Select your localized edition:

Close ×

More Ways to Connect

Discover one of our 28 local entrepreneurial communities »

Be the first to know as we launch in new countries and markets around the globe.

Interested in bringing MIT Technology Review to your local market?

MIT Technology ReviewMIT Technology Review - logo


Unsupported browser: Your browser does not meet modern web standards. See how it scores »

{ action.text }

Wireless Lookout
Fast handoff for Wi-Fi networks

Context: People routinely access the Internet via the tens of thousands of Wi-Fi access points dotting airports, university campuses, cafés, and other public places. But a Wi-Fi device can connect to an access point only if it is close by—usually within 100 meters. When a device moves beyond the signal range of one access point, it is “handed off” to a nearer one, a process that disrupts data flow. For someone making a phone call over a Wi-Fi phone or watching live streaming multimedia, a one-second delay during handoff can be highly irritating. Ishwar Ramani and Stefan Savage of the University of California, San Diego, have developed a new approach, called SyncScan, that allows faster handoffs.

Methods and Results: Right now, a Wi-Fi device searches for a new access point only after the signal quality from the one it’s using degrades markedly. Then, the device scans all available wireless channels for beacons broadcast by access points, leaving little bandwidth for other incoming data.

With SyncScan, a Wi-Fi device regularly records the signal strengths of other channels, but it checks them only at the precise times that they are scheduled to transmit beacons. Such timing avoids needless channel switching, so the device receives more of the data being sent to it. It also makes better-timed and better-placed handoffs. In a prototype—a laptop computer running the popular Internet-telephony program Skype—the delay during handoff was reduced a hundredfold to only a few milliseconds. The algorithm is expected to work for all Wi-Fi devices.

Why it Matters: Internet telephony and streaming multimedia are emerging as hot applications in Wi-Fi networks. Wi-Fi phones already exist in Japan and are expected in the United States by this spring, but long handoff delays will discourage their adoption. SyncScan shrinks the handoff delay without the need for hardware upgrades or changes to IEEE 802.11, the most widely deployed standard for wireless networks. Though SyncScan is still not perfectly synchronized, it promises to greatly improve the quality, convenience, and value of communication in Wi-Fi networks.

Source: Ramani, I., and S. Savage. 2005. SyncScan: practical fast handoff for 802.11 infrastructure networks. Proceedings of IEEE Infocom 2005 (in press).

0 comments about this story. Start the discussion »

Tagged: Computing

Reprints and Permissions | Send feedback to the editor

From the Archives


Introducing MIT Technology Review Insider.

Already a Magazine subscriber?

You're automatically an Insider. It's easy to activate or upgrade your account.

Activate Your Account

Become an Insider

It's the new way to subscribe. Get even more of the tech news, research, and discoveries you crave.

Sign Up

Learn More

Find out why MIT Technology Review Insider is for you and explore your options.

Show Me