FPGA Implementation for 24.576-Gbit/s Optical PAM4 Signal Transmission with MLP-Based Digital Pre-Distortion

Area of Science:

• Optical Communications
• Digital Signal Processing
• Machine Learning Applications

Background:

• Lookup table (LUT) algorithms are standard for pre-distortion in intensity modulation/direct detection (IM/DD) systems.
• LUTs face storage limitations, restricting pattern length and nonlinear compensation effectiveness.
• Multilayer perceptrons (MLPs) offer a solution by predicting errors and generating pre-distorted signals with minimal computational resources.

Purpose of the Study:

• To implement and evaluate a multilayer perceptron-based digital pre-distortion (MLP-DPD) scheme for short-reach optical communication.
• To demonstrate the feasibility of MLP-DPD in overcoming storage limitations of traditional LUT algorithms.
• To achieve high-speed data transmission with effective nonlinear compensation in a real-time system.

Main Methods:

• An MLP-DPD scheme was implemented on a field-programmable gate array (FPGA).
• A 14.7456 GBaud pre-distorted pulse amplitude modulation 4-level (PAM4) signal was generated and transmitted over 20 km of standard single-mode fiber (SSMF).
• Signal processing at the receiver utilized the parallel constant modulus algorithm (PCMA).

Main Results:

• The system achieved a bit error rate (BER) below the 2.4 × 10^-2 threshold for soft-decision forward error correction (SD-FEC).
• A net transmission bit rate of 24.576 Gbit/s was successfully realized.
• The MLP-DPD approach demonstrated effective nonlinear compensation with limited computational resources.

Conclusions:

• MLP-DPD is a feasible and effective technique for nonlinear compensation in high-speed optical communication systems.
• This method overcomes the storage constraints of traditional LUTs, enabling improved performance.
• The implementation on an FPGA showcases the practical application of MLP-DPD in real-time optical systems.