Image Processing Reference
In-Depth Information
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HV3
DH1
HV3
DH1
HV3
Master
POLL
DH3
HV3
HV3
Slave 1
HV3
Slave 2
DH
DH
DH3
Slave 3
ACK
FIGURE .
Exampleslotoccupationwithinonepiconetconsistingofmasterandthreeslaves;toslavethereis
anSCO-link,toslave(best-efort)traicistransmittedinbothdirections,slavehascurrentlynothingtosend(but
has to respond to the POLL-packet with an ACK); during the transmission of multislot packets the frequency is not
changed. (From Matheus, K.
Industrial Information Technology Handbook
.Ed.R.Zurawski,CRCPress,BocaRaton,
FL, . With permission.)
every unit has to listen only during the first µs of its receive slot whether there is a packet arriving
(and if not, can “close down” until the next receive slot
∗
).hismeansitneedstolistenintothechannel
only µs
.% of the time, during an active connection in which no packets are
sent. Yet another facet to the long battery life is the low basic transmit power of dBm (resulting
in a nominal range of about m). Bluetooth can also be used with up to dBm transmit power.
This results in a larger range but requires the implementation of power control to fulfill the FCC
sharing rules.
Bluetooth provides two in principle different types of connections: ACL (asynchronous
connection-less) links foreseen for data transmission and SCO (synchronous connection oriented)
links foreseen for speech transmission.
For ACL-links there are six packet types defined. The packets occupy either one, three, or five
( µs-) time slots and their payloads are either uncoded (called DH, DH, DH) or protected with
a /-rate FEC using a (,) shortened Hamming block code without any interleaving (called DM,
DM, DM). An automatic repeat request (ARQ) scheme initiates the retransmission of a packet in
case the evaluation of the cyclic redundancy check included in each ACL-payload shows inconsisten-
cies. his secures error-free reception of the transmitted information. Table . gives an overview on
the throughput values achievable with ACL-connections. he maximum (unidirectional) Bluetooth
throughput is kbps.
As speech transmission is delay sensitive, the original SCO-links support three different packet
types that are transmitted at fixed intervals. These types were designed to transport CVSD (con-
tinuous variable slope delta) encoded speech at kbps. The packet types occupy always just one
/(
×
µs
)=
TABLE .
Throughput Values for ACL-Connections
Unidirectional Throughput Bidirectional Throughput
Name No. of Slots FEC? Max. No. of User Bytes Forward Reverse Forward Reverse
DH no .k .k .k .k
DH no .k .k .k .k
DH no .k .k .k .k
DM / .k .k .k .k
DM / .k .k .k .k
DM / .k .k .k .k
Note:
The reverse link in the unidirectional case transmits DH or DM packets, depending on whether the forward
link uses a DH or DM packet type.
∗
∗This is quite different from channel access schemes like CSMA as used in IEEE . (see Section .). Unless asleep,
IEEE . always has to listen into the channel.
