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interaction with the reflected radio waves can cause a drop in signal strength,
or even cause it to be cancelled out completely. Transmission quality can be
improved with so-called "diversity" methods. The principle of "diversity"
methods relies on the fact that a transmitted signal is often received multiple
times (generally twice).
Each wireless LAN module is equipped with two send/receive units, each of
which can be connected to an antenna. In the case of antenna diversity, the
WLAN module checks which send/receive unit (antenna) is receiving the
strongest signal from a client. Only the stonger signal is used. The Access
Point stores the information on which send/receive unit was used to receive
data and proceeds to use the same unit for the transmission to the client.
Antenna diversity ensures that the various clients associated with the Access
Point always use the send/receive unit with the best signal.
7.1.2
Polarization diversity
Other diversity techniques process the two signals and combine them into a
single signal. The most common methods are space diversity and polarization
diversity. LANCOM Systems supplies various polarization diversity antennas
for connection to LANCOM devices. With these models, two orthogonally
polarized signals are received at a transmitter/receiver unit and combined to
form a single signal which is stronger than the two individual signals. This
improvement is the polarization gain. Further information about this techni-
que is available in our "Polarization Diversity" techpaper.
7.1.3
MIMO
MIMO also uses polarization antennas which can process two orthogonally
polarized signals. Different to polarization diversity, MIMO uses each of these
signal to transport a separate data stream and acheive twice the data
throughput.
7.1.4
Installing the AirLancer Extender antennas
The following diversity antennas are available as accessories for the LANCOM
OAP Wirelesss:
AirLancer Extender O-D80g (2.4 GHz band ), item no. 61221
AirLancer Extender O-D60a (5 GHz), item no. 61222
AirLancer Extender O-D9a (5 GHz), item no. 61224
LANCOM OAP-54 Wireless and LANCOM OAP-310agn Wireless
Chapter 7: Options and accessories
85
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