Today's wireless communication networks consist of huge numbers of scattered transmitters with limited range. While this "mesh" of WiFi and cellular technology makes for good coverage, these networks occasionally fall short of providing seamless roaming and successful handoffs.
This happens for a variety of reasons, including protocol errors, congestion, and interference. Still, when you drop a cell-phone call in a moving car or lose a WiFi connection while walking from one conference room to another, you don't offer much empathy for the network.
Recognizing the poor quality of experience, Researchers at MIT have developed a set of new communications protocols that use information about a portable device's movement to improve handoffs. Newer phones sport built-in motion sensors, such as GPS receivers, accelerometers and, increasingly, gyros, all of which provide information about the devices' trajectory and velocity.
In experiments on MIT's campus-wide Wi-Fi network, the researchers discovered that their protocols could often, for users moving around, improve network throughput (the amount of information that devices could send and receive in a given period) by about 50 percent.
The researchers — all from the Computer Science and Artificial Intelligence Laboratory — used motion detection to improve four distinct communications protocols:
Protocol 1- Governs the smart phones selection of the nearest transmitter
"Let's say you get off at the train station and start walking toward your office," Professor Hari Balakrishnan says in an MIT news release. "What happens today is that your phone immediately connects to the WiFi access point with the strongest signal. But by the time it's finished doing that, you've walked on, so the best access point has changed. And that keeps happening."
By contrast, Balakrishnan explains, the new protocol selects an access point on the basis of the user's inferred trajectory. "We connect you off the bat to an access point that has this trade-off between how long you're likely to be connected to it and the throughput you're going to get," he says.
In their experiments, the MIT researchers found that, with one version of their protocol, a moving cell phone would have to switch transmitters 40 percent less frequently than it would with existing protocols. A variation of the protocol improved throughput by about 30 percent.
Protocol 2 - Governs a phone's selection of bit rate
When a device is in motion, the available bandwidth is constantly fluctuating, so selecting a bit rate becomes more difficult. Because a device using the MIT protocol knows when it's in motion, it also knows when to be more careful in choosing a bit rate. In the researchers' experiments, the gains in throughput from bit rate selection varied between 20 percent and 70 percent but consistently hovered around 50 percent.
Protocol 3 - Governs the behavior of the wireless base stations
Ordinarily, a base station knows that a device has broken contact only after a long enough silence. In the meantime, the base station might try to send the same data to the device over and over, waiting forlornly for acknowledgment and wasting time and power. But with information about the device's trajectory, the base station can make an educated guess about when it will lose contact.
Protocol 4 - Uses motion data to determine routing procedures for networks of wirelessly connected cars
A little out of left field, but the team is also involved with MIT's CarTel project, which seeks to use information technology to make driving safer and more efficient. The relative position of cars are constantly changing, so this protocol could help in the dissemination of information about traffic and road conditions.
The team demonstrated their work recently at the Eighth Usenix Symposium on Networked Systems Design and Implementation.
Source: MIT News