Image Processing Reference
In-Depth Information
Spectral efficiency can be measured as the ratio of data rate divided by the used bandwidth.
Spectral Efficiency
E
=
D
/
B ( D , data rate in b/s; B , bandwidth in Hz)
E WISA
=
Mbit
/
s
/
MHz
This is an implementation and application independent value which enables technology comparison.
A more practical performance figure when looking at implemented solutions like WISA would be
Performance
P
=
/(
T s
/
n U
B
)
(
T s , slot time in ms);
n U , number of parallel uplinks)
=
forWISA
=
forsymmetricalsystems
P WISA
=
/(
. ms
/
MHz
)
=
. nodes/ms/MHz
The frequency usage can give an indication of the interference potential of a wanted system to other
wireless systems. A simple practical value can be derived from multiplying the time/duty cycle and
the bandwidth used
Frequency usage
F
=
T
B ( T , fraction of time; B ,bandwidth)
F WISA
MHz
This gives a very practical figure of how much of the available frequency band, here, e.g., the ISM band
as a very valuable resource is used for a certain implementation. he frequency usage should of course
always be as small as possible; nevertheless, the resulting interference depends in practice mainly on
the type of the other/victim system. Different victim systems react very different to frequency usage
by a wanted system, dependent on if they had been designed for coexistence or not. WISA, e.g., uses
in average not much more than  MHz of bandwidth continuously, e.g., in an application as defined
in Table ..
Another practical aspect of coexistence is stability. he influence of one system on another should
be as predictable as possible for automation systems. WISA has in practical applications a nearly
constant frequency usage, which is determined mainly by its downlink, thus making its effect on
other systems relatively predictable. he short uplink telegrams generate on average only low traffic
load
, even with high number of nodes and events.
Other wireless systems in addition to WISA used in industrial applications are
(<
%
)
IEEE ., WLAN: In factory automation, WLAN is applied in many plants for varying
applications. here are two typical uses:
- Access of many different applications to the plant/IT network (scanners, order data
transfer, production data transfer, network connection with, e.g., a notebook).
- Communication to AGV systems: Automated guided vehicles which fulfill trans-
port needs.
WLAN has its strength as a widespread standard allowing a large number of different clients to access
the same network. Typically delay times below  ms are not an issue here. WLAN is very susceptible
to disturbance as it has a large receiver bandwidth and its carrier sense multiple access (CSMA) and
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