Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Faster handoff between Wi-Fi networks promises near-seamless 802.11 roaming

14.04.2005


Road warriors may no longer have to stay put in an airport lounge or Starbucks to access the high-speed Internet via an 802.11 Wi-Fi network. Thanks to software developed by two computer scientists at the University of California, San Diego, the time it takes to hand off from one Wi-Fi wireless network to the next can be dramatically shortened -- overcoming a major obstacle in Wi-Fi roaming.



Jacobs School of Engineering professor Stefan Savage and graduate student Ishwar Ramani have a patent pending on the basic invention behind SyncScan, a process to achieve practical, fast handoff for 802.11 infrastructure networks. Their study will be published in the Proceedings of the IEEE InfoCom 2005.

"Wi-Fi offers tremendous speeds if you stay in one place or at least within 100 meters of the same access point," said Savage, an assistant professor in the Computer Science and Engineering department and academic participant in the California Institute for


Telecommunications and Information Technology. "SyncScan is a handoff algorithm which can cut the time it takes to switch from one Wi-Fi access point to another by a factor of a hundred over existing solutions. This is a requirement for demanding applications like Voice over Wi-Fi [VoWi-Fi], where even short interruptions can disrupt the illusion of continuous connectivity." Savage notes that SyncScan also allows mobile devices to make better handoff decisions and therefore improve signal quality overall.

At present, Wi-Fi handoffs are cumbersome and time-consuming. Not until the access-point signal weakens substantially and begins losing packets of data does a Wi-Fi-enabled laptop, PDA or mobile phone begin scanning for a stronger signal. At that point, it broadcasts requests on all channels to find nearby access points. The result: a delay of up to one second, during which any packets may be lost. That may not seem inordinate when downloading data, but it can be unacceptable if the user is trying to listen to Internet radio, watch a streaming movie trailer or talk on a Wi-Fi phone.

"Today most Wi-Fi users accept being tethered to a single location in exchange for the broadband speeds that Wi-Fi offers," said Ph.D. candidate Ramani. "But increasingly they want to be able to make Voice of IP (VoIP)phone calls or stream multimedia while commuting or on the move, and a one-second disruption can seem like an eternity."

The SyncScan solution proposed by Savage and Ramani is a method to continuously monitor the proximity of nearby 802.11 access points. Instead of looking for surrounding access points just when the current signal is running low, a Wi-Fi device with SyncScan regularly checks signal strengths nearby - but only for very short periods of time. These times are picked to precisely coincide with regularly scheduled "beacon" messages sent by all standard Wi-Fi access points. The process eliminates the current need to start from scratch when looking for a stronger signal, and replaces the long scanning delay with many small delays that are imperceptible to the user.

To test their SyncScan algorithm, the researchers used a laptop running a voice application while walking between two areas of the UCSD campus served by neighboring Wi-Fi access points. "We used a popular VoIP called Skype which uses UDP [user datagram protocol] packets exchanged between two clients for voice communication," explained Savage. "Using SyncScan with a measurement interval of 500 millseconds, handoff delay was virtually imperceptible - roughly 5 milliseconds. Repeating the tests without SyncScan, the average handoff time was 450 milliseconds, but ranging up to a full second in some cases."

The researchers also observed a big difference in the number of lost data packets that can contribute to loss of data or voice dropout. Zero packets were dropped using the SyncScan algorithm in the UCSD tests, compared to substantial packet losses using current technology. "That is because the overhead of scanning for nearby base stations when the current signal weakens is routinely over 250 milliseconds, during which incoming packets are dropped," said Ramani. "We expect that the same improvements can be achieved on most Wi-Fi devices and using most applications, not just voice." SyncScan is also economical, because it can be deployed incrementally and implemented in software without requiring any changes to the 802.11 standard or any hardware upgrades.

Just over 110,000 VoWi-Fi handsets were sold in 2004, mostly in Japan. Vonage is set to roll it out commercially in the U.S. later this spring as an add-on to its popular VoIP service, and sales of dual-use phones incorporating both cellular and VoWi-Fi could reach $3 billion by 2009, according to a study by Infonetics Research.

Doug Ramsey | EurekAlert!
Further information:
http://www.ucsd.edu

More articles from Information Technology:

nachricht Drones can almost see in the dark
20.09.2017 | Universität Zürich

nachricht World first: 'Storing lightning inside thunder'
18.09.2017 | University of Sydney

All articles from Information Technology >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

Im Focus: Quantum Sensors Decipher Magnetic Ordering in a New Semiconducting Material

For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.

Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...

Im Focus: Fast, convenient & standardized: New lab innovation for automated tissue engineering & drug

MBM ScienceBridge GmbH successfully negotiated a license agreement between University Medical Center Göttingen (UMG) and the biotech company Tissue Systems Holding GmbH about commercial use of a multi-well tissue plate for automated and reliable tissue engineering & drug testing.

MBM ScienceBridge GmbH successfully negotiated a license agreement between University Medical Center Göttingen (UMG) and the biotech company Tissue Systems...

Im Focus: Silencing bacteria

HZI researchers pave the way for new agents that render hospital pathogens mute

Pathogenic bacteria are becoming resistant to common antibiotics to an ever increasing degree. One of the most difficult germs is Pseudomonas aeruginosa, a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Molecular Force Sensors

20.09.2017 | Life Sciences

Producing electricity during flight

20.09.2017 | Power and Electrical Engineering

Tiny lasers from a gallery of whispers

20.09.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>