Image Processing Reference
In-Depth Information
25.2 WLAN, WPAN, WSN, and Cellular and Ad Hoc Networks
The expressions WLAN, WPAN, and cellular and ad hoc networks are commonly used, often though
without consistency and/or precision. In industrial contexts additionally WSN play a role and are
also not always clearly distinguished from WLANs and WPANs. In the following, a clarification of
the terminology is given.
WLAN
: A wireless LAN has the same functionality as a wired LAN with the difference that the wires
are replaced by air links. his means that within a specific area (home, office, hot spot), intercommu-
nication between all devices connected to the network is possible. WLANs are associated with data
communication and “large” data rates. The definition of WLAN says nothing on how the network
is organized. Often an infrastructure of mounted access points (APs) enables wireless access to the
wired LAN behind the APs thus representing a cellular network structure. Nevertheless, a wireless
LAN can also function on an ad hoc basis.
WPAN
: In a WPAN also all devices are interconnectable. he difference is that all units are somehow
associated to someone or something (a person, a robot, a specific shared or public devices). (W)PANs
are associated with smaller scales concerning distance as well as amount of traic. A PAN can consist
of a variety of devices and can even comprise different technologies. he type of traffic is not decisive.
InaPAN,dataaswellasvoicecommunicationcanprevail.
While you move
within
the WLAN, you can generally move
with
your WPAN. This means that
several independent WPANs possibly coexist in the same area, each being self-sufficient without any
infrastructure. Because of the lack of central control, the overall network perspective is ad hoc based,
though each individual PAN can be centrally organized.
WSN:
In contrast to LANs or PANs, WSNs are not focussed on individual traffic between individual
units but all devices are unified in the same task [Wil]. Traffic is mainly uplink from sensor to cen-
tral unit and it is often transmitted without requesting acknowledgments [ACKs]. Of the investigated
technologies, IEEE ../ZigBee is most suitable for WSNs. Still, while some results presented here
might be transferable to WSNs, the focus is on WLANs and WPANs.
More decisive for the radio network performance of a technology (than the range or size of
an individual network) is whether how a network is organized; with far-reaching consequences to
system design, network optimization, etc. [MZTM]. The difference between cellular and ad hoc
networks is visualized in Figure .. As can be seen, there are several steps that lead to ad hoc
networking: A “pure” ad hoc network does neither employ any infrastructure nor a specific unit
(like AP or base station) for the organization of coverage, synchronization, and services. Nev-
ertheless a network can be “ad hoc,” independent from whether it supports single or multihop
communication.
It can be seen that WLAN technologies like IEEE . in the infrastructure mode (using the
point coordination function [PCF]) are in the same classification as typical “cellular” systems like
GSM or UMTS/WCDMA; all are based on infrastructure and use a specific unit for central control.
Concerning the architecture, it would thus be correct to call these WLAN systems cellular systems.
Despite this, there are distinct differences with regard to coverage. he “wide” (instead of “local”) area
coverage of cellular systems like GSM, has caused cellular systems to be associated with complete
coverage and access everywhere, even though this is not correct. he description wireless wide area
network (WWAN) gives a better idea of the difference to WLAN systems.
Cellular systems are also associated with voice traffic, though this is also not decisive. More impor-
tant is that WWAN technologies are designed to support user mobility (and roaming) up to very high
velocities, while WLAN systems rather support stationary or portable access. Industrial setups are
generally limited to a specific area. Deploying a WWAN technology would represent an overkill and
