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Bluetooth is essentially a
protocol for wireless connectivity of diverse set of devices ranging from PDA,
mobile phones, laptops to cooking
oven, fridge, thermostat etc. in home-like environment. An environment
where each device in your home is connected to each other, where devices
think and care about themselves, where they think and care about you; who
identify "you" as an individual different from your spouse and
children. A connectivity which makes your note-pad or cell-phone as your
identity in a crowded room or air-port lounge.
Bluetooth SIG
Bluetooth came out of the womb of Ericsson
somewhere around late 90's and is currently led by the Promoter Group of
Bluetooth SIG comprising of Ericsson,
Nokia, IBM,
Toshiba, Intel,
3Com, Motorola,
Lucent Technologies and Microsoft.
Currently Bluetooth SIG has more than 1400 members and is one of the
fastest growing SIG. This is the first big effort by all the major
companies of the world to come out with a global standard for wireless
connectivity in home-like environment after previous mess of first and
second generation in cellular communication.
The piconet kingdom
The name
of Bluetooth comes from a Danish ruler "Harald Bluetooth" in
late 900 A.D. who ruled greater part of Denmark and Norway during his
reign. More than the yesterday's Bluetooth, today's Bluetooth is all set
to reign the greater part of our home - from Japan to Europe to America.
More ..
The Bluetooth system has both the point-to-point connection or a
point-to-multipoint connection. In point-to-multipoint connection, the
channel is shared among several bluetooth units. Two or more units sharing
the same channel form a piconet. There is one master unit and upto
seven active slave units in a piconet. These devices can be in either of
the states: active, park, hold and sniff. Multiple piconets with
overlapping coverage areas form a scatternet.
A Bluetooth Piconet
(B: Bluetooth link, S: Slave, M: Master)
The Bluetooth system consists of a radio unit, a link control unit and
a support unit for link management and host terminal interface functions. Bluetooth
radio operates in the 2.4 GHz ISM (Industry, Science and Medicine)
band. The range of Bluetooth radio is anywhere from 10 m. (home) to 100 m.
(Airport lounge) depending on the power of the transmitter at the antenna.
Depending on the class of the device, a bluetooth radio can transmit upto
100 mW (20 dBm) to minimum of 1 mW (0 dBm) of power. It uses frequency
hopping for low interference and fading, uses TDD (Time-Division Duplex)
scheme for full duplex transmission and transmits using GFSK (Gaussian
Frequency Shift Keying) modulation.
Bluetooth protocol uses a combination of circuit and packet switching.
The channel is slotted and slots can be reserved for synchronous packets. Bluetooth
protocol stack can support an asynchronous connection-less (ACL) link
for data and upto three simultaneous synchronous connection-oriented (SCO)
links for voice or a combination of asynchronous data and synchronous voice
(DV packet type). Each voice channel supports a 64 Kb/s synchronous channel
in each direction. The asynchronous channel can support maximum of 723.2
Kb/s uplink and 57.6 Kb/s downlink (or vice versa) or 433.9 Kb/s symmetric
links. The stack primarily has a baseband for physical layer and link
manager and controller for link layer. The upper layer interface depends on
how these two layers are implemented and used with applications. The stack
is shown below.
Bluetooth Stack
More ..
The stack primarily contains a physical level protocol
(Baseband) and a link level protocol (LMP) with an adaptation layer (L2CAP)
for upper layer protocols to interact with lower bluetooth stack.
From here to Radio
With this Bluetooth overview, we move to the next section which talks
about the electrical and physical characteristics of Bluetooth
radio...
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