NEC and Google have tested probabilistic shaping techniques to adjust the modulation of optical transmission across the 11,000-km FASTER subsea cable linking the U.S. and Japan.
The companies have demonstrated that the FASTER open subsea cable can be upgraded to a spectral efficiency of 6 bits per second per hertz (b/s/Hz) in an 11,000km segment -- representing a capacity of more than 26 Tbps in the C-band, which is over 2.5X the capacity originally planned for the cable, for no additional wet plant capital expenditure. The achievement represents a spectral efficiency-distance product record of 66,102 b/s/Hz.
The field trial was performed with live traffic on neighboring channels.
The companies said their test used near-Shannon probabilistic-shaping at a modulation of 64QAM, and for the first time on a live cable, artificial intelligence (AI) was used to analyze data for the purpose of nonlinearity compensation (NLC). NEC developed an NLC algorithm based on data-driven deep neural networks (DNN) to accurately and efficiently estimate the signal nonlinearity.
"Other approaches to NLC have attempted to solve the nonlinear Schrodinger equation, which requires the use of very complex algorithms," said NEC's Mr. Toru Kawauchi, General Manager, Submarine Network Division. "This approach sets aside those deterministic models of nonlinear propagation, in favor of a low-complexity black-box model of the fiber, generated by machine learning algorithms. The results demonstrate both an improvement in transmission performance and a reduction in implementation complexity. Furthermore, since the black-box model is built up from live transmission data, it does not require advance knowledge of the cable parameters. This allows the model to be used on any cable without prior modeling or characterization, which shows the potential application of AI technology to open subsea cable systems, on which terminal equipment from multiple vendors may be readily installed."
Transpacific FASTER Cable Enters Service with 60 Tbps Capacity
FASTER is a 9,000km trans-Pacific cable connecting Oregon and two landing sites in Japan (Chiba and Mie prefectures). The system has extended connections to major hubs on the West Coast of the U.S. covering Los Angeles, the San Francisco Bay Area, Portland and Seattle. The design features extremely low-loss fiber, without a dispersion compensation section, and the latest digital signal processing technology.
Google will have sole access to a dedicated fiber pair. This enables Google to carry 10 Tbps of traffic (100 wavelengths at 100 Gbps). In addition to greater capacity, the FASTER Cable System brings much needed diversity to East Asia, writes Alan Chin-Lun Cheung, Google Submarine Networking Infrastructure.
Construction of the system was announced in August 2014 by the FASTER consortium, consisting of China Mobile International, China Telecom Global, Global Transit, Google, KDDI and Singtel.
