Low-complexity adaptive multipath interference and channel noise mitigation scheme based on optimized detection for...

Area of Science:

• Optical Communications
• Digital Signal Processing

Background:

• Bandwidth-limited intensity modulation and direct detection (IM/DD) systems face challenges from multipath interference (MPI) and channel noise.
• MPI and channel noise typically manifest in specific frequency bands, resembling bandstop filtering characteristics after equalization.

Purpose of the Study:

• To propose a low-complexity adaptive multipath interference and channel noise mitigation (AMCM) scheme for IM/DD systems.
• To enhance receiver digital signal processing (DSP) capabilities for improved signal quality.

Main Methods:

• The AMCM scheme utilizes optimized detection, integrating an adaptive bandpass filter (BPF) and a log-maximum a posteriori estimation with a lookup table-based fixed number of surviving states (LUT-based FS-MAP) decoder.
• The adaptive BPF targets MPI and channel noise based on their spectral distribution.
• The LUT-based FS-MAP decoder addresses intersymbol interference (ISI) introduced by the BPF.

Main Results:

• The AMCM scheme was implemented in an O-band 56-Gbaud IM/DD optical 4-level pulse amplitude modulation (PAM-4) system over 10-km standard single-mode fiber.
• The proposed scheme achieved enhanced signal-to-interference ratio (SIR) tolerance of 11 dB.
• The system reached a 7% hard-decision forward error correction threshold with low computational cost (three real-valued multiplications per symbol).

Conclusions:

• The developed AMCM scheme effectively mitigates MPI and channel noise in bandwidth-limited IM/DD systems.
• This work represents the first application of optimized detection for MPI mitigation in such systems.
• The scheme offers a practical solution for improving the performance of high-speed optical communication systems.