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Analysis: Interference issues hinder Bluetooth

(IDG) -- Bluetooth is one of those technologies that people call "long-awaited." The wireless local networking scheme just hasn't come online as soon as many people had hoped. One hindrance to Bluetooth's rapid commercialization is the fact that like other technologies, long-awaited or not, there are bugs to work out.

Since Bluetooth does away with cables and works in the RF domain, it may have a few more bugs, especially in the form of incompatibility and interference, than some other technologies. And even if those bugs are eliminated, an error-free Bluetooth network may present problems as well. This is because Bluetooth works in the 2.4-GHz range of the radio band, which is not licensed by the FCC and is inhabited by cell phones, baby monitors and the IEEE 802.11 LAN. INFOCENTER
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Corporate IT managers with existing or planned RF nets will need to become aware of Bluetooth if it gains the ubiquity that some analysts forecast. Almost 2,000 assorted companies have joined an industry group promoting Bluetooth.

Wireless networking consultant and columnist Jim Geier pointed out that a wireless LAN node (like Bluetooth or 802.11) that works on a principle of carrier sensing will not transmit when it senses other stations transmitting. If placed in close proximity to 802.11-based wireless LANs, Bluetooth could cause interference, Geier said. Modern LANs keep working despite such interference, but performance can suffer. Much design effort in Bluetooth -- including limits on physical range and use of spread-spectrum frequency hopping -- went toward avoiding conflict with other transmission schemes.

I spoke recently with Geier about how to handle the potential Bluetooth menace. He said reducing the distances between 802.11 radios and access points may be a useful tactic for handling Bluetooth problems. "Administrators can mediate the problem by making sure there's enough overlap in [wireless] access points for 802.11," he said. As much as 75 percent access node overlap may be required, according to Geier.

"Generally, it's Bluetooth that is interfering with the existing LANs, and not the other way around," said Geier, who explained that Bluetooth hops through different frequencies much faster than 802.11.

Other approaches to Bluetooth and 802.11 LAN integration may require developers to use direct-sequence, instead of frequency-hopping, 802.11 LAN radio cards and access points. Alternatively, Bluetooth device use within 50 feet of 802.11 network points could be barred, said Geier.

Geier noted that an upcoming version of 802.11 (that is, 802.11b) ups the gigahertz range for LAN transmission into the 5-GHz part of the radio spectrum. That will certainly get it out of Bluetooth's way, although, as Geier pointed out, users will continue to buy 802.11(a) LANs, and will support existing 802.11(a) LANs for some time. Descriptions of best practices for cohabiting 802.11 and Bluetooth LANs are expected from an IEEE working group later this year.

Useful templates for integrating multiple wireless LANs could be in order. Bluetooth could come into the enterprise via hot gadgets that workers read about in the press, bring into the office, and set up on their own. Now that many early compatibility issues have been sorted out, the number of Bluetooth-produced releases could grow dramatically.

The menu for Bluetooth-hungry technophiles is growing. Just last week, Sony unveiled the Infostick at the Consumer Electronics Show (CES) in Las Vegas. It is an expansion module that brings wireless Bluetooth capabilities to any device that supports Sony's MemoryStick. Meanwhile, Plantronics previewed a Bluetooth headset at CES 2001, and i2Go released Bluetooth-ready digital audio players and pocket PC devices.

The real bump in Bluetooth adoption is expected in several years, when cost-effective Bluetooth-savvy cellular phones and PDA devices become available. As network and IT managers know, both of those product types can easily be described as ubiquitous.

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