<http://www.wired.com/gadgets/wireless/news/2007/07/wifi_interference/>
Got Interference? Data-Crowding Problems Loom for Wi-Fi
Robert Lemos Email 07.17.07 | 2:00 AM
The airwaves in the city of Riverside, California, just got a lot more
crowded.
On Monday July 9, the city switched on its municipal wireless network,
delivering free internet service to more than three square miles of the
downtown area. According to MetroFi, the wireless service provider that
teamed up with AT&T to build the network, the ad-supported service
offers up to 512-kbps download speeds to each resident in the area
covered.
Yet, for many living in the inland empire's capital city, the free
service isn't a bonus, it's a burden. The new network adds even more
sources of interference to the already crowded wireless spectrum.
MetroFi installed 25 to 30 wireless nodes per square mile to cover the
downtown Riverside area. Because wireless signals in the most commonly
used Wi-Fi band of 2.4 GHz are scattered by buildings and trees,
MetroFi's wireless nodes could interfere with other wireless networks in
the area, and vice versa.
Craig Mathias, principal analyst and founder of wireless research firm
Farpoint Group, says such citywide Wi-Fi projects could overwhelm nearby
residential systems.
"We have definitely seen a negative impact from these systems," he says.
"But we just haven't been able to quantify that impact."
Interference on wireless networks will likely get worse before it gets
better. Sometimes, the most egregious offenders aren't nearby
residential networks or municipal Wi-Fi grids, but the myriad electronic
devices in people's homes. Poorly shielded microwave ovens leak radio
waves tuned to 2.45 GHz, the resonant frequency of water. Many cordless
phones operate in the 2.4-GHz band as well. Wireless keyboards,
Bluetooth devices, wireless security cameras and baby monitors can all
interfere with a Wi-Fi network.
"It's a worse problem for a consumer than it is for an enterprise,
because you have a lot more wireless gizmos in your space," says Neil
Diener, chief technology officer for wireless-solutions provider Cognio.
Most people don't notice interference problems unless the cacophony of
electronic signals causes their residential network connection to drop.
MetroFi, which has covered 77 square miles with wireless networks in the
San Francisco Bay Area, has received only five e-mail messages regarding
interference problems, the company said.
Diener says the low level of concern is because consumers typically
underutilize their wireless networks. For most, wireless is a way to
connect to the internet. While even the best residential broadband
speeds may reach 5 Mbps, today's wireless network equipment makers boast
speeds up to 54 Mbps for popular 802.11g equipment.
If the wireless network can maintain even slight connectivity, Wi-Fi
will outperform current broadband solutions, Diener says.
"It's like when your arteries are partially clogged, you don't know it
until you have a heart attack," he says.
As consumers push more bits over their wireless networks, the slowdowns
will likely become much more obvious.
Apple TV uses next-generation wireless networking technology, dubbed
802.11n, to shuffle multi-gigabyte video files to and from computers on
a home network. Cell phones that allow users to browse the internet and
even make calls using the local wireless network, such as BlackBerry
devices and the iPhone, are increasingly popular. Game consoles like the
PlayStation Portable allow players to connect to the internet and each
other using Wi-Fi.
The next-generation of Wi-Fi has both benefits and drawbacks in terms of
interference.
Wireless networks using the most popular protocols, known as 802.11b and
802.11g, use a part of the unlicensed radio spectrum in the 2.4-GHz band
by default. The next-generation 802.11n also uses the spectrum by
default. While 802.11n access points use multiple antennas to allow the
devices to cope with interference and improve range, many consumers will
be tempted to use a new feature that doubles the speed of the device --
at the cost of hogging double the amount of spectrum bandwidth.
That's a recipe for greater interference, says Farpoint Group's Mathias.
"That will cream the bandwidth," he says.
[snip]
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