Bluetooth fills the niche of very short-range communication between mobile phones,PDAs, Notebook computers, and other personal or peripheral devices. For example, Bluetooth can be used to connect a mobile phone to a headset, or a notebook computer to a printer. Bluetooth is a more convenient alternative to connecting two devices with a wire. In such applications, it is not necessary to provide much range or bandwidth. This is fortunate for some of the target battery-powered devices, since it is important that they not consume much power.
Bluetooth operates in the license-exempt band at 2.45 GHz. It has a range of only about 10 m. For this reason, and because the communicating devices typically belong to one individual or group, Bluetooth is sometimes categorized as a personal area network (PAN). Version 2.0 provides speeds up to 2.1 Mbps. Power consumption is low.Bluetooth is specified by an industry consortium called the Bluetooth Special Interest Group. It specifies an entire suite of protocols, going beyond the link layer to define application protocols, which it calls profiles, for a range of applications. For example, there is a profile for synchronizing a PDA with a personal computer. Another profile gives a mobile computer access to a wired LAN in the manner of 802.11, although this was not Bluetooth’s original goal.
The IEEE 802.15.1 standard is based on Bluetooth but excludes the application protocols. The basic Bluetooth network configuration, called a piconet, consists of a master device and up to seven slave devices. Any communication is between the master and a slave; the slaves do not communicate directly with each other. Because slaves have a simpler role, their Bluetooth hardware and software can be simpler and cheaper.Since Bluetooth operates in an license-exempt band, it is required to use spread spectrum Technique to deal with possible interference in the band. It uses frequency hopping with 79 channels (frequencies), using each for 625 μm at a time. This provides a natural time slot for Bluetooth to use for synchronous time division multiplexing. A frame takes up 1, 3, or 5 consecutive time slots.
A slave device can be parked: set to an inactive, low-power state. A parked device cannot communicate on the piconet; it can only be reactivated by the master. A piconet can have up to 255 parked devices in addition to its active slave devices. ZigBee is a newer technology that competes with Bluetooth to some extent. Devised by the ZigBee alliance and standardized as IEEE 802.15.4, it is designed for situations where the bandwidth requirements are low and power consumption must be very low to give very long battery life. It is also intended to be simpler and cheaper than Bluetooth, making it financially feasible to incorporate in cheaper devices such as a wall switch that wirelessly communicates with a ceiling-mounted fan.