Lesson 4 - Wireless LANs

   WPANs and Bluetooth

As smart handheld devices have become more common, the IEEE has created a wireless communication standard for personal area networks (PANs) designated as the IEEE 802.15.1ä-2002 specification. The Bluetooth specification essentially promises to replace the wires that currently connect devices such as headphones, computer mice, and keyboards with short-range, low power, 2.4GHz wireless links. Furthermore, the technology is able to provide seamless connectivity between devices that are near each other, even temporarily. For example, a traveler might check e-mail by simply moving a Personal Digital Assistant (PDA) near an airport kiosk that provides Internet access.

Bluetooth defines three power levels: a low power level that covers a short distance such as might be required to connect a keyboard to a PC, a medium power level suitable to connecting devices over a range of up to 10 meters (33 feet), such as within a single room, and a higher power level that can cover a medium range, such as a home or office. A Bluetooth PAN or "piconet" includes one master device, which controls the frequency-hopping pattern for its small area. The master can link to up to seven slave devices at one time. However, each device may be a member of multiple piconets, moving from one to another as a user changes position.

Bluetooth uses frequency hopping spread spectrum radio in the 2.4GHz range. Because 802.11b wireless LANs use the same frequency band, some interference between the technologies does occur, because a Bluetooth PAN will occasionally hop to one of the frequencies being used by the 802.11b LAN. The effect of this interference becomes stronger the closer two interfering devices are to each other. A device that contains both an 802.11b NIC and Bluetooth transceiver could notice poor performance on both sys-tems if they are being used at the same time. For example, if a user listens to a Moving Pictures Experts Group, Layer-3 (MP3) file on Bluetooth headphones, while using the same computer to transfer a file over the wireless LAN, then both operations will suffer.

To resolve this problem, the IEEE 802.15.2 working group is currently developing techniques to reduce interference between Bluetooth devices and 802.11 wireless LANs. Until this specification is finalized, some experts recommend using 5GHz (802.11a) wireless devices where interference in the 2.4GHz range proves problematic.

   Activities

See the Activities and Extended Activities section in Unit 5 Lesson 4 in your textbook Introduction to Networking to test what you have learned so far.

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