A Breakthrough for Speeding Satellite Feeds
An emerging data-coding technology could more than double bandwidth on satellite Internet connections, boosting service to developing countries, planes, and cruise ships—and fixing jerky, stop-and-start images from live video news feeds.
The work is described in a recent paper by researchers at MIT and its Lincoln Laboratory, together with colleagues at the Hamilton Institute in Maynooth, Ireland. They say that the gains could be as much as 20-fold in conditions where data losses are exceptionally large.
The advance could be most noticeable to television news watchers because it could end glitchy feeds from overseas correspondents. The satellite communications company Inmarsat plans to test the technology in 2014. “We are hoping it would give us clean video with fewer disruptions,” says Ammar Khan, whose title is design authority at the London-based company.
The technology involved is a variant on TCP (transmission control protocol), which governs basic Internet data delivery. Regular TCP delivers small packets of digital data in a way that confirms that they reach the intended destination intact and in the correct order. Built into TCP are systems for checking errors, requesting replacements for lost packets, and retrieving them.
But when this regular TCP is used on wireless networks, some bandwidth gets wasted on back-and-forth traffic to recover the inevitably dropped portions of a signal. This is a particularly large problem with satellites, because retrieving the lost parts requires round trips that can take a half a second or more.
The tweaked version of TCP being honed by the MIT group and colleagues instead sends mathematical functions describing multiple packets so that a receiving device, such as a satellite terminal, can solve for missing ones without having to refetch them. “You transfer more packets than what you normally would, but you don’t have to retransmit,” Khan says.
Inmarsat has more than 500,000 terminals around the world, installed on cruise ships, fishing boats, passenger jets, rooftops of office buildings (common for backup service), and on trucks and other equipment used by news organizations. Users could benefit in all of these contexts, Khan says.
The new coding technology has been shown to work in lab simulations, and in 2014 is expected to be subject to testing in an environment that emulates the long travel times and typical data losses found on satellites. If it shows promise, it would be tested on real satellites and considered for commercialization, Khan says.
Satellites tend to deliver communications to the very richest and the very poorest, but at a high cost. In places like rural Africa, where there are no fiber-optic connections, it can cost $2,000 to $3,000 per month to provide one megabit per month of satellite service, leaving people unable to afford much more than crucial text transmissions. Doubling bandwidth from satellites “would make a marked difference,” says Riyaz Bachani, CEO of Wananchi, an Internet provider in Nairobi, Kenya.
The rich have their problems, too. In certain constrained environments, like cruise ships, it can be challenging to give crowds of smartphone owners the bandwidth they’re accustomed to having in Boston or Palo Alto.
Satellite technology already includes some interesting methods to beef up service. But while the industry has deployed a number of technologies to improve “spectral efficiency,” companies have almost run out of tricks. “We’ve efficiently juiced a lot from all the other technologies we’ve used,” says Khan. “Network coding is a strong contender to boost further what we can do.”
The satellite transmission work expands on work Muriel Medard and colleagues at MIT have been pursuing in recent years to improve Wi-Fi and other terrestrial networks (see “A Bandwidth Breakthrough”) and even to improve efficiency on wired connections in data centers (see “A Smarter Algorithm Could Cut Energy Use in Data Centers by 35 Percent”).
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