How does Bluetooth work?

Definition
A Bluetooth technology is a high speed low powered wireless technology link that is designed to connect phones or other portable equipment together. It is a specification (IEEE 802.15.1) for the use of low power radio communications to link phones, computers and other network devices over short distance without wires. Wireless signals transmitted with Bluetooth cover short distances, typically up to 30 feet (10 meters).
It is achieved by embedded low cost transceivers into the devices. It supports on the frequency band of 2.45GHz and can support upto 721KBps along with three voice channels. This frequency band has been set aside by international agreement for the use of industrial, scientific and medical devices (ISM).rd-compatible with 1.0 devices.
Bluetooth can connect up to “eight devices” simultaneously and each device offers a unique 48 bit address from the IEEE 802 standard with the connections being made point to point or multipoint.
History Of Bluetooth:
Bluetooth wireless technology was named after a Danish Viking and King, Harald  Blatand; his last name means “Bluetooth” in English. He is credited with uniting Denmark and Norway, just as Bluetooth wireless technology is credited with uniting two disparate devices.
The Bluetooth technology emerged from the task undertaken by Ericsson Mobile Communications in 1994 to find alternative to the use of cables for communication between mobile phones and other devices. In 1998, the companies Ericsson, IBM, Nokia and Toshiba formed the Bluetooth Special Interest Group (SIG) which published the 1st version in 1999.
The first version was 1.2 standard with a data rate speed of 1Mbps. The second version was 2.0+EDR with a data rate speed of 3Mbps. The third was 3.0+HS with speed of 24 Mbps. The latest version is 4.0.
How Bluetooth Works:
Bluetooth Network consists of a Personal Area Network or a piconet which contains a minimum of 2 to maximum of 8 bluetooth peer devices- Usually a single master and upto 7 slaves. A master is the device which initiates communication with other devices. The master device governs the communications link and traffic between itself and the slave devices associated with it. A slave device is the device that responds to the master device. Slave devices are required to synchronize their transmit/receive timing with that of the masters. In addition, transmissions by slave devices are governed by the master device (i.e., the master device dictates when a slave device may transmit). Specifically, a slave may only begin its transmissions in a time slot immediately following the time slot in which it was addressed by the master, or in a time slot explicitly reserved for use by the slave device.

Bluetooth

The frequency hopping sequence is defined by the Bluetooth device address (BD_ADDR) of the master device.  The master device first sends a radio signal asking for response from the particular slave devices within the range of addresses. The slaves respond and synchronize their hop frequency as well as clock with that of the master device.
Scatternets are created when a device becomes an active member of more than one piconet. Essentially, the adjoining device shares its time slots among the different piconets.
 Bluetooth Specifications:
  • Core Specifications : It  defines the Bluetooth protocol stack and the requirements for testing and qualification of Bluetooth-based products.
  • The profiles specification:  It defines usage models that provide detailed information about how to use the Bluetooth protocol for various types of applications.
 The core specification consists of 5 layers:
  • Radio: Radio specifies the requirements for radio transmission – including frequency, modulation, and power characteristics – for a Bluetooth transceiver.
  • Baseband Layer: It defines physical and logical channels and link types (voice or data); specifies various packet formats, transmit and receive timing, channel control, and the mechanism for frequency hopping (hop selection) and device addressing.It specifies point to point or point to multipoint links. The length of a packet can range from 68 bits (shortened access code) to a maximum of 3071 bits.
  • LMP- Link Manager Protocol (LMP): defines the procedures for link set up and ongoing link management.
  • Logical Link Control and Adaptation Protocol (L2CAP): is responsible for adapting upper-layer protocols to the baseband layer.
  •  Service Discovery Protocol (SDP): – allows a Bluetooth device to query other Bluetooth devices for device information, services provided, and the characteristics of those services.
The 1st three layers comprise the Bluetooth module whereas the last two layers make up the host. The interfacing between these two logical groups is called Host Controller Interface.
Advantages of Bluetooth Technology:
  • It removes the problem of radio interference by using a technique called Speed Frequency Hopping.  This technique utilizes 79 channels of particular frequency band, with each device accessing the channel for only 625 microseconds, i.e. the device must toggle between transmitting and receiving data from one time slot to another. This implies the transmitters change frequencies 1,600 times every second, meaning that more devices can make full use of a limited slice of the radio spectrum. This ensures that the interference won’t take place as each transmitter will be on different frequencies.
  • The power consumption of the chip (consisting of transceiver) is low, at about 0.3mW, which makes it possible for least utilization of battery life.
  • It guarantees security at bit level. The authentication is controlled using a 128bit key.
  • It is possible to use Bluetooth for both transferring of data and verbal communication as Bluetooth can support data channels of up to 3 similar voice channels.
  • It overcomes the constraints of line of sight and one to one communication as in other mode of wireless communications like infrared.
Bluetooth Applications:
Cordless Desktop: All (or most) of the peripheral devices (e.g., mouse, keyboard, printer, speakers, etc.) are connected to the PC cordlessly.
Bluetooth Applic

Ultimate headset: It can be used to allow one headset to be used with myriad devices, including telephones, portable computers, stereos, etc.
Bluetooth Application

Automatic synchronization: This usage model makes use of the hidden computing paradigm, which focuses on applications in which devices automatically carry out certain tasks on behalf of the user without user intervention or awareness.

Multimedia Transfer:- Exchanging of multimedia data like songs, videos, pictures can be transferred among devices using Bluetooth.

Bluetooth specification

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