Aerohive access point, Руководство по развертыванию

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Chapter 4 The HiveAP 340 Platform
58 Aerohive
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 HiveAP 340, 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.
1
Using two or three transmit and receive chains simultaneously increases the 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
Figure 7 .
Figure 7 Antennas and radios
The wifi0 interface links to radio 1 (frequency range = 2.4 GHz for IEEE 802.11b/g), and the wifi1 interface links to
radio 2 (frequency range = 5 GHz for IEEE 802.11a). These interface-to-radio relationships are permanent.
When deciding how many antennas to use, consider the types of wireless clients—802.11n only, 802.11g/n,
802.11b/g/n, or 802.11a/n—the area needing coverage, and the RF environment.
1. The convention for presenting the configuration of transmitting and receiving MIMO RF chains is TxR. For
example, a HiveAP 340 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.
PWR ETH1 ETH0 WIFI1 WIFI0
Radio 1
RF 802.11b/g/n
2.4 GHz
Radio 2
RF 802.11a/n
5 GHz
2.4 GHz (A)
2.4 GHz (B)
2.4 GHz (C)
5 GHz (A)
5 GHz (B)
5 GHz (C)
RP SMA
Connectors
RP SMA
Connectors
Cut-away view of the HiveAP 340 to show the relationship of the antennas and the two internal radios