Wireless Array
Installing the Wireless Array 39
Up to Eight Simultaneous Data Streams — Spatial Multiplexing
Spatial Multiplexing transmits completely separate data streams on different
antennas (in the same channel) that are recombined to produce new 802.11ac data
rates. Previously used for 802.11n, the maximum number of streams for 802.11ac
has been increased to eight. Higher data rates are achieved by splitting the
original data stream into separate data streams. Each separate stream is
transmitted on a different antenna (using its own RF chain). MIMO signal
processing at the receiver can detect and recover each stream. Streams are then
recombined, yielding higher data rates.
Figure 17. Spatial Multiplexing
The date rate increases directly with the number of transmit antennas used. Note
that mobile devices in the near future will support up to three or four streams at
most, with many supporting less.
MIMO (Multiple-In Multiple-Out)
MIMO (Multiple-In Multiple-Out) signal processing is one of the core
technologies of 802.11n and 802.11ac. It mitigates interference and maintains
broadband performance even with weak signals.
Prior to 802.11n, a data stream was transmitted via one antenna. At the receiving
end, the antenna with the best signal was selected to receive data. MIMO signal
processing uses multiple antennas to send and receive data. It takes advantage of
multipath reflections to improve signal coherence and greatly increase receiver
sensitivity (Figure 18). Multipath signals were considered to be interference by
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