Bluetooth Technology

Bluetooth uses a radio technology referred to as frequency-hopping unfold spectrum, that chops up the info being sent and transmits chunks of it on up to seventy nine bands (1 MHz each; focused from a pair of402 to 2480 MHz) within the vary 2,400-2,483.5 MHz (allowing for guard bands). This vary is within the globally unlicensed Industrial, Scientific and Medical (ISM) a pair of.4 GHz short-range radio frequency band.
Originally Gaussian frequency-shift keying (GFSK) modulation was the sole modulation theme available; subsequently, since the introduction of Bluetooth a pair of.0+EDR, π/4-DQPSK and 8DPSK modulation can also be used between compatible devices. Devices functioning with GFSK are said to be operating in basic rate (BR) mode where a direct information rate of one Mbit/s is feasible. The term Enhanced information Rate (EDR) is employed to explain π/4-DPSK and 8DPSK schemes, every giving a pair of and three Mbit/s respectively. the mixture of those (BR and EDR) modes in Bluetooth radio technology is classed as a "BR/EDR radio".
Bluetooth may be a packet-based protocol with a master-slave structure. One master could communicate with up to seven slaves in an exceedingly piconet; all devices share the master's clock. Packet exchange is predicated on the essential clock, outlined by the master, that ticks at 312.5 µs intervals. 2 clock ticks structure a slot of 625 µs; 2 slots structure a slot try of 1250 µs. within the easy case of single-slot packets the master transmits in even slots and receives in odd slots; the slave, conversely, receives in even slots and transmits in odd slots. Packets could also be one, three or five slots long however in all cases the master transmit can begin in even slots and also the slave transmit in odd slots.
Bluetooth provides a secure thanks to connect and exchange info between devices like faxes, mobile phones, telephones, laptops, personal computers, printers, international Positioning System (GPS) receivers, digital cameras, and video game consoles.

Communication and association
A master Bluetooth device will communicate with a most of seven devices in an exceedingly piconet (an ad-hoc pc network using Bluetooth technology), though not all devices support this limit. The devices will switch roles, by agreement, and also the slave will become the master (for example, a headset initiating a association to a phone can essentially begin as master, as initiator of the connection; however could subsequently opt to be slave).
The Bluetooth Core Specification provides for the association of 2 or a lot of piconets to make a scatternet, within which sure devices simultaneously play the master role in one piconet and also the slave role in another.
At any given time, information will be transferred between the master and one different device (except for the little-used broadcast mode). The master chooses that slave device to address; generally, it switches rapidly from one device to a different in an exceedingly round-robin fashion. Since it's the master that chooses that slave to handle, whereas a slave is (in theory) presupposed to listen in every receive slot, being a master may be a lighter burden than being a slave. Being a master of seven slaves is possible; being a slave of over one master is troublesome. The specification is obscure on needed behaviour in scatternets.
Many USB Bluetooth adapters or "dongles" are obtainable, a number of that additionally embrace an IrDA adapter. Older (pre-2003) Bluetooth dongles, however, have restricted capabilities, giving solely the Bluetooth Enumerator and a less-powerful Bluetooth Radio incarnation. Such devices will link computers with Bluetooth with a distance of one hundred meters, however they are doing not provide as several services as trendy adapters do.