Bluetooth is a wireless bully
(go to Canadian version)

By Andy Walker,

Beware of burritos cooking in a microwave. They disrupt wireless data transmission.

I'm not kidding.

Microwaves emit radio waves in the same wireless spectrum as cordless phones, Bluetooth devices, wireless local area networks and garage door openers.
In fact all these technologies could all disrupt each other.

The biggest culprit, however, is Bluetooth. In fact, it's a wireless bully that's going to beat up severely on a wireless local area network technology called 802.11b or Wi-Fi.
"It will be (a problem) that builds up over time," said Jeff Reed, director of the mobile and portable radio research group at Virginia Tech.

"We've got a big boat called Titanic headed toward an iceberg and we better start turning it now."

To understand why it is a problem, a quick primer is in order.

Bluetooth is a new wireless technology that promises to make life simpler. Within the next two years, the little chips will be built into almost every gadget. It will enable them to connect to any other gadget so they can share information and resources. It will also eliminate wires between devices.

Wi-Fi, on the other hand, is used to connect notebooks and PCs to a computer network. Businesses and ambitious homeowners use it to connect multiple personal computers together without wires so they can share data, printers and fast Internet connections. It transmits data wirelessly at up to 11 Megabits per second with an actual transmission rate of about 7 Mbps.

When a Bluetooth device comes too close to a Wi-Fi gateway it starts to cause interference.

"Bluetooth jumps onto the wireless LAN frequency and can it shut it down to almost unusable level," said Mark Mastalir, spokesperson at Mobilian Corp., one of the wireless technology companies looking for a solution to the problem.

To understand how this happens, here's how the 2.4 GHz band works.
Think of this part of the radio spectrum as a pipe with dozens of phone wires in it. When data is sent on one of these imaginary phone wires, the transmitting device grabs a channel and sends data down it. There are actually 83.5 channels in the 2.4 GHz band.
Bluetooth uses 79 of these channels. Wi-Fi uses 22. Inevitably, there is some crossover.
Wi-Fi hops channels twice a second and checks to see if a channel is in use before using it. It's the Miss Manners of the 2.4 GHz band.

Meanwhile, Bluetooth channel hops 1,600 times a second and doesn't check to see if a channel is in use before it leaps onto it.

"Bluetooth is rude and robust and 802.11b is very polite," said Reed.
Bluetooth is hopping all over the spectrum, like an over-sugared six-year-old. It doesn't look before it leaps. If it picks a channel that Wi-Fi is already talking on, it just talks over top of the existing transmission. At the other end of the channel, the Wi-Fi receiver can't make head or tail of what was being sent. When this happens, Wi-Fi is smart enough to scale back its transmission and tries again at a slower speed.

So what does it mean to you?

Let's say your computer uses a Wi-Fi wireless network to share an Internet connection. Perhaps you're using it to download an important document or you are watching video via a Webcast. When your colleague waltzes in with her Bluetooth-enabled handheld computer and starts to synchronize data wirelessly with a PC, your connection to the Internet could become painfully slow. In the case of streaming video, you'll go from moving pictures to perhaps a slideshow or you may just lose the whole connection.
If a group of Bluetooth-equipped kids comes into the Starbucks where you are surfing the Internet using their Wi-Fi network, say goodbye to your very important connection to www.streamingsquirrels.com.

Of course, to wreak havoc, the Bluetooth gadget has to come within about three meters (10 feet) of the Wi-Fi gateway, normally a chocolate-box-sized appliance hung from the ceiling or stashed on a desktop.

But as millions of these devices flood the market, it's plausible that any one person could have three or more Bluetooth devices on their person at once. Crowd Bluetooth-enabled people into a Wi-Fi-enabled building and suddenly, there are hundreds of wireless misfits dancing all over the wireless LAN's business.
The wireless industry is aware of the potential problem, though there are varying opinions to its severity.

"It'll be kind of like driving along with a cellphone - going through good and bad areas of reception. But you're moving fast enough that you're in and out of the bad spots before you notice," explained David Quinn, president and CEO of Kaval Wireless Technologies, a company that deploys indoor wireless networks.
However, Reed fields a call a day from the members of the wireless industry who are concerned about the issue.

So what's to be done? One suggestion is to engineer the next version of Bluetooth to behave better. That would require more complex manufacturing and perhaps drive up the price of the technology. That's not good, given that manufacturers are having a hard time getting first generation chips to the $5 sweet spot the market needs for mass adoption of the technology.

The second generation of the Bluetooth standard, due out later this year, may also address the issue, though Lee Warren, chair of the OFDM Forum, a wireless technologies trade association, is not convinced by work done so far: "There's some optimism but I haven't seen any tangible results as yet."

The logical solution is to move Wi-Fi off the 2.4 GHz band into another frequency. Curiously, that's what was planned, anyway. Network experts want to crank up the bandwidth for wireless LANs so that it can better transmit multimedia content. Think wireless distribution of high definition television from a satellite dish or cablebox to anywhere in the house. The 802.11a specification is going to be used to do that. (Remember that Wi-Fi currently uses the 802.11b spec.) 802.11a has a wireless bandwidth of between 12 and 54 Mbps. It also works in the 5 GHz band, which is safely away from Bluetooth territory.

While you wait to see how this thriller works itself out, here's some fun homework. Microwave a burrito for lunch sometime soon and try talking on your 2.4 GHz cordless phone while standing close to the oven at the same time. It's an interesting experiment.

Back to Tech to Go page