Xirrus XR-520, Руководство пользователя

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Wireless Array
40 Installing the Wireless Array
802.11a/b/g radios, and degraded performance. In 802.11n and 802.11ac, these
signals are used to enhance performance.
Figure 18. MIMO Signal Processing
802.11ac increases the number of antennas and spatial streams from a maximum
of four in 802.11n to a maximum of eight, contributing to much higher maximum
data rates (up to 6.93Gbit/s). The spatial streams can be concurrently allocated to
more than one receiving device when the AP operates in multi-user MIMO mode
(MU-MIMO, see the next section).
MU-MIMO (Multi-User Multiple-In Multiple-Out)
MU-MIMO (multi-user multiple-in/multiple-out) signal processing uses multiple
antennas on the transmitter and receiver operating on the same channel. With
spatial multiplexing in 802.11ac, up to 8 data streams may be concurrently
transmitted. MU-MIMO’s innovation allows the streams to be split between
multiple devices at once.
With 802.11n, whenever the IAP transmitted data, all of the traffic at any instant of
time was directed to a single client. As a consequence, if a set of devices included
a mix of fast and slow client clients, the fast traffic was often substantially delayed
by the transmission to slower clients. 802.11ac MU-MIMO works by directing
some of the spatial streams to one client and other spatial streams to other clients,
up to four at a time
For example, in the figure below, the transmitter has four antennas. Three are
transmitting to an 802.11ac laptop that has three antennas, while the remaining
Frequency Across Subcarriers
Attenuation
Antenna 1 Signal
MIMO Processed Signal
Antenna 2 Signal
Antenna 3 Signal
Receiver