MSM7xx Controllers Configuration Guide v6.4.0

How it works
In the 5 GHz band, auto-channel attempts to choose the best operating channel based on achieving
the following goals:
• Minimize co-channel operation by avoiding the use of the same channel as on neighboring
radios.
• Minimize adjacent channel interference on neighboring radios. For example, channels 36
and 40 are adjacent channels. There will be interference if radios using these channels are
near each other.
• Operate at the highest transmit power. In different regulatory domains (countries), the allowed
transmit power may vary for different channels. (For example, in North America, the limits for
channels 36 and 40 are lower than for channel 100.)
• Have minimal non-802.11 RF noise.
• Use a non-DFS channel, if it provides the same benefits as using a DFS channel.
• Try to use all available channels in the 5 GHz band equally across all radios managed by
the system as a whole.
In addition, there are considerations for 20/40 MHz channel widths:
• Choose channels consistent with the channel-width configured on a radio, and account for
the fact that external APs may also be operating in 20 or 40 MHz widths.
• Choose channels to align the primary-channels. (E.g., channels 36+ and 40- are 40 MHz-wide
channels which use the same RF frequencies, but differ in their primary channel.)
In the 2.4 GHz band:
• Auto-channel prefers the standard non-overlapping channels (1, 6, 11 in the US and 1, 7,
13 in Europe). If channel 13 is excluded (in the exclusion list) in a regulatory domain which
normally allows it, then the US channel set (1, 6, 11) is used. This was done to support
deployments in Europe that service US visitors. US devices generally cannot operate on channel
13. (If all but four channels are excluded, then auto-channel will switch to a four-channel plan.
For example, if all channels except 1, 5, 9, and 13 are excluded, then auto-channel will only
use those four channels.)
• Auto-channel prefers sharing a channel rather than choosing a channel that (potentially)
overlaps two other in-use channels.
Auto-power (system-wide)
The system-wide auto-power feature will only adjust the power on controlled AP radios that have
the Automatic power control option enabled on the Radio configuration page.
Auto-power can only be enabled if Auto-channel is enabled. The auto-power algorithm is run after
auto-channel.
The goal of auto-power is similar to auto-channel (maximize the wireless capacity and fair-share
access), but auto-power also needs to minimize the possibility of coverage holes. The auto-power
algorithm only considers non-fixed-power radios. Radios on non-controlled APs, as well as those
on controlled APs that do not have the Automatic power control option enabled on the Radio
configuration page, are considered fixed power (unchangeable) and are not optimized by
auto-power.
Lowering the power on a radio reduces the area it covers and can leave a hole in the wireless
network if a radio does not have many neighbors. Therefore, auto-power will only reduce the
power to a radio if it has several neighbors providing overlapping coverage. Expect power
adjustments for radios with four or more neighbors operating nearby.
The auto-power scan will also detect cases where radios are so close together that even with power
adjustment, co-channel interference cannot be eliminated. In these cases, auto-power will only
adjust the power of these two radios if the interference with more distant co-channel neighbors
190 Radio Resource Management