Bluetooth

Bluetooth is the name of a wireless technology for short-range radio communications. Bluetooth is especially intended for the communications between devices, such as mobile telephones, computers and peripheral equipment. Bluetooth eliminates the need for wires.

The communications in Bluetooth is based on an ad-hoc network. This so-called piconet has a master and up to 7 slaves. A device can be part of more than one piconet. In this case the network is extended to a scatternet.

The data rates are not very high. The first generation of Bluetooth had a maximum bit rate of 721 kbps. In the second generation the maximum bit rate is tripled. The transmission is very robust through the use of frequency hopping. Bluetooth uses the globally available 2.4 GHz band.

There are three different power classes in Bluetooth.

• Class 1: maximum output power 100 mW (20 dBm). Used for extended range up to about 100 m;
• Class 2: maximum output power 2,5 mW (4 dBm). Normal usage, range up to about 10 m;
• Class 3: maximum output power 1 mW (0 dBm). Short range communications from 10 cm up to 1 m.

Security of Bluetooth is based on devices. Devices can be either trusted or non trusted. Each device has a unique 48-bit identifaction code. A device can be put in a sensing mode to search for other devices within reach.

The development of Bluetooth is in the hands of the Bluetooth Special Interest Group.

The name comes from an old king of the Vikings, Harald Blaetand who united Denmark and Norway in the latter part of the 10th century.

Bluetooth is standardized under IEEE 802.15.1.