Strange Xbox Signal Suspected of Jamming Wireless LANs
Microsoft's Xbox 360 game console can create a strong and strange signal that disrupts wireless
John Cox, Network World
Microsoft's popular Xbox 360 game console can create a
strong and strange signal on wireless LANs, according to IT staff at Morrisville State College.
It's not clear whether the signal disrupts the college's WLAN access points or students'
wireless notebooks. There is some anecdotal evidence, however, that it at least affects other
radios in the same 2.4GHz band.
Morrisville IT staff typically use Bluetooth headsets, which run in the 2.4GHz band, with their
cell phones when they troubleshoot problems on the spacious campus. "We had problems syncing
our headsets to our phone where this signal was strong," says Matt Barber, the college's
network administrator. A phone user had to physically touch the headset to the cell phone to
make the initial connection, he says.
There may be effects on the WLAN that the equipment itself, from Meru Networks, is
circumventing, according to Barber. Part of Meru's WLAN architecture employs software that
gives the access points more control over wireless-client transmission behavior than does the
software of some of Meru's rivals. An access point near a radiating Xbox may be compensating
for interference by in effect guiding a wireless laptop to send and receive when open spectrum
is available, essentially dodging around the Xbox signal.
Working with Meru, the small IT staff is planning to test soon the effect of multiple Xbox
consoles in a dorm with a large number of active notebook clients.
Network World has asked Microsoft to comment on the Xbox signal phenomenon, but the company was
not able to reply before this story was posted. We'll update this report as soon Microsoft
The latest version of the Xbox, the Xbox 360 Elite, went on sale earlier this year with a
120G-byte hard disk and a high-definition video interface.
Morrisville is a small college in rural New York state, taking its name from a nearby town. In
summer 2007, the college deployed a campuswide 802.11a/b/g WLAN based on equipment from Meru..
The plan was to replace those access points with Meru's new, two-radio devices that added
support for Draft 2 of 802.11n, the IEEE standard that boosts throughput from 22M to 25Mbps to
at least 150M to180Mbps. That replacement was just completed, creating the first large-scale
During the fall, Morrisville IT staff, working with Meru engineers and IBM, the network
integrator, detected an unusual signal in the 2.4GHz band. "We wanted to look at the [radio
frequency] environment in our dorms," Barber says. "We always thought we'd run into some
strange stuff [there] in the 2.4 range."
The signal was discovered using Cognio Spectrum Expert, from Cognio (recently bought by Cisco).
Spectrum Expert is RF-analysis software packaged with a WLAN adapter card that slots into any
laptop PC. (See our April 2007 Clear Choice Test of four WLAN protocol analyzers.) Among other
capabilities, Spectrum Expert identifies sources of radio energy in the 2.4GHz and 5GHz WLAN
bands, and identifies the cause, such as a brand of access point or a microwave oven.
"The signal really stood out," Barber says. "In some places it was so strong we thought it
might be affecting the air [that is, the radio environment] around it."
The Cognio software, however, was baffled by this new signal: "Unknown emitter" was the
classification. The signal shows up in the Cognio display as a kind of green-blizzard effect,
covering a large swath of the 2.4 band, Barber says. That means the signal "is jumping all over
the spectrum band," he says. In contrast, a nearby Meru access point shows up in the same scan
as a strong, stable yellow-red glow, almost like a sun. The green blizzard is shot through with
red dashes, which show, Barber says, that the signal at moments nearly rivals the access point
The mystery signal baffled the IT staff and Meru until Barber had a brainstorm: He brought in
his own Xbox 360 and plugged it in, and turned on the Cognio spectrum analyzer. Presto: The
same signal appeared.
Barber says the signal seems be created by the console's embedded 2.4GHz radio, which is used
to communicate with the handheld wireless controller -- the gizmo with the buttons that
manipulate a game running on the console. The Xbox also takes an optional Wi-Fi adapter, in the
form of an USB dongle, to connect to a WLAN access point.
Barber says his "best guess" at this point is that the embedded radio, not the USB adapter,
causes the signal. The signal is created even if the Xbox console is shut off: Just plugging
its AC adapter into an electrical outlet seems to trigger the radio to look for -- and keep
looking for -- a companion wireless controller. "It's even worse when you have multiple Xboxes
in an area," Barber says.
At one point, IT staff wrapped the console in a static discharge bag, the material used, for
example, to wrap and protect consumer electronics gear from static damage during shipment. The
same properties make it act like radio "blanket" to muffle a transmission. Sure enough, the
Cognio software showed a significant drop in the Xbox signal's strength.
The next step is more systematic testing. "We want to get several consoles together with a
bunch of WLAN clients, to create a busy [RF] environment, and do some measurements," Barber
says. "Are we seeing frames being dropped in the air, or people getting disconnected?"
Answering that question may be a bit more urgent, with Christmas looming, and the likelihood of
still more brand-new Xboxs and other wireless entertainment products turning up in January when