Aerohive Networks AP121 Hardware Reference Manual page 74

Figure 7 2x2 MIMO (2 transmit antennas x 2 receive antennas)
802.11n wireless client
with two antennas
RF chains
Digital signal
processors
Data
In previous 802.11 standards, access points and clients each employed a single set of components, or RF
chain, for transmitting or receiving. Although two antennas are often used for diversity, only the one with the
best signal-to-noise ratio is used at any given moment, and that antenna makes use of the single RF chain
while the other antenna remains inactive. A significant improvement that MIMO introduces is to permit each
antenna to have its own RF chain and for all antennas to function simultaneously. For the AP340, you can
connect up to three antennas per radio and configure the radio to use two or three transmit chains and two
or three receive chains.
amount of data that can flow across the WLAN and accelerates the processing of that data at each end of
the wireless link.
Another major aspect of MIMO is how it turns multipath signals from a curse to a boon. As a radio signal
moves through space, some objects reflect it, others interfere with it, and still others absorb it. The receiver
can end up receiving multiple copies of the original signal, all kind of muddled together. However, the
digital signal processors in the multiple receive chains are able to combine their processing efforts to sort
through all the received data and reconstruct the original message.
Furthermore, because the transmitter makes use of multiple RF chains, there is an even richer supply of
signals for the receive chains to use in their processing. To set the transmit and receive RF chains for a radio
profile, enter the following commands:
radio profile <name> transmit-chain { 2 | 3 }
radio profile <name> receive-chain { 2 | 3 }
There are two sets of antennas—three antennas per set—that operate concurrently in two different
frequency ranges: 2.4 GHz (IEEE 802.11b/g/n) and 5 GHz (IEEE 802.11a/n). Using two different frequency
ranges reduces the probability of interference that can occur when numerous channels operate within the
same range. Conceptually, the relationship of antennas and radios is shown in
1. The convention for presenting the configuration of transmitting and receiving MIMO RF chains is TxR. For
example, an AP340 radio functioning in access mode might be configured to use two RF chains for
transmitting and three for receiving. In that case, its configuration can be presented as "2x3". In general,
the number of receive antennas is equal to or greater than the number of transmit antennas.
Hardware Reference Guide
RFsignals
(multipath object)
Transmit
antennas
1
Using two or three transmit and receive chains simultaneously increases the
AP340 P
AP340 using two
RF chains
Receive Digital signal
antennas processors
Figure 8 on page
O
RODUCT VERVIEW
antennas
Reassembled
data
74.
73