Low-complexity non-integer fractionally spaced feed-forward equalization with half-symbol-spaced kernel estimation
Optics Letters
|May 15, 2026
Summary
A novel feed-forward equalizer (FFE) uses half-symbol-spaced kernel estimation (HSSKE) for efficient high-speed optical communication. This method reduces complexity while maintaining performance, improving receiver sensitivity and bit error rates in PAM-4 systems.
Area of Science:
- Optical Communications
- Signal Processing
Background:
- High-speed intensity modulation and direct detection (IM/DD) systems require efficient equalization techniques.
- Fractionally spaced equalizers (FS-FFE) are crucial for mitigating signal impairments in modern optical networks.
Purpose of the Study:
- To propose a low-complexity non-integer fractionally spaced feed-forward equalizer (FFE) utilizing half-symbol-spaced kernel estimation (HSSKE).
- To enable accurate, aliasing-free kernel estimation at 2 samples per symbol (sps) and efficient equalization below 2 sps.
Main Methods:
- Implementation of HSSKE for kernel estimation in a 1.2-sps FFE.
- Experimental validation on a 100-GBaud/λ PAM-4 system over 1-km and 2-km standard single-mode fibers (SSMFs).
- Integration with noise whitening filter (NWF) and maximum likelihood sequence estimation (MLSE) for advanced performance analysis.
Main Results:
- The 1.2-sps FFE with HSSKE outperformed the 1.2-sps FFE with symbol-spaced estimation (SSKE).
- Achieved equalization performance comparable to conventional 2-sps FFE with over 27% reduction in computational complexity.
- Demonstrated 0.9-dB receiver sensitivity improvement and BER reduction below HD-FEC thresholds when combined with NWF and MLSE.
Conclusions:
- The proposed HSSKE-based FFE offers a significant reduction in computational complexity for high-speed IM/DD systems.
- This approach provides a viable solution for achieving high performance at lower sampling rates, enhancing spectral efficiency.
- The integration with NWF and MLSE further boosts performance, meeting stringent forward error correction (FEC) requirements.
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