Graduate students at the MIT Computer Science and Artificial Intelligence Laboratory showed off their latest research at the university's Wireless retreat on Monday, outlining software-defined MIMO, machine-generated TCP optimization, and a localized wireless networking technique that works through sound.
Swarun Kumar's presentation on OpenRF – a Wi-Fi architecture designed to allow multiple access points to avoid mutual interference and focus signals on active clients – detailed how commodity hardware can be used to take advantage of features otherwise restricted to more specialized devices.
There were several constraints in the 802.11n wireless standard that had to be overcome, Kumar said, including a limitation on the total number of bits per subcarrier signal that could be manipulated, as well as restricting that manipulation to one out of every two such signals.
Simply disabling the Carrier Sense restrictions, however, proved an incomplete solution.
“Access points often send these beacon packets, which are meant for all clients in a network … you cannot null them at any point if you're a client. Unfortunately, these packets will now collide" in the absence of Carrier Sense, he said.
The solution – which involved two separate transmit queues – enabled OpenRF to automatically apply its optimal settings across multiple access points, distributing the computational workload across the access points, rather than having to rely on a beefy central controller.
Kumar said the system can boost TCP throughput by a factor of 1.6 compared to bare-bones 802.11n.
Keith Winstein attacked the problem of TCP throughput slightly differently, however. Using a specialized algorithm called Remy – into which users can simply input network parameters and desired performance standards – he said that networks can essentially determine the best ways to configure themselves on their own.
“So these are the inputs, and the output is a congestion control algorithm,” he said. “Now this is not an easy process – this is replacing a human protocol designer. Now, it costs like $10 to get a new protocol on Amazon EC2.”
Remy works via the heuristic principle of concentrating its efforts on the use cases where a small change in the rules results in a major change in the outcome, allowing it to optimize effectively and to shift gears quickly if network conditions change.
“Computer generated end-to-end algorithms can actually outperform human generated in-network algorithms, and in addition, human generated end-to-end algorithms,” said Winstein.
Even though Remy wasn't designed or optimized to handle wireless networks, it still handily outperforms human-generated competition, he added.
Peter Iannucci is a researcher looking into highly localized ways of providing wireless Internet, which he refers to as room area networks. Having dismissed a number of technologies as insufficient – Bluetooth was too clunky, NFC had limited uptake – he eventually settled on sound.
Iannucci's acoustic network – which he has dubbed Blurt – uses high-frequency sounds to transmit the ones and zeroes of a network connection. It's well-suited for a network confined by design to a small space.
“Acoustic networks provide great low-leakage properties, since doors and walls are intentionally sound-absorbent,” he said. “[They] work over moderate distances, using existing devices, and they don't require any setup for ad hoc communications.”
Iannucci acknowledges that Blurt isn't without its problems. Given that sound waves move about a million times slower than radio waves, speed is an issue – he said that Blurt can handle about 200 bits per second when using frequencies inaudible to humans, with more speed possible only at the cost of an audible whirring chirp, reminiscent of old telephone modems.
But that's really not the point – the idea would be more to do things like verify users of a business' free Wi-Fi are actually sitting in the restaurant, or any other tasks involving heavily location-dependent network services.
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