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How Bluetooth Works

How Bluetooth Operates

Bluetooth networking transmits data via low-power radio waves. It communicates on a frequency of 2.45 gigahertz (actually between 2.400 GHz and 2.483.5 GHz, to be exact) [source: Bluetooth SIG]. This frequency band is one of a handful of frequencies that has been set aside by international agreement for the use of industrial, scientific and medical devices (ISM).

A number of devices that you may already use take advantage of this same radio-frequency band. Baby monitors, garage-door openers and the newest generation of cordless phones all make use of frequencies in the ISM band. Making sure that Bluetooth and these other devices don't interfere with one another has been a crucial part of the design process.

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Although the Bluetooth Special Interest Group says the technology can be used at a range of more than 3,281 feet (1 kilometer), one of the ways Bluetooth devices avoid interfering with other systems is by sending out very weak signals of about 100 milliwatts [source: PCMag Encyclopedia]. Using low power limits the range of a Bluetooth device to about 656.2 feet (200 meters), cutting the chances of interference between your computer system and your portable telephone or television [source: PCMag Encyclopedia]. Even with the low power, Bluetooth doesn't require line of sight between communicating devices. The walls in your house won't stop a Bluetooth signal, making the standard useful for controlling several devices in different rooms.

Bluetooth can handle many devices simultaneously. With all those devices in the same 32-foot (10-meter) radius, you might think they'd interfere with one another, but it's unlikely. Bluetooth uses a technique called spread-spectrum frequency hopping that makes it rare for more than one device to be transmitting on the same frequency at the same time. In this technique, a device will use 79 individual, randomly chosen frequencies within a designated range, changing from one to another on a regular basis [source: PC Mag Encyclopedia].

In the case of Bluetooth, the transmitters change frequencies 1,600 times every second, meaning that more devices can make full use of a limited slice of the radio spectrum. Since every Bluetooth transmitter uses spread-spectrum transmitting automatically, it's unlikely that two transmitters will be on the same frequency at the same time. This same technique minimizes the risk that portable phones or baby monitors will disrupt Bluetooth devices, since any interference on a particular frequency will last only a tiny fraction of a second.

When Bluetooth-capable devices come within range of one another, an electronic conversation takes place to determine whether they have data to share or whether one needs to control the other. The user doesn't have to press a button or give a command — the electronic conversation happens automatically. Once the conversation has occurred, the devices — whether they're part of a computer system or a stereo — form a network.

Bluetooth systems create a personal-area network (PAN), or piconet, that may fill a room or may encompass a distance no more than that between a cell phone on a belt-clip and the headset on your head. Once a piconet is established, the members randomly hop frequencies in unison so they stay in touch with one another and avoid other piconets that may be operating in the same room. Let's check out an example of a Bluetooth-connected system.

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