Image Processing Reference
In-Depth Information
tasks performed on the factory floor with help of wireless transmissions are plentiful. They range
from monitoring, diagnosis, tracking of parts or vehicles, over commissioning (task assignment) to
centralized or even autonomous motion control [INS].
Depending on the task, different requirements must be met. They have to be investigated care-
fully before choosing the most suitable technology (possibly not only one). TCP/IP communication,
e.g., has no or soft real-time requirements while a Fieldbus system will have real-time requirements
in the range of - ms [INS].
he main criteria are generally throughput, delay, and reliability. In addition, cost, power consump-
tion, security, and, last but not least, availability can be important issues. From the technologies under
discussion, Bluetooth is a typical wireless personal area network (WPAN) representative. Bluetooth,
which is inexpensive, consumes relatively little power, is small in size, and supports voice and data
services. he different IEEE . variants are WLAN representatives that provide comparably high
user-data rates at the cost of a higher battery power consumption. The limited range makes IEEE
../ZigBee also rather a WPAN representative. It is limited to quite small data rates, but is at the
same time optimized for long battery life.
Note that in industrial environments the radio conditions can be specific. This is particularly
owned to the fact that on factory floors many metal objects and/or metal walls can be found. On
one hand metal shields radio transmissions, while at the same time causing, respectively, more
reflections. Measurements performed in industrial environments thus show smaller path loss coef-
ficients∗
∗
and noteworthy multipath propagations, which the systems need to be able to handle.
To be able to handle the latter is a matter of implementation. There is no indication though that
that cannot been achieved. A further speciality on the factory floor is electro magnetic inter-
ference from the machinery. It is found to drop off rapidly in the (considered) frequency range
above GHz and thus not considered further, though it can have significant impact in lower
frequency bands. Note that a certain probability nevertheless always remains that a wireless trans-
mission fails completely (e.g., because of complete shielding). Systems requiring a certain amount
of data rate within a strict time window, e.g., because they are safety related, should not be
wireless.
This chapter investigates the performances of WLAN and WPAN technologies from a radio net-
work perspective. The radio network perspective includes that not only the hazards of the physical
transmission (echoes, etc.) impact the performance but also the existence of other networks trans-
mitting in the same space and frequency range. hat means that in addition to the system inherent
parameters also factors like unit density, traffic demand, mobility, environmental changes during
deployment, interference, frequency range, etc. play a role. Thus both, the individual link perfor-
mance and the overall network capacity, should be optimized. Higher protocol layers (e.g., TCP/IP,
Fieldbus systems) are not part of the investigations. For an introduction into that topic please refer
to [WMW].
To outline the investigation and this chapter first describes in Section . basic differences
between WLAN, WPAN, cellular ad hoc networks, and wireless sensor networks (WSNs). In Sections
. through . the technologies Bluetooth, IEEE ., and IEEE ../ZigBee are described in
more detail. Each of these sections provides technical background on the technology as well as inves-
tigations on the performance of the systems and their suitability for industrial applications/factory
floor environments. Section . shows how the systems—all can be used in the same frequency
band—coexist. Section . provides a summary and the conclusion.
∗
Published measurement results are . in a pulp mill [Rug], . in an office building [BW] instead of the expected .
