Bluetooth(P10U4)
Bluetooth wireless technology is a short
range communications technology intended to replace the cables connecting
portable unit and maintaining high levels of security. Bluetooth technology is
based on Ad-hoc technology also
known as Ad-hoc Pico nets,
which is a local area network with a very limited coverage.
History
of Bluetooth
WLAN technology enables device connectivity
to infrastructure based services through a wireless carrier provider. The need
for personal devices to communicate wirelessly with one another without an
established infrastructure has led to the emergence of Personal Area Networks (PANs).
- Ericsson's Bluetooth project in 1994 defines the standard for
PANs to enable communication between mobile phones using low power and low
cost radio interfaces.
- In May 1988, Companies such as IBM, Intel, Nokia and Toshiba
joined Ericsson to form the Bluetooth Special Interest Group (SIG) whose
aim was to develop a defacto standard for PANs.
- IEEE has approved a Bluetooth based standard named IEEE
802.15.1 for Wireless Personal Area Networks (WPANs). IEEE standard covers
MAC and Physical layer applications.
Bluetooth specification details the entire protocol stack. Bluetooth
employs Radio Frequency (RF) for communication. It makes use of frequency modulation to generate
radio waves in the ISM band.
The
usage of Bluetooth has widely increased for its special features.
- Bluetooth offers a uniform structure for a wide range of
devices to connect and communicate with each other.
- Bluetooth technology has achieved global acceptance such that
any Bluetooth enabled device, almost everywhere in the world, can be
connected with Bluetooth enabled devices.
- Low power consumption of Bluetooth technology and an offered
range of up to ten meters has paved the way for several usage models.
- Bluetooth offers interactive conference by establishing an
adhoc network of laptops.
- Bluetooth usage model includes cordless computer, intercom,
cordless phone and mobile phones.
Piconets
and Scatternets:
Bluetooth enabled electronic devices
connect and communicate wirelessly through shortrange devices known as Piconets. Bluetooth devices exist in
small ad-hoc configurations with the ability to act either as master or slave
the specification allows a mechanism for master and slave to
switch their roles. Point to point configuration with one master and one slave
is the simplest configuration.
When more than two Bluetooth devices
communicate with one another, this is called a PICONET. A Piconet can contain up to seven slaves clustered around
a single master. The device that initializes establishment of the Piconet
becomes the master.
The master is responsible for transmission
control by dividing the network into a series of time slots amongst the network
members, as a part of time
division multiplexing scheme which is shown below.
The
features of Piconets are as follows −
- Within a Piconet, the timing of various devices and the
frequency hopping sequence of individual devices is determined by the
clock and unique 48-bit
address of master.
- Each device can communicate simultaneously with up to seven
other devices within a single Piconet.
- Each device can communicate with several piconets
simultaneously.
- Piconets are established dynamically and automatically as
Bluetooth enabled devices enter and leave piconets.
- There is no direct connection between the slaves and all the
connections are essentially master-to-slave or slave-to-master.
- Slaves are allowed to transmit once these have been polled by
the master.
- Transmission starts in the slave-to-master time slot
immediately following a polling packet from the master.
- A device can be a member of two or more piconets, jumping from
one piconet to another by adjusting the transmission regime-timing and
frequency hopping sequence dictated by the master device of the second
piconet.
- It can be a slave in one piconet and master in another. It
however cannot be a master in more than once piconet.
- Devices resident in adjacent piconets provide a bridge to
support inner-piconet connections, allowing assemblies of linked piconets
to form a physically extensible communication infrastructure known
as Scatternet.
Spectrum:
Bluetooth technology operates in the
unlicensed industrial, scientific and medical (ISM) band at 2.4 to 2.485 GHZ,
using a spread spectrum hopping, full-duplex signal at a nominal rate of 1600
hops/sec. the 2.4 GHZ ISM band is available and unlicensed in most countries.
Range
Bluetooth operating range depends on the
device Class 3 radios have a range of up to 1 meter or 3 feet Class 2 radios
are most commonly found in mobile devices have a range of 10 meters or 30 feet
Class 1 radios are used primarily in industrial use cases have a range of 100
meters or 300 feet.
Data rate
Bluetooth supports 1Mbps data rate for
version 1.2 and 3Mbps data rate for Version 2.0 combined with Error Data Rate.
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