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Computationally efficient fixed-state MLSD for 100G C-band dispersion-uncompensated IM/DD links.
Optics Express
|December 19, 2025
Summary
A new complexity-efficient maximum likelihood sequence detection (CE-MLSD) scheme reduces computational load in high-speed optical systems. This method maintains bit-error rate performance while significantly cutting multiplications for advanced modulation formats.
Area of Science:
- Optical Communications
- Signal Processing
- Digital Communications
Background:
- Maximum Likelihood Sequence Detection (MLSD) is crucial for mitigating inter-symbol interference (ISI) in high-speed intensity modulation and direct detection (IM/DD) systems.
- Digital noise-whitening post filters (PF) enhance MLSD performance but introduce significant computational complexity, scaling exponentially with filter order and modulation level.
Purpose of the Study:
- To propose a complexity-efficient MLSD (CE-MLSD) scheme that reduces computational complexity while maintaining performance in high-speed IM/DD systems.
- To enhance frequency-domain compensation by increasing post-filter taps and selectively retaining dominant states and symbol levels.
Main Methods:
- Developed a CE-MLSD scheme by optimizing state and symbol level retention.
- Increased the number of post-filter taps for improved frequency-domain compensation.
- Conducted a comparative analysis of computational complexity and bit-error rate (BER) performance against other MLSD schemes.
Main Results:
- CE-MLSD significantly reduces multiplication complexity compared to full-state MLSD: 91.67% for 100-Gb/s OOK, 99.79% for 120-Gb/s PAM-4, and 99.68% for 120-Gb/s PAM-6 over specified distances.
- Maintains comparable BER performance to full-state MLSD across different modulation formats and fiber lengths.
- Offers superior complexity reduction over Trellis Path-Limitation MLSD (TL-MLSD) and Fixed-State MLSD (FS-MLSD) for PAM-4 and PAM-6 signals.
Conclusions:
- The proposed CE-MLSD scheme effectively balances computational complexity and BER performance in high-speed IM/DD optical systems.
- CE-MLSD presents a viable solution for developing low-cost, high-performance C-band IM/DD systems with extended reach capabilities.
- This approach is particularly beneficial for advanced modulation formats like PAM-4 and PAM-6, enabling more efficient optical transmissions.
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