How to increase network bandwidth in the data center: introduced a new chip PSE-3

Nokia will unveil its new PSE-3 optical transceiver at an OFC conference next week in San Diego, providing data rates of 200 Gbit / s per wavelength for submarine cables, 400 Gbit / s in urban networks and 600 Gbit / s for links in data centers. Nokia representatives say that PSE-3 in some cases will increase network bandwidth by 65% ​​compared to existing solutions, while reducing power consumption by 60%.

We will tell you more about the technology under the cut.

/ photo Groman123 CC

How does the chip work?

The new chip is a commercial implementation of technologies tested by Nokia years earlier. In 2016, Nokia and scientists from the Munich Technical University worked on a joint project during which scientists were able to achieve a data transfer rate of 1 Tbit / s in the network of the Deutsche Telekom operator. And last year the Finnish company introduced in operation 250 Gigabit transatlantic fiber optic cable for Facebook. Its length was 5.5 thousand km, and it was stretched from New York to Ireland.

PSE-3 uses technology of probabilistic constellation shaping (PCS), with which the most effective (with less noise) phase / amplitude combination is selected. The essence of the method is that signal points with high amplitude are used less often than points with low amplitude. "Constellation" adapts to the conditions of the transmission channel, which increases the signal stability to distortion. PSE-3 uses quadrature modulation of QAM-64 - this means that the chip can choose from 64 constellation points for tuning.

According to Peter Winzer, director of optical systems at Nokia Bell Labs, the task was to form the constellations so as close to the Shannon limit . The formation is performed by the distribution matcher function, which is “wired” in the ASIC and makes sure that all the symbols of the QAM constellation meet with different probabilities.

By focusing energy on symbols with a lower amplitude while reducing bandwidth, the probabilistic conversion function gives the “square constellation” the shape of a Gaussian curve (an example can be found in WP Nokia on the fifth page at the link ) Thus, PSE-3 allows us to approach the Shannon limit closer than 0.3 dB, increasing spectral efficiency, while other modern high-performance optical interfaces and WDM systems operate “at a distance” of 1.5–2.5 dB.

/ photo Claus Rebler CC

Technology potential

Nokia has tested the technology in US and German networks. An experiment in the United States showed that PCS technology can increase network bandwidth by 68% and reduce the number of transponders needed by 35%, compared to 100G QPSK. Compared to 100G – 250G transceivers, the results were 25 and 25%, respectively. A similar test in Germany showed a 14% increase in bandwidth and a 30% reduction in the number of transceivers.

Nokia representatives and scientists at the University of Munich are convinced that in the future, PCS technology will automatically adapt to the traffic requirements and will provide even faster transfer of large sets of information. As for the PSE-3, then, presumably, the chip will appear on the market at the end of this year or at the beginning of 2019.

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