high-performance computing.
• Conventional Maximum Likelihood Sequence Estimation (MLSE) faces challenges in processing delay and hardware complexity for next-generation data rates.
• Pulse Amplitude Modulation with 4 levels (PAM4) is a key modulation scheme for achieving higher data rates.

Purpose of the Study:

• To propose a simplified layered Maximum Likelihood Sequence Estimation (MLSE) algorithm.
• To reduce processing delay and hardware resource utilization (multipliers, adders, comparators) in optical interconnects.
• To validate the performance of the proposed MLSE in a real-world high-speed optical transmission system.

Main Methods:

• Development of a novel simplified layered architecture for MLSE.
• Experimental validation using a 112-Gbit/s PAM4 optical transmission system over 2-km of standard single-mode fiber.
• Comparative analysis of the proposed MLSE against conventional MLSE in terms of bit error rate (BER), processing delay, and hardware resource count.

Main Results:

• The simplified layered MLSE achieved nearly identical bit error rate performance compared to the conventional MLSE.
• Processing delay was significantly reduced from 34 clock cycles to 7 clock cycles.
• Hardware resources were substantially reduced: multipliers by 93.6%, adders by 3.7%, and comparators by 67.2%.

Conclusions:

• The simplified layered MLSE effectively addresses the high-speed and high-efficiency demands of optical interconnects.
• The proposed method offers a significant reduction in processing delay and hardware complexity without compromising performance.
• This approach is a promising solution for future high-capacity optical communication systems.