Using Mimo With Legacy Clients - Aerohive AP120 Hardware Reference Manual

Chapter A
Figure 9 Antennas and radios
RP-SMA
connectors
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.

Using MIMO with Legacy Clients

In addition to supporting up to 300-Mbps throughput per radio for 802.11n clients, MIMO (Multiple In, Multiple
Out) can improve the reliability and speed of legacy 802.11a/b/g client traffic. When an 802.11a/b/g
access point does not receive acknowledgment that a frame it sent was received, it resends that frame,
possibly at a somewhat lower transmission rate. If the access point must continue resending frames, it will
continue lowering its transmission rate. As a result, clients that could get 54-Mbps throughput in an
interference-free environment might have to drop to 48- or 36-Mbps speeds due to multipath interface.
However, because MIMO technology makes better use of multipath, an access point using MIMO can
continue transmitting at 54 Mbps, or at least at a better rate than it would in a pure 802.11a/b/g
environment, thus improving the reliability and speed of 802.11a/b/g client traffic.
Although 802.11a/b/g client traffic can benefit somewhat from an 802.11n access point using MIMO,
supporting such legacy clients along with 802.11n clients can have a negative impact on 802.11n client
traffic. Legacy clients take longer to send the same amount of data as 802.11n clients. Consequently,
legacy clients consume more airtime than 802.11n clients do, causing greater congestion in the WLAN and
reducing 802.11n performance.
By default, the AP340 supports 802.11a/b/g clients. You can restrict access only to clients using the IEEE
802.11n standard. By only allowing traffic from clients using 802.11n, you can increase the overall bandwidth
capacity of the access point so that there will not be an impact on 802.11n clients during times of network
congestion. To do that, enter the following command:
radio profile <string> 11n-clients-only
You can also deny access just to clients using the IEEE 802.11b standard, which has the slowest data rates of
the three legacy standards, while continuing to support 802.11a and 802.11g clients. To do that, enter the
following command:
no radio profile <string> allow-11b-clients
By blocking access to 802.11b clients, their slower data rates cannot clog the WLAN when the amount of
wireless traffic increases.
118
2.4 GHz (A)
Radio 1
2.4 GHz (B) RF 802.11b/g/n
2.4 GHz
2.4 GHz (C)
Cut-away view of the AP340 to show the relationship of the
antennas and the two internal radios
5 GHz (A)
Radio 2
5 GHz (B)
RF 802.11a/n
5 GHz
5 GHz (C)
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