Introduction
Bluetooth, the new technology named after the 10th Century Danish King Harold Bluetooth, is a hot topic among wireless developers. This article will provide an introduction to the technology.
Bluetooth was designed to allow low bandwidth wireless connections to become so simple to use that they seamlessly integrate into your daily life. A simple example of a Bluetooth application is updating the phone directory of your mobile phone. Today, you would have to either manually enter the names and phone numbers of all your contacts or use a cable or IR link between your phone and your PC and start an application to synchronize the contact information.
Bluetooth Specification
Technical features:
Bluetooth operates in the unlicensed 2.4 GHz Industrial Scientific Medical (ISM) frequency band as shown in Figure 4 below. It uses 79 channels between 2.402 GHz to 2.480 GHz (Brent, Bisdikian, 2002, p. 17). It uses power of 1mW to 100mW. The nominal range is 10 meters, but can be extended to more than 100 meters by increasing the transmission power to 100mW. The gross data rate is 1Mbps (Bray, Sturman, 2002, p. 8). Bluetooth uses a combination of packet and circuit switching technologies for transmission.
Access Technology
Since Bluetooth operates in the unlicensed ISM band that is also used by other devices such as 802.11 networks, baby monitors, garage door openers, microwave ovens etc, there is possibility of interference (Helsinki University of Technology, 2000). To avoid interference,
Bluetooth uses an access technology called Frequency Hop Spread Spectrum (FHSS). The band where Bluetooth operates is divided into 79 channels of 1 MHz each (Bray, Sturman, 2002, p. 8).
Each channel is divided into time slots consisting of 625 µsec in length. After a packet is sent on one frequency, both the devices retune their radios to a different frequency, effectively hopping at a rate of 1600 hops per second through different time slots (Brent, Bisdikian, 2002, p. 94)..................
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