Image Processing Reference
In-Depth Information
•
WLAN technology can provide the communications services for distributed control
applications involving mobile subsystems like autonomous transport vehicles, robots, or
turntables.
•
Implementation of distributed control systems in explosible areas or in the presence of
aggressive chemicals.
•
Frequent plant reconfiguration gets easier as fewer cables have to be remounted.
•
Mobile plant diagnosis systems and wireless stations for programming and on-site
configuration.
However, when adopting WLAN technologies for the factory floor some problems occur. The first
problem is the tension between the hard reliability and timing requirements (hard real-time) per-
taining to industrial applications on the one hand and the problem of wireless channels having
time-variable and sometimes quite high error rates on the other. A second major source of prob-
lems is the desire to
integrate
wireless and wired stations into one single network (henceforth called
a
hybrid system
or
hybrid network
). This integration calls for the design of interoperable protocols
for the wired and wireless domains. Furthermore, using wireless technology imposes problems not
anticipated in the original design of the (wired) fieldbus protocols: security problems, interference,
mobility management, and so on.
In this chapter we survey some issues pertaining to the design and evaluation of protocols and
architectures for (integrated) wireless industrial LANs and provide an overview of the state of the
art. here is emphasis on aspects influencing the time and reliability behavior of wireless transmis-
sion. However, we discuss not only the problems but also present different solution approaches on
the physical, medium access control (MAC), or data-link layer. These layers are key to the success
of wireless fieldbus systems because they have important responsibilities in fulfilling timing and
reliability requirements, and furthermore they are exposed most directly to the wireless link char-
acteristics. In the second part of this chapter, we focus on technologies and the creation of hybrid
systems. On the one hand, there are a number of existing fieldbus standards like controller area net-
work (CAN), factory instrumentation protocol (FIP)/WorldFIP, or PROFIBUS. For these systems we
discuss problems and approaches to create hybrid systems. On the other hand, one could start from
existing wireless technologies and ask about their capabilities with respect to timeliness and reliabil-
ity. he most widely deployed WLAN technology is currently the IEEE . WLAN standard and
its suitability for industrial applications is discussed.
This chapter is structured as follows: In Section . important general considerations and
problems of wireless industrial communications and wireless fieldbus systems are presented. In
Section ., we discuss some basic aspects of wireless LAN technology and wireless wave prop-
agation. The transmission impairments resulting from certain wave propagation effects and some
physical layer approaches to deal with them are presented in Section .. Wireless wave propa-
gation has also some interesting consequences on the operation of the MAC and data-link layer,
thesearediscussedinSection..hefollowingtwosections,Section.and.,takeamore
technology-oriented perspective. Specifically, in Section . we survey the state of the art regarding
wireless industrial communication systems and wireless fieldbus systems. In Section . we present
the important aspects of the IEEE . WLAN standard with respect to transmission of real-time
data. Finally, in Section . we provide a brief summary.
The chapter restricts to protocol-related aspects of wireless transmission, other aspects like sig-
nal processing, analog and digital circuitry, and energy aspects are not considered. here are many
introductory and advanced topics on wireless networking, for example, [,,,,,,,].
Several separate topics in wireless communications are treated in []. Furthermore, this chapter
is not intended to serve as introduction to fieldbus technologies, some background information can
be found in [,].
