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Wednesday, November 14, 2012

New WiFi protocol boosts congested wireless network throughput by 700%

Engineers at NC State University (NCSU) have discovered a way of boosting the throughput of busy WiFi networks by up to 700%. Perhaps most importantly, the breakthrough is purely software-based, meaning it could be rolled out to existing WiFi networks relatively easily — instantly improving the throughput and latency of the network.

As wireless networking becomes ever more prevalent, you may have noticed that your home network is much faster than the WiFi network at the airport or a busy conference center. The primary reason for this is that a WiFi access point, along with every device connected to it, operates on the same wireless channel. A channel is basically a single-lane road, a lot like an electrical (copper wire) bus. Each channel, depending on the wireless technology being used, has a maximum bandwidth (say, 100 megabits per second), with that bandwidth being distributed between all connected devices.

At home, you might have exclusive use of that road, meaning you can drive as fast as you like and suck up every last megabit — but at a busy conference center, you are fighting tens or hundreds of people for space. In such a situation, your bandwidth allocation rapidly dwindles and your latency quickly climbs. This single-channel problem is also compounded by the fact that the road isn’t just one-way; the access point also needs to send data back to every connected device.

In short, WiFi networks have good throughput and low latency up until a point — and then they very quickly degrade into a horrible mess where no one can use the network properly. If the channel becomes congested enough that the access point can no longer send out data, then the show’s over, basically.

To solve this problem, NC State University has devised a scheme called WiFox. In essence, WiFox is some software that runs on a WiFi access point (i.e. it’s part of the firmware) and keeps track of the congestion level. If WiFox detects a backlog of data due to congestion, it kicks in and enables high-priority mode. In this mode, the access point gains complete control of the wireless network channel, allowing it to clear its backlog of data. Then, with the backlog clear, the network returns to normal.

We don’t have the exact details of the WiFox scheme/protocol (it’s being presented at the ACM CoNEXT conference in December), but presumably it switches between normal and high priority states very rapidly. If we use the single-lane road analogy, WiFox is basically playing the role of a traffic policeman — allowing data to flow freely in one direction for a while, and then reversing the flow. Presumably the trick is designing an algorithm that is capable of detecting congestion very rapidly, and designing a traffic cop that switches priority for exactly the right amount of time to clear the backlog.

All told, the NCSU researchers report that their testbed — a single WiFi access point with 45 connected devices — experienced a 700% increase in throughput. Exact figures aren’t given, but if we’re talking about a modern 802.11n network, we’re probably looking at a jump from around 1Mbps to around 7Mbps. Furthermore, latency is also decreased by 30-40%. There is no word when WiFox might be deployed commercially, but considering it could be rolled out as a firmware update it will hopefully be rather soon.


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