October 22, 2012

Coded TCP enables ten to twenty times more bandwidth

Technology Review - Academic researchers have improved wireless bandwidth by an order of magnitude—not by adding base stations, tapping more spectrum, or cranking up transmitter wattage, but by using algebra to banish the network-clogging task of resending dropped packets. The practical benefits of the technology, known as coded TCP, were seen on a recent test run on a New York-to-Boston Acela train, notorious for poor connectivity. Medard and students were able to watch blip-free YouTube videos while some other passengers struggled to get online.

By providing new ways for mobile devices to solve for missing data, the technology not only eliminates this wasteful process but also can seamlessly weave data streams from Wi-Fi and LTE.

Testing the system on Wi-Fi networks at MIT, where 2 percent of packets are typically lost, Medard's group found that a normal bandwidth of one megabit per second was boosted to 16 megabits per second. In a circumstance where losses were 5 percent—common on a fast-moving train—the method boosted bandwidth from 0.5 megabits per second to 13.5 megabits per second. In a situation with zero losses, there was little if any benefit, but loss-free wireless scenarios are rare.

The technology transforms the way packets of data are sent. Instead of sending packets, it sends algebraic equations that describe series of packets. So if a packet goes missing, instead of asking the network to resend it, the receiving device can solve for the missing one itself. Since the equations involved are simple and linear, the processing load on a phone, router, or base station is negligible, Medard says.

Whether gains seen in the lab can be achieved in a full-scale deployment remains to be seen, but the fact that the improvements were so large suggests a breakthrough.

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