The FASTER subsea cable connecting the US with Japan will be upgradeable to 2.5 times the capacity originally planned thanks to research by NEC and Google

NEC has said the spectral efficiency across the FASTER subsea cable system can be upgraded to 6 bits per second per hertz for a capacity of more than 26 terabits per second (Tbps) -- over two and a half times the capacity originally planned at no additional wet plant capex.

In joint research with Google, NEC said the tests made use of artificial intelligence (AI) and probabilistic shaping at a 64 Quadrature Amplitude Moderation (64 QAM) modulation.

"For the first time on a live cable, artificial intelligence was used to analyse data for the purpose of nonlinearity compensation (NLC). NEC developed an NLC algorithm based on data-driven deep neural networks to accurately and efficiently estimate the signal nonlinearity," NEC said.

"In doing so, the authors set a spectral efficiency-distance product record of 66,102b/s/Hz in a field trial performed together with live traffic neighbouring channels."

According to NEC's Submarine Network Division GM Toru Kawauchi, this approach utilises machine learning algorithms that can be used on any subsea cable system.

"The results demonstrate both an improvement in transmission performance and a reduction in implementation complexity," Kawauchi explained.

NEC said it would continue its AI-based research after achieving a capacity increase of around 15Gbps in every 100GHz of fibre bandwidth.

The 10,000km FASTER subsea cable system will also connect the west coast of the United States with Asia, landing in Japan and consisting of six fibre pairs and making use of 10Gbps wave technology.

The announcement followed NEC last year demonstrating speeds of 50.9Tbps across subsea cables of up to 11,000km on a single optical fibre through the use of C+L-band erbium-doped optical fibre amplifiers, amounting to speeds of 570 petabits per second-kilometre.

In order to attain the bandwidth, NEC researchers similarly developed a multi-level, linear, and non-linear algorithm to obtain an optimised 32 QAM or opt32 constellation with a higher limit for non-linear capacity specifically for transmission across subsea cables.

In March, it was also revealed that NEC had been signed to construct the 10,500km 144Tbps Southeast Asia Japan 2 cable (SJC2), which will have 11 landing stations in Singapore, Thailand, Cambodia, Vietnam, Hong Kong, China, South Korea, Taiwan, and Japan.

The SJC2 cable, which will be made up of eight pairs of optical fibre, is being built by a consortium including China Mobile International, Chunghwa Telecom, Chuan Wei, Facebook, KDDI, Singtel, SK Broadband, and VNPT.

NEC last year additionally commenced construction of three 100Gbps subsea cable links to provide connectivity to Palau, Yap, and Chuuk islands in partnership with Belau Submarine Cable Corporation and the Micronesian government, along with the 3,900km, 100Gbps Hong Kong-Guam subsea cable system back in 2016, due to be completed in the fourth quarter of 2019 with a design capacity of almost 50Tbps.

In November 2016, NEC also completed construction of the Asia-Pacific Gateway (APG) subsea cable between China, Hong Kong, Japan, South Korea, Malaysia, Taiwan, Thailand, Vietnam, and Singapore, which provides capacity of more than 54Tbps.

The APG fibre-optic submarine cable -- owned by a consortium of telecommunications carriers including China's China Telecom, China Unicom, and China Mobile; Japan's NTT Communications; South Korea's KT Corporation and LG Uplus; Singapore's StarHub; Taiwan's Chunghwa Telecom; Thailand's CAT; Malaysia's Global Transit Communications; and Vietnam's Viettel and VNPT -- stretches 10,900km across the region.

Telecommunications carriers and consortiums have been racing to build out subsea cable capacity across the Asia-Pacific region, driven by the rapid increase in data usage globally.

In addition to FASTER, APG, and SJC2, these cables include the Hawaiki Transpacific Submarine Cable System; Southern Cross Cable Network's NEXT cable; the Jupiter subsea cable being built by a consortium including Facebook, Amazon, SoftBank, NTT Com, PLDT, and PCCW; Vocus' Australia-Singapore Cable and North West Subsea Cable; the Trident cable; SubPartners' Indigo, being build with Google, Singtel, Telstra, AARNet, Indosat Ooredoo, and Alcatel Submarine Networks; Superloop's Hong Kong cable; Telstra's Hong Kong Americas (HKA) and the Pacific Light Cable Network (PLCN); Google's Japan-Guam-Australia (JGA) cable system; and the Australian government's Solomon Islands-Papua New Guinea subsea cable system.

ZDNet