MSM7xx Controllers Configuration Guide v6.4.0

Using three frequencies to cover a large area in North America. Gray areas indicate overlap
between two cells that use the same frequency.
Distance between APs
In environments where the number of wireless frequencies is limited, it can be beneficial to adjust
the receiver sensitivity of the AP. To make the adjustment, select Controlled APs >> Radio
management > Radio configuration > [radio] and set the Distance between access points option.
For most installations, Distance between access points should be set to Large. However, if you are
installing several wireless APs and the channels available to you do not provide enough separation,
reducing receiver sensitivity can help you to reduce the amount of crosstalk between wireless APs.
Another benefit to using reduced settings is that it improves roaming performance. Wireless users
switch between APs more frequently.
Automatic transmit power control
The automatic power control feature enables the AP to dynamically adjust its transmission power
to avoid causing interference with neighboring HP APs. For information see “Transmit power
control” (page 99).
Supporting 802.11a and legacy wireless clients
The 802.11n standard is very similar to the 802.11g standard, in that both provide mechanisms
to support older wireless standards. In the case of 802.11g, protection mechanisms were created
to allow 802.11b and 802.11g wireless devices to co-exist on the same frequencies. The data
rates of 802.11g (6, 9, 12, 18, 24, 36, 48 and 54 Mbps) are transmitted using Orthogonal
Frequency Division Multiplexing (OFDM) modulation, while the data rates of 802.11b are
transmitted using Direct Sequence Spread Spectrum (DSSS) modulation. Since older 802.11b-only
clients cannot detect OFDM transmissions, 802.11g clients must “protect” their transmissions by
first sending a frame using DSSS modulation. This frame – usually a CTS-to-self or RTS/CTS exchange
– alerts 802.11b clients to not attempt to transmit for a specified period of time.
If protection is not used, 802.11b clients may transmit a frame while an 802.11g frame is already
being sent. This leads to a collision and both devices need to re-transmit. If there are enough
84 Wireless configuration