Lancom OAP-54 Manual page 15

LANCOM OAP-54 Wireless and LANCOM OAP-310agn Wireless
Chapter 1: Introduction
by the surrounding surfaces causing a broadcast signal to reach the WLAN cli-
ent's antenna over many different paths; this is also referred to as "multipath
propagation". Each of these paths has a different length meaning that indivi-
dual signals reach the client with a different time delay.
ACCESS POINT
These time-delayed signals interfere with each other at the WLAN client and
significantly weaken the original signal. For this reason, conventional WLAN
networks should always have a direct line of sight (LOS) between transmitter
and receiver in order to reduce the influence of reflections.
MIMO technology transforms this weakness in WLAN transmission into a
strength that allows an enormous increase in data throughput. As mentioned
above, it is virtually impossible to transmit different signals on the same chan-
nel simultaneously as the receiver cannot distinguish between them. MIMO
uses the reflection of electromagnetic waves and the associated spatial aspect
to obtain a third criterion for identifying the signals.
A signal sent by transmitter A and received by receiver 1 follows a different
path than a signal from transmitter B to receiver 2. Due to the different reflec-
tions and changes in polarization that both signals experience along their
paths, each of these paths takes on its own characteristics. When data trans-
mission starts, a training phases records the characteristics of the path by
transmitting standardized data. Subsequently, the data received here is used
to calculate which data stream the signals belong to. The receiver decides for
itself which of the incoming signals is to be processed, thus avoiding loss from
interference.
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WLAN-Client