Image Processing Reference
In-Depth Information
( µs-) time slot only, but they are differentiated by their payload FEC. The packet payloads are
either unprotected (called HV) or / rate FEC-encoded (HV) or protected with a /-rate repeti-
tion code (HV). For an HV connection, a packet is transmitted every sixth slot (see Figure .),
for HV every fourth slot, and for HV every second slot (meaning that with one HV connection
no other traffic can be transmitted in the piconet). Up to the Bluetooth Specification . [Blu]
there was no ARQ-scheme for SCO-links. In case of an erroneous reception of the packet over-
head, the SCO-packet was replaced by an erasure pattern. In case noncorrectable bit errors occurred
in the payload only, these errors were forwarded to the speech decoder. The Bluetooth Specifica-
tion . [Blu] includes an “enhanced” SCO-link. his link allows a very flexible deployment of the
SCO-link, providing for a reserved bandwidth for several transmission rates and a limited number
of retransmissions.
To further improve coexistence with other systems in the ISM-band, Bluetooth Version .
includes the possibility to perform adaptive FH (AFH), i.e., to exclude interfered carriers from
thehopsequence.WithAFHthenominalhopratewillbehalved,becausethespeciicationhas
been changed such that the slave responds on the same frequency as on which it received the
packet from the master [Blu]. he Bluetooth specification supports security by authentication and
encryption.
Available publications on Bluetooth's radio network performance and its suitability for industrial
environments generally use the Bluetooth .x versions as a basis. Nevertheless, later Bluetooth spec-
ifications exist. Bluetooth .
EDR (Enhanced Data Rate) allows for double or triple transmission
rates by modulating more bits into one symbol, i.e., by using a π/DQPSK (. kbps) or an DPSK
(. kbps) instead of the GFSK. he standard is backward compatible and decides on the modula-
tion scheme depending on the availability and link quality. Bluetooth . + EDR (published in August
) enables, among others, “Secure Simple Pairing” (which deploys, if available, near field commu-
nication technology) and an extended sleep mode for improved power saving. Latest standardization
activities foresee a high speed channel, whose physical layer is based on ultra wide band and whose
MAC is based on the WiMedia MAC. A transmission in the - GHz domain is discussed as well as
transmission rates up to Mbps.
+
25.3.2 Performance
On the factory floor, Bluetooth can be used as a wireless add-on to wired systems or as a replacement
of existing cabling. It can cover machine-to-machine communication, wireless/remote monitoring,
or tracking and some type of positioning of moving entities [GGH,Bea]. [BW] and [Rug]
investigate the performance of a single Bluetooth link in a factory environment. The bit error rate
(BER) turned out to be somewhat worse there than in an office environment. Nevertheless, the
technologywasseenassuitablefortheusecase.
Considering the comparably short range of Bluetooth and the likely association to a specific unit
(represented by a machine/person/task), it is furthermore possible that several independently active
Bluetooth piconets coexist and overlap in space. he use of FH helps to mitigate the effects of inter-
ference among these piconets. When assuming more or less time synchronized piconets, a worst-case
approximation of the loss rate can be made with Equation .. It calculates the probability
P
(
x
,
n
)
that of
x
other piconets
n
hop onto the same frequency as the considered piconet:
n
x
−
n
x
n
)(
)
)
P
(
x
,
n
)=(
(
.
(.)
The probability that at least one of the other
x
piconets transmits on the same frequency is then
P
(
x
)=
−
P
(
x
,
)
. The smaller the number of interfering piconets, the better the approximation
