Bluetooth is an industrial standard for wireless personal area networks (PANs). It enables connection and exchange of information between devices such as mobile phones, laptops, printers, and the like. The link is provided under a secure, globally unlicensed shortwave radio frequency. It eliminates the need for user intervention and keeps transmission power to the barest minimum to save on battery power. Now, when two or more devices are to be connected to one another, they agree on several matters before the conversation can begin: For instance, how much data is to be sent between devices? Over what medium is data to be transmitted, wires or through wireless? Which protocol is to be used for communication? Bluetooth provides agreement at the physical level because it uses the radio frequency standard, and provides agreement at the protocol level, where devices agree on the amount of data to be sent, how much data will be sent at a time, and whether the devices in a network can tell whether the message sent is the same as the one that was received.
Bluetooth is attractive because it is wireless and relatively inexpensive. It is also automatic. Other equivalent technologies that use wireless technologies, such as infrared, are available, but one drawback to infrared is that it is a line-of-sight technology. For instance, devices that use the technology, such as remote controls, have to be pointed at the television. Also, it is a one-on-one technology, which means that only two devices can be used at a particular time. Bluetooth, on the other hand, can be used by many devices (up to eight devices) at the same time. For instance, when driving toward your home, you may tell a friend to call you back after a few minutes. Once in the house, you may have the map that was received from your car’s Bluetooth-enabled GPS to be sent to your computer or printer, and when your friend calls you back, the call may be received through your Bluetooth-enabled home phone instead of the cell phone; Bluetooth can detect that you are at home now by picking up the signal from your cell phone.
Transmission of data through Bluetooth is through low-power radio waves between 2.402 and 2.480 GHz. In order not to interfere with other systems or equipments around it, Bluetooth transmits rather weak signals of about 1 mW. Contrast this to powerful cell phones that can transmit about 3 mW. This low-power signal limits the range of Bluetooth devices to about 10 m. Walls in the house do not interfere with a Bluetooth signal. With much equipment using the technology, it is easy to imagine devices interfering with one another. Bluetooth avoids that by using a technology called Spread-Spectrum Frequency Hopping, which reduces the chance of two devices using the same frequency. The frequencies are randomly chosen, and they may change regularly. When Bluetooth devices are within range, a conversation between them occurs to determine whether they have data to share or whether one will control the others. It is an automatic process. Bluetooth devices use a personal area network or Piconet. Once a Piconet is established, the frequencies of the device members hop frequently and simultaneously to keep in touch with one another and to avoid other Piconets that may be in the same room.
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