Realization of real-time DSP for C-band PAM-4 transmission in inter-datacenter network.

We designed and realized real-time pulse amplitude modulation-4 (PAM-4) digital signal processing (DSP) including forward error correction (FEC) for a C-band inter-datacenter network. The PAM-4 DSP is intended to compensate for chromatic dispersion and provide dispersion tolerance. A decision feedback equalizer (DFE) and maximum likelihood sequence equalizer (MLSE) were employed for the dispersion compensation. A low-density parity check (LDPC) code was used to increase coding gain. The soft-decision Viterbi algorithm (SOVA) was adopted to provide probabilistic information to the LDPC code. For implementation in a real-time field programmable gate arrays (FPGAs), we employed fully parallelized structures. In the design, three LDPC cores were operated in parallel, and the equalizers were also operated with 128 PAM-4 symbols. With the DSP, we empirically proved the feasibility of 25 km transmission without error-floor sign, corresponding to a dispersion compensation capacity of 425 ps/nm. We confirmed 35 km ∼ 85 km error-free transmission for inter-datacenter network.

[1]  In-Ki Hwang,et al.  Low-Complexity Soft-Decision Viterbi Algorithm for IM/DD 56-Gb/s PAM-4 System , 2019, IEEE Photonics Technology Letters.

[2]  Qi Yang,et al.  Improving performance of mobile fronthaul architecture employing high order delta-sigma modulator with PAM-4 format. , 2017, Optics express.

[3]  G. Torfs,et al.  Real-Time 100 Gb/s NRZ and EDB Transmission With a GeSi Electroabsorption Modulator for Short-Reach Optical Interconnects , 2018, Journal of Lightwave Technology.

[4]  S. Fu,et al.  Transmission of 2 × 56 Gb/s PAM-4 signal over 100 km SSMF using 18 GHz DMLs. , 2016, Optics letters.

[5]  Shu Lin,et al.  Construction of Quasi-Cyclic LDPC Codes for AWGN and Binary Erasure Channels: A Finite Field Approach , 2007, IEEE Transactions on Information Theory.

[6]  Mengqi Guo,et al.  C-band 56-Gb/s PAM4 transmission over 80-km SSMF with electrical equalization at receiver. , 2019, Optics express.

[7]  S-R Moon,et al.  C-band PAM-4 signal transmission using soft-output MLSE and LDPC code. , 2019, Optics express.

[8]  Klaus Grobe,et al.  Demonstration of the First Real-Time End-to-End 40-Gb/s PAM-4 for Next-Generation Access Applications Using 10-Gb/s Transmitter , 2016, Journal of Lightwave Technology.

[9]  J. Huh,et al.  EML based real-time 112 Gbit/s (2 × 56.25 Gbit/s) PAM-4 signal transmission in C-band over 80 km SSMF for inter DCI applications , 2018, Optical Fiber Technology.

[10]  Radhakrishnan Nagarajan,et al.  Silicon photonics-based 100 Gbit/s, PAM4, DWDM data center interconnects , 2018, IEEE/OSA Journal of Optical Communications and Networking.

[11]  Frank R. Kschischang,et al.  Block-Interlaced LDPC Decoders With Reduced Interconnect Complexity , 2008, IEEE Transactions on Circuits and Systems II: Express Briefs.