Bluetooth Technology Explanation
How many electronic devices do you see around you: three, four, five, more? With Bluetooth, you can control them without moving an inch. Just key in a command on your mobile phone or Personal Digital Assistant (PDA) and Bluetooth transmits it. Or plug a Bluetooth USB adapter or "dongle" into your desktop, laptop or netbook computer. Seconds later, your printer, scanner, lap-top, camcorder or microwave springs into action.
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Bluetooth
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A scaled-down version of Wi-Fi, Bluetooth carries one, two or three megabits of data per second depending on its class, it's a low-power, short-range radio link between specially-equipped devices. Broadcasting at 2.4 Gigahertz (GHz)--a very high frequenc--Bluetooth Class 3 nonetheless operates on just 1 milliwatt (mW) of electricity. Class 2 runs on 2.5 mW, older Class 1 on 100 mW. A standard light bulb by comparison requires 60 watts. Batteries last a long time, making Bluetooth very cost-efficient.
Range
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Low power weakens a signal's strength, curtailing it range. But this drawback has its virtues: electronic eavesdroppers rarely pick up its signal. And there are fewer signals from nearby devices to cause interference. The Class 2 and Class 3 Bluetooth devices commonly used today transmit in radii of 50 to 100 feet (15 to 30 meters) and 16 to 33 feet (5 to 10 meters) respectively. Within these confines, though, a Bluetooth transmitter can connect to up to eight devices at one time.
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Frequency Hopping
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Still, bandwidth in the 2.4 GHz range is jam-packed with radio signals. So much so, competing signals drown out Bluetooth ones even at low-power levels. They would end up garbled or lost were it not for a technique called spread-spectrum frequency-hopping. Packets of data are sent 1,600 times a second over one 79 available sub-channels located between 2.400 -- 2.4835 GHz. Whenever possible, a packet is assigned successive sub-channels or slots. Sometimes, though, interference crops up between transmission and reception. Bluetooth compensates for this by rerouting the signal to the next available slot.
Formats
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Bluetooth creates a Piconet (personal area network) between nearby devices, one acting as the "master" polling and transmitting to the other "slaves." Software-driven logical links set up the physical connection between devices. Each of these is assigned its own unique access code by the Bluetooth Special Interest Group positioned at the beginning of every data packet. A "header" carrying logical link information lies adjacent to it. The packet payload comes next in the Basic Rate Bluetooth signal format. In the Enhanced Data version, the guard--a short interval reserved for remodulating the signal--comes after the header followed by a synchronization sequence. Both clear the way for the delivery of the adjoining payload. A brief "trailer" marking the end of the packet is then sent.
History
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Ericcson, a Swedish electronics firm, created Bluetooth in the mid-1990s . Recognizing its potential, Intel, IBM, Nokia and Toshiba spurred the development of an industry-wide transmission format, Standard 1.0, released in 1999. Sales of Bluetooth-enabling chips to mobile phones, PC cards and headset manufacturers began a year later. Printers, laptops and hands-free car-phone-kits had them by 2002, MP3 players and medical equipment by 2003. According to the Bluetooth Special Interest Group, a total of 250 million Bluetooth-enabled devices were in consumers' hands in 2004, the year Standard 2.0 supporting an enhanced data rate was released. In 2006 it was 1 billion, in 2008 it was 2 billion. Developers introduced Standard 3 in 2009.
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