Wireless Interface Configuration
Adaptive Tx Power Control
N o t e
This mode is recommended for low density deployments where coverage
holes may be of concern. The data transmit power attenuation is calculated
to put transmissions into the noise floor of the nearest same-channel AP, then
reduced if needed to reach the farthest associated client station at a target
In dense deployments without the ability to load balance clients, this mode
could increase the risk that long reaches might increase contention.
Some "highly mobile" WiFi devices (such as VOIP telephones, SVP telephones,
and other clients with special drivers) employ an "aggressive roaming" mech-
anism that is sensitive to varying power levels of data frames. The variable
data frame power levels in AP+Clients mode may cause these devices to
prematurely roam to another AP. It is recommended that a wireless deploy-
ment servicing highly mobile clients use AP adaptive mode in a dense deploy-
ment of APs.
Power Reduction Limit
Setting the Transmit Power Reduction Limit determines the minimum power
level of the radio. This value, combined with the radio's Tx Power Reduction
setting, establishes the range of Transmit Power adjustments in ATPC. How
this setting is tuned depends on the ATPC scope and adaptive mode selected.
The radio's Tx Power Reduction setting, not the radio's Max Tx Power,
determines the maximum transmit power of the radio. ATPC may reduce that
further, up to the relative limit specified in the Transmit Power Reduction
For example, if a radio's Max Tx Power is 18dB, and Tx Power Reduction is
set to 3dB, then for ATPC purposes, the maximum power level is 15dB. If the
Tx Power Reduction Limit is set to 5dB, ATPC will adapt the radio's power
level within the range of 10 and 15dB.
Adaptive Tx Power Control is not a substitute for an RF site survey. Channel
planning is still required to take maximum advantage of non-overlapping RF
coverage. Access points should be placed to provide maximum line-of-sight
coverage, with a density that ensures that there are no gaps and that the
furthest client can be reached.