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Enhanced Tomlinson-Harashima precoding and adapted likelihood-based radius-directed equalization for transmitter-side
Optics Express
|August 14, 2026
Summary
This study introduces an enhanced Tomlinson-Harashima precoding (THP) and likelihood-based selection radius-directed equalization (LBS-RDE) to overcome bandwidth limitations and noise in high-speed optical communication systems. The new method improves sensitivity and ensures stable performance over dynamic channels.
Area of Science:
- Optical Communications
- Signal Processing
- High-Speed Data Transmission
Background:
- Bandwidth-intensive applications necessitate high-baud-rate transmission, but transmitter-side bottlenecks and equalization-enhanced high-frequency noise (EEHN) degrade performance.
- Conventional Tomlinson-Harashima precoding (THP) struggles with residual EEHN and unstable tracking in dynamic channels due to limitations in mitigating precursor inter-symbol interference (ISI) and reliance on training sequences.
Purpose of the Study:
- To resolve limitations in conventional THP and adaptive equalizers (AEQs) for faster-than-Nyquist (FTN) systems operating over dynamic optical channels.
- To propose an enhanced THP scheme to suppress EEHN and an LBS-RDE scheme for stable receiver-side equalization in dynamic environments.
Main Methods:
- Developed an enhanced THP at the transmitter to suppress EEHN and precursor ISI.
- Implemented a likelihood-based selection (LBS) radius-directed equalization (RDE) scheme at the receiver, adapted for THP-expanded constellations.
- Validated the proposed scheme through simulations and experiments under static and dynamic channel conditions, including varying rotation of state of polarization (RSOP).
Main Results:
- The enhanced THP achieved a 1 dB sensitivity gain over conventional THP under static conditions with a bandwidth-constrained transmitter.
- Under dynamic channels (500 krad/s RSOP), the proposed scheme operated reliably, unlike conventional methods that failed to converge or suffered degradation.
- The proposed scheme demonstrated significant sensitivity improvements: 1.5 dB at 500 krad/s and 3.8 dB at 1000 krad/s RSOP.
Conclusions:
- The proposed enhanced THP and LBS-RDE scheme effectively suppresses EEHN and ensures stable operation in bandwidth-limited FTN systems over dynamic channels.
- This approach provides a comprehensive solution for improving the performance and reliability of high-speed optical communication systems facing practical channel impairments.
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