Google and NEC show the way to triple subsea fibre capacity

15 May 2018 | Alan Burkitt-Gray

Google and NEC have doubled the performance of the transpacific Faster cable linking Taiwan to Oregon, and believe they can triple it.

The 10,000km cable was originally designed to carry traffic at 2 bits/second/hertz, say the companies, but using artificial intelligence (AI) techniques they increased spectral efficiency first to 3b/s/Hz and then to 4b/s/Hz – twice the original design specification.

Toru Kawauchi, general manager of NEC’s submarine network division, said: "This approach sets aside those [previous] deterministic models of nonlinear propagation, in favour of a low-complexity black-box model of the fibre, generated by machine learning algorithms."

Google and NEC tested the performance in a field trial performed together with live traffic neighbouring channels. They claim a spectral efficiency-distance product record of 66,102b/s/Hz. It the trial it carried live traffic from Google data centres.

NEC has also carried out offline field trials over dark fibres with even more promising results. They used fibre of the same length and achieved spectral efficiency of 5.68b/s/Hz and made other measurements that promise 6.06b/s/Hz – three times the original design specification of the Faster cable. NEC said it believes 6b/s/Hz is a "realistic target".

Kawauchi said: "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."

The team achieved this result using a technique called probabilistic-shaping which achieved a performance close to the theoretical maximum as predicted by Claude Shannon, the Nobel prize-winning Bell Labs mathematician who is known as the father of information theory for his work in the 1940s and 1950s.

"For the first time on a live cable, AI was used to analyse data for the purpose of nonlinearity compensation," said NEC in a statement.

"Other approaches to NLC have attempted to solve the nonlinear Schrödinger equation, which requires the use of very complex algorithms," said Kawauchi. This is a technique named after another Nobel prize-winner, Erwin Schrödinger.

Kawauchi added: "This allows the model to be used on any cable without prior modelling or characterisation, which shows the potential application of AI technology to open subsea cable systems, on which terminal equipment from multiple vendors may be readily installed."

The companies published their results in a scientific paper (PDF) authored by three Google scientists and six from NEC.

Topics: NEC, subsea, Google, Faster, Shannon, Schrödinger, Kawauchi