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Channel Definition
The
channel is represented by a pseudo-random hopping sequence hopping
through the 79 or 23 RF channels.The hopping sequence is unique for
piconet and is determined by the Bluetooth device address of the
master; the phase in the hopping sequence is determined by the
Bluetooth clock of the master.(How
the master determine the hopping sequence and hopping
phase?) The channel is divided into time slots where each
slot correspongds to an RF hop fequency.Consecutive hops correspond
to different RF hop frequencies. The nominal hop rate is
1600 hops/s. All Bluetooth units participating in
the piconet are time- and hop-synchronized to the channel.
Time Slots
The
channel is divided into time slots, each 625 μs in length. The
time slots are numbered according to the bluetooth clock of the
piconet master. The slot numbering ranges from 0 to 2^27-1 and is
cyclic with a cycle length of 2^27.
In the time
slots, master and slave can transmit packets.
A TDD scheme
is used where master and slave alternatively trasmit.
The master shall start its transmission in even-numbered time slots only, and the
slave shall start its transmission in odd-numbered time slots only. The
packet start shall be aligned with the slot start.Packets
transmitted by the master or the slave may extend over up to
five time slots.
The RF hop
frequency shall remain fixed for the duration of the packet.For a
single packet, the RF hop freqency to be used is derived form the
current Bluetooth clock value. For a multi-slot packet, the RF hop
frequency to be used for the entire packet is derived from the
Bluetooth clock value in the first slot of the packet. The RF hop
frequency in the first slot after a multi-slot packet shall use the
frequency as determined by the current Bluetooth clock value.
If a packet occupies more than one time slot, the hop frequency
applied shall be the hop frequency as applied in the time slot
where the packet transimission was started.
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