To improve network throughput, scrap the ones-and-zeros system

Abandoning a signal’s traditional binary ones and zeroes will improve throughput in fiber, a Dutch PhD researcher says. By increasing the number of bit states from the traditional two — the one and zero — to four or eight, adding more light colors, and changing clock rates for each wavelength, throughput will be significantly increased, he claims.

“A higher number of levels implies more information per symbol, so four levels contain two bits of information, and eight levels contain three bits,” says Robbert van der Linden in an article on the Eindhoven University of Technology Department of Electrical Engineering website.

Therefore, you get up to three times the information in the same number of symbols, he says. The downside being it’s harder to decode, but it is doable, he claims.

Van der Linden, who also works part-time at fiber equipment supplier Genexis, says there are a number of other steps, too, that can improve passive optical networks (PONs) used often in fiber-to-the-home networks.

PONs cheaply hitch tens of homes to one fiber cable supplying the street or geographic area. However, they can produce signal degradation for the customers farthest from the central office due to extra splitters in the line and so on. General inefficiency also occurs with PONs. That’s because the ISP, in its attempt to rectify bad throughput for distant customers, over builds for nearby customers.

However, PONs are popular among ISPs. They require only one cable to a neighborhood and one central office transceiver. That’s cheaper, costs less to power, and takes up less real estate.

Van der Linden says the pipe simply needs to be better optimized. There’s wastage. One should, in fact, use the over-building — unnecessary for the nearby customers — to help the farther customers.

Something called “adaptive modulation” is the answer. One should “match the signal parameters to the available properties of the data channels,” he says.

Other ways to improve throughput

Improvements proposed, in addition to the aforementioned abandonment of binary, is to match dodgy signals that are harder to decode to customers close by who don’t need particularly clean signals, then create good signals, which are easier to decode, for the distant customers. By doing that, you optimize the pipe for everyone.

Throughput improves, too, as capacity goes up — everyone needs less time to communicate.

Van der Linden says one does this by making changes to the actual signal levels.

“Normally you would go for four or eight equidistant levels. But if you position the levels with unequal intermediate spaces, you open up larger gaps between pairs of levels that are closer together. The bit encoded within the large distance is easier to decode and thus can handle a worse signal quality,” he says.

He says that his “smarter” fiber optimization ideas, which produce better data rates, are based on technology already used in wireless, cable, and DSL.

Other proposals he makes in his thesis include more colors in the same fiber — that makes more data streams — and three different clock rates.

“Customers demand more bandwidth, but [they] don’t want to pay anything extra for it,” says Karl Tran, Manager Future Optical Systems at Genexis, in the article. “Robbert has achieved a great milestone: He devised ways to increase the capacity without introducing expensive techniques. The techniques he used are relatively simple.”