Saturday, February 5, 2011

BLUETOOTH

Bluetooth is a wireless LAN technology designed to connect devices of different functions such as telephones, notebooks, computers (desktop and laptop), cameras, printers, coffee makers, and so on. A Bluetooth LAN is an ad hoc network, which means that the network is formed spontaneously; the devices, sometimes called gadgets, find each other and make a network called a piconet. A Bluetooth LAN can even be connected to the Internet if one of the gadgets has this capability. A Bluetooth LAN, by nature, can not be large. If there are many gadgets that try to connect, there is chaos. Bluetooth technology has several applications. Peripheral devices such as a wireless mouse or keyboard can communicate with the computer through this technology. Monitoring devices can communicate with sensor devices in a small health care center. Home security devices can use this technology to connect different sensors to the main security controller. Conference attendees can synchronize their laptop computers at a conference. Bluetooth was originally started as a project by the Ericsson Company. It is named for Harald Blaatand the king of Denmark (940-981) who united Denmark and Norway.

Blaatand translates to Bluetooth in English. :

Today, Bluetooth technology is the implementation of a protocol defined by the
IEEE 802.15 standard. The standard defines a wireless personal-area network (PAN)
operable in an area the size of a room or a hall.

Architecture :

Bluetooth defines two types of networks: piconet and scatternet.

Piconets :

A Bluetooth network is called a piconet, or a small net. A piconet can have up to eight stations, one of which is called the primary; ? the rest are called secondaries. All the secondary stations synchronize their clocks and hopping sequence with the primary.Note that a piconet can have only one primary station. The communication between the primary and the secondary can be one-to-one or one-to-many.

Although a piconet can have a maximum of seven secondaries, an additional eight secondaries can be in the parked state. A secondary in a parked state is synchronize with the primary, but cannot take part in communication until it is moved from the parked state. Because only eight stations can be active in a piconet, activating a station from the parked state means that an active station must go to the parked state.

Scatternet :

Piconets can be combined to form what is called a scatternet. A secondary station intone piconet can be the primary in another piconet. This station can receive messages from the primary in the first piconet (as a secondary) and, acting as a primary, deliver them to secondaries in the second piconet. A station can be a member of two piconets.

Bluetooth Devices :
A Bluetooth device has a built-in short-range radio transmitter. The current data rate is 1 Mbps with a 2.4-GHz bandwidth. This means that there is a possibility of interference between the IEEE 802.1 lb wireless LANs and Bluetooth LANs.

Radio Layer :

The radio layer is roughly equivalent to the physical layer of the Internet model. Bluetooth devices are low-power and have a range of 10 m.

Band :

Bluetooth uses a 2.4-GHz ISM band divided into 79 channels of 1 MHz each.

FHSS:
Bluetooth uses the frequency-hopping spread spectrum (FHSS) method in the physical layer to avoid interference from other devices or other networks. Bluetooth hops 1600 times per second, which means that each device changes its modulation frequency 1600 times per second. A device uses a frequency for only 625 gs (1/1600 s) before it hops to another frequency; the dwell time is 625 gs.

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