Bluetooth could interfere with Lans

Users considering the implementation of Bluetooth wireless personal area networks (WPans) into environments containing wireless local area networks (WLans)...

Users considering the implementation of Bluetooth wireless personal area networks (WPans) into environments containing wireless local area networks (WLans) need to beware of potential interference problems with 802.11b.

Bluetooth, potentially one of the most widely-backed, rapidly-adopted standards ever, could cause problems when it is introduced to an office environment where 802.11b is present because they both operate in the unlicenced 2.4-2.48GHz ISM (instrumentation, scientific and medical) frequency range.

Products supporting 802.11b began to ship in 1999 and have made considerable inroads into the enterprise market. Prices for network interface cards and Wlan access points have come down significantly, and have made WLans a viable extension to the wired Lan. Analyst firm Cahners In-Stat estimates the market size in 1999 at $990m (£705m), climbing to $1.3bn (£925m) in 2000 and $1.7bn (£1.2bn) in 2001. Supporting the market, Microsoft recently ann-ounced a specification for Tablet PCs, which favours 802.11b over Bluetooth.

Gemma Paulo, an analyst with Cahners In-Stat, explained the likely shape of the problem. "Employees in offices will bring in their cell phones with Bluetooth installed while trying to work on their WLans. Bluetooth uses frequency hopping spread spectrum [FHSS] technology, while 802.11b uses direct sequence [DSSS]. Frequency hopping transmissions can generally hop around interference but DSSS systems have a harder time overcoming this interference.

"In 2002 and 2003, we expect to have interference problems as Bluetooth devices increasingly enter the Lan environment, where WLans are functioning."

Robin Gear, an analyst with Ovum, counselled caution. "It is not clear which of the standards will win out, though 802.11b is more widely deployed already. The parties to the standards debate are talking to each other. Potential users should wait and see how the situation progresses," he said.

Bluetooth is aimed at smaller devices such as palmtops and peripherals, while 802.11b will operate at the current Lan device level. The problem will occur at the MAC (Media Access Control) level of the network transmission model. This layer contains the addressing of the information being sent between stations.

The 802.11b specification and its rival HomeRF also have a potential interference issue because HomeRF uses FHSS, thus making "hopping" into DSSS frequencies possible. The problem is less likely to occur, though, because the technologies are direct competitors, whereas Bluetooth is complementary to them.

Interference: the basic conflict

  • 802.11b uses a transmission methods in which data is spread out into the full bandwidth of the channel (DSSS) whereas Bluetooth uses FHSS, where the frequency of the signal is changed several times a second. The problem of interference between the two wireless standards is rooted in the possibility of Bluetooth "hopping" into frequencies used by 802.11b and affecting MAC-level addressing information

  • Bluetooth and 802.11b are complementary technologies - Bluetooth as a wireless personal area network standard for peripherals and 802.11b for Lan-level devices

    Solving the problem

    For users, three possible solutions are suggested:

  • Wait for 5GHz technology to mature. However, analysts point out this will not be able to be compressed into a PC card for 2-3 years

  • Wait a year for Mobilian's Trueradio solution which explicitly addresses WLan and WPan interoperability

  • Wait for modified MAC software so 802.11b network access points are able to differentiate Bluetooth traffic from 802.11b traffic, effectively shutting down when Bluetooth traffic comes in range of the 802.11b access point.

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