Image Processing Reference
In-Depth Information
23.3.6.2 Bluetooth
Bluetooth was originally designed as a wireless replacement for cellular phone headsets; however,
its mid-range wireless capabilities in terms of distance and power consumption, combined with its
frequency hopping capability for improved noise immunity, have led to its consideration as a wire-
less solution for lower-level connectivity on the manufacturing floor. Bluetooth operates in the same
. GHz frequency band as .b and g, and defines a full OSI communications stack, with the
lower levels published as IEEE standard .. []. Advantages of Bluetooth which make it ideal
for manufacturing include dynamic connection establishment without need for human interaction,
utilization of forward error correction (FEC) for delivering the messages without error and with-
out requiring retransmission, and a frequency hopping capability for improved noise immunity and
coexistence that includes a capability to “learn” of and avoid areas in the spectrum that are crowded
with other transmissions. Drawbacks include loss of efficiency from the FEC capability (a  Mbps
communications channel can deliver only  Kbps), and disruption of . transmissions (coex-
istence issue) due to the fact that the technology frequency hops at a faster rate than specified for
.b/g [,].
Bluetooth applications have also been shown to exhibit nondeterministic response time behavior
in the face of ambient interference. While this behavior is not limited to Bluetooth wireless systems,
it provides a good example of an issue that must be addressed before common wireless technologies
can be utilized effectively in NCSs. As an example, Figure . shows the results of an experiment to
better understand the determinism of a Bluetooth NCS. As shown in Figure .a, the test setup
includes two Bluetooth nodes, namely, a controller and an I/O block, and a DeviceNet network
DeviceNet
network
PLC
Device Net
Network
PLC
Bluetooth
Bluetooth
I/O
Bluetooth
Bluetooth
I/O
Packet
sniffer
Packet
Sniffer
(a)
400
350
300
250
200
150
100
50
0
(b)
Number of DN packets before a COS is seen
FIGURE . Experimental characterization of determinism in a Bluetooth system. (a) Bluetooth determinism
performance experimental setup, (b) baseline result with minimal channel noise and near ideal distance between nodes,
(c) distance test ( m) is inset expanded view of nondeterminism, and (d) interference test, with nondeterminism
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