研究目的
To investigate a soft-decision Viterbi algorithm (SOVA) combined with low-density parity check (LDPC) to achieve high chromatic dispersion tolerance and alleviate the high OSNR requirement in pulse amplitude modulation 4-level (PAM-4) systems, with a focus on reducing complexity compared to maximum likelihood sequence equalizer (MLSE).
研究成果
The proposed non-binary SOVA algorithm achieves lower complexity and better BER performance (0.3 dB OSNR gain over conventional SOVA at BER 10^-6) in IM/DD PAM-4 systems, making it suitable for high-speed optical fiber communication with improved chromatic dispersion tolerance and reduced OSNR requirements. Future work could explore applications in higher modulation formats and further optimizations.
研究不足
The algorithm may have performance degradation compared to Max-log-MAP in dispersive channels (about 0.5 dB difference), and its effectiveness in higher modulation formats beyond PAM-4 is not fully explored. The experimental setup is limited to specific transmission distances and data rates, and the complexity reduction might not scale optimally for all scenarios.
1：Experimental Design and Method Selection:
The study involves designing a non-binary SOVA algorithm for IM/DD PAM-4 systems using LDPC as an FEC algorithm. The algorithm combines conventional SOVA and hard decision VA to reduce complexity, using one competing path per state and time index for reliability updates, and generates reliability scalars instead of vectors.
2：Sample Selection and Data Sources:
A 56 Gbps PAM-4 system is tested over transmission distances of 20 km and 30 km single-mode fiber (SSMF), with data generated from a 2^15-1 pseudo-random binary sequence (PRBS15).
3：5). List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Equipment includes a laser diode (LD), erbium-doped fiber amplifier (EDFA), variable optical attenuator (VOA), and components for optical fiber communication.
4：Experimental Procedures and Operational Workflow:
In transmitter DSP, data is encoded with LDPC or RS, interleaved, mapped to Gray-coded PAM-4, and transmitted. At receiver, timing recovery is done using Muller-Müller algorithm, followed by DFE (25-tap FFE and 1-tap FBE), SOVA equalization with constraint memory of 2, de-interleaving, and FEC decoding with up to 8 iterations for LDPC.
5：Data Analysis Methods:
Bit error rate (BER) is measured as a function of optical signal-to-noise ratio (OSNR) and compared across different algorithms (e.g., proposed SOVA, Max-log-MAP, conventional SOVA variants).
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