Extreme Networks Summit WM User Manual page 63

This phenomenon is called multipath. Since these streams are bounced from different surfaces, they
follow different paths to the client device. The client device, which is also 802.11n compliant, also has
multiple antennas. Each of the antennas independently decodes the arriving signal. Then each antenna's
decoded signal is combined with the decoded signals from the other antennas. The software algorithm,
uses the redundancy to extract one or two spatial streams and enhances the streams' "signal to noise
ratio".
The client device too sends out one or two spatial streams through its multiple antennas. These spatial
streams get multiplied into several steams as they bounce off the obstructions in the vicinity enroute to
802.11n AP. The 802.11n AP's MIMO receiver receives these multiple streams with three antennas. Each
of the three antennas independently decodes the arriving signal. Then each antenna's decoded signal is
combined with the decoded signals from the other antennas. The 802.11n AP's MIMO receiver again
uses the redundancy to extract one or two spatial streams and enhances the streams' "signal to noise
ratio".
By using the multiple streams, MIMO doubles the throughput.
Figure 5: MIMO in Altitude 802.11n AP
NOTE
MIMO should not be confused with the Diversity feature. While Diversity is the use of two antennas to increase the
odds that a better radio stream is received on either of the antennas, MIMO antennas radiate and receive multi-
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Summit WM User Guide, Software Version 5.3