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Wireless Basics

Bluetooth



Technology Summary

Bluetooth is not really intended to be a wireless LAN (WLAN) technology, but aimed at providing nearly automatic connectivity among small groups of devices without a formal network infrastructure. Think of it as something that could wirelessly enable your PDA to print to a nearby printer, or your connect your cell phone to a headset. Bluetooth's primary advantages over wireless LAN technologies are its lower power consumption and easy set up (at least in theory). Its weaknesses are that it can be a bit too promiscuous in allowing connectivity and its low data rate - 721 kbps normally, but up to 2.1Mbps for Bluetooth 2.0's Enhanced Data Rate (EDR).

Bluetooth uses Frequency-Hopping Spread-Spectrum (FHSS) and operates in the same 2.4GHz band as 802.11b/g devices. FHSS is a spread spectrum modulation scheme that uses a narrowband carrier that changes frequency in a pattern known to both transmitter and receiver. So 802.11b/g devices can't understand Bluetooth transmissions, which appear as yet another noise source. There can be an unlimited number of devices in a Bluetooth network (called a "piconet"). But only eight (1 master plus 7 slaves) can be active at a time.

This technology has had a rough birthing process, but seems to finally found its groove for getting rid of wires for keyboards, mice and headsets. (The wireless Bluetooth headset market actually has three segments: consumer audio, mobile phone/PDA, and computer, each with different physical designs.) But all of Bluetooth's problems are not behind it. Windows support - even in XP2 - remains a mess and user interfaces are still evolving.

One of the key troublemakers is the large number of profiles that Bluetooth devices can (or more often cannot) support. Just finding an up-to-date list of the profiles is a real job. Here's the one on wikipedia, which looks to be relatively up to date. This Bluetooth Profile dependency diagram on palowireless is also helpful in sorting out the relationships among the profiles. Although some profiles may not make sense for certain devices, you'd better hope the general-purpose Bluetooth adapter that you purchase for your desktop or notebook supports them all - or at least the profiles required by the device that you want to connect to!


Enhanced versions

There aren't really any non-standard enhancements to Bluetooth, although there are five versions of the standard - 1.0, 1.0B, 1.1, 1.2 and 2.0 - and three Classes (or power levels). Most devlces you'll find are either Class 1 (100 mW) or Class 2 (2.5 mW), with Class 3 (1 mW) devices mainly found in SD card form or embedded into devices.

Note that some manufacturers have also developed proprietary profiles.

Positives

  • Simple peer-to-peer low-speed wireless networking
  • Low power consumption

Negatives

  • Not all adapters support all profiles
  • Default settings can be a security risk
  • Can cause interference with 802.11b/g WLANs

Recommendation: Not useful to construct a WLAN, but very handy for getting rid of wires, especially in mobile and VoIP applications.

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