原创 Whatisbluetooth

    Bluetooth is
a short-range radio link intended to replace the cable(s)
connecting portable and/or fixed electronic devices. Key feathers
are robustness, low complexity, low power, and low cost.

    Bluetooth
operates in the unliscensed ISM band at 2.4 GHz. A frequency hop
transceiver is applied to combat interference and fading. A shaped,
binary FM modulation is applied to minimize transceiver complexity.
The symbol rate is 1 Ms/s. A slotted channel is applied with a
nominal slot length of 625 μs. For full duplex transmission, a
Time-Division Duplex(TDD) scheme is used. Onthe channel,
information is exchanged thrugh packets. Each packet is transmitted
on a different hop frequency. A packet nominally covers a single
slot, but can be extended to cover up to five slots.

    The
bluetooth protocol uses a combination of circuit and packet
switching. Slots can be reserved for synchronous packets.
Bluetooth can support an asynchronous data channel, up to three
simultaneous synchronous voice channels,or a channel which
simultaneously supports  synchronous data and
synchronous voice. Each voice channel supports 64 kb/s synchronous(voice) channel in
each directin. The asynchronous channel can support maximal
723.2 kb/s asymmetric(and sill up to
57.6kb/s in the return
direction), or 433.9 kb/s
symmetric.(What are the differences between asymmetric
and symmetric?)

    The
bluetooth system consists of a radio unit, a link control unit, and
a support unit for link management and host terminal interface
functions.

    The
bluetooth system provides a point-to-point connectin (only two
bluetooth units involved), or a point to multipoint connection. In
the point-to-multipoint connectin, the channel is shared among
several bluetooth units. Two or more units sharing the same channel
from a piconet. Bluetooth unit acts as the master of the piconet,
whereas the other unit(s) acts as slave(s). Up to seven slaves can
be active in the piconet. In addition, many more slaves can remain
locked to the master in a so-called parked state. These parked
slaves cannot be active on the channel, but remain synchronized to
the master. Both for  active and parked slaves,
the channel access is controlled by the master.(How to activate the
parked slaves?)

    Multiple
piconets with overlapping coverage areas from a scatternet.Each piconet can only have a
single master. However, slaves can participate in different
piconets on a time-division multiplex basis. In addtion, a master
in one piconet can be a slave in another piconet. THe piconets
shall not be frequency-synchronized. Each piconet has its own
hopping channel.