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DTUS065 rev A.7 – June 27, 2014
802.11n uses these bounces to allow several independent streams (2 to 4) to
be sent and identified simultaneously. At the beginning of the transmission,
a well-known pattern is sent. The receiver uses that pattern to calibrate itself
and characterize the transmission channel for each antenna.
Using that information, the receiver is able to calculate which stream
belongs to what antenna.
In this case there must be at least one antenna per stream to be sent.
Supernumerary antennas are used to transmit additional spatial information.
Since 802.11n uses bounces to increase bandwidth, a line of sight outdoor
application will have poor performances compared to an indoor one, because
there are potentially no bounces at all. This problem can be solved by
sending polarized radio waves orthogonal to each other. Such so-called
“Slant Antennas” are actually made of 2 specifically polarized antennas put
together in a single case.
III.4
Radio channel choice
Wi-Fi standard compliant products can use two RF bands.
-
The 2.4 GHz band covers the channels compatible with 802.11b/g/n
standards
-
The 5 GHz band covers the channels compatible with 802.11a/n/ac
standards
Products performance is affected by the radio link quality (a.k.a. RSSI). The
better the RSSI is, the better the throughput and error rate can be.
A preliminary site survey is strongly recommended to detect overloaded
radio channels BEFORE buying band specific antenna.
An overloaded channel may strongly affects performances. It is
recommended to use a free channel.
