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Factory Line - Wireless LAN
1-2
PHOENIX CONTACT
1.2
Wireless technology
Wireless technology is based on the propagation and receipt of electromagnetic waves.
These waves are not subject to wear of any kind, but respond in very different ways in terms
of propagation, dispersion, and reflection depending on their frequency. The propagation of
waves in an area is three dimensional and occurs at different strengths.
Numerous factors affect this propagation, however none of these factors can affect the
propagation to the extent that a signal is not safely detected at the receiver.
The frequency spectrum that can be used is limited by physical properties or by national
regulations. Each frequency can, depending on the transmission power, only be used once
in a specific radius around the transmitter (shared medium).
1.2.1
Wave dispersion
Every electromagnetic wave has different dispersion properties depending on its frequency.
A simple comparison can be made between wave dispersion for Wireless LAN and wave
dispersion for visible light.
Every material has a frequency-dependent attenuation, every surface material bends,
reflects, refracts, absorbs or disperses electromagnetic waves of any kind. This means that
every obstacle between the transmitter and receiver must be taken into account for data
transmission.
The emitted waves are affected by various obstacles, such as the floor, ceiling, machines,
people or vehicles, and reach the receiver via many different paths. The received waves
differ in terms of intensity, phase angle, and signal runtime. Superposition means that the
received signals are amplified or reduced. The receiver must select the best signal and the
arrival of signals on many paths must not cause problems.
WLAN
Access Point
PWR
POE
HOST
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PWR
HOST
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Figure 1-1
Wave dispersion - many paths to the receiver
WLAN
Access Point
PWR
POE
HOST
1
2
3
4
PWR
HOST
1
2
3
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