Understanding Auto Tune Power Policy for Wireless Radios

The amount of power an access point uses affects the coverage area of the wireless network. The higher the power level on access points, the larger the coverage area of a wireless network. Usually, you want your wireless network to cover all areas, but with minimal overlap between access points that share the same channel—this minimizes co-channel interference. Configuring each access point radio’s power manually can be time consuming and tedious for a large installation. For one thing, in order to ensure complete coverage while minimizing co-channel interference, you need to consider nearby access points sharing the same channel as well as understand signal propagation issues. For example, the walls and windows in your facility affect signals. Instead of manually configuring power, you can configure access points to automatically tune their radios' power based on RF data they collect about neighboring access points. With automatic power tuning, which is configured in the Network Director Radio profile under the Power & RF Settings tab, access points adjust their radios’ power levels automatically, based on the power levels of all neighboring access points.

Radios get most configurations, including power tuning, from the associated Radio profile. For directions to create a Network Director Radio profile, see Creating and Managing a Radio Profile.

Note: Automatic channel tuning is also available, and automatic power tuning and channel tuning can be used together. For more information about automatic channel tuning, see Understanding Adaptive Channel Planner.

This topic describes:

How Does Wireless Transmit Power Work?

Transmit power, like other sound pressure, is measured in decibels. Because the measurement is logarithmic instead of linear, an increase of 6 dB will double the range of coverage of a radio. Valid power values depend on the country of operation. The default transmit power on all access point radio types is either the highest setting allowed for the country of operation or highest setting supported on the hardware, whichever is lower.

How Does Auto Tune Power Policy Work?

Power tuning computation is performed on the access point itself without any help from the controller. Access points listen for nearby access points on the same channel and then adjust their power to provide good coverage while avoiding co-channel interference.

The power tuning algorithm automatically adjusts to changes when needed, for example when one access point is removed.

Auto-tuned power settings are not persistent—auto-tuning must be enabled for the changes to occur. If you turn off auto-tuning, the access point will go back to the configured power setting.

When is Auto Tune Power Policy Most Helpful?

When an access point radio is first enabled, automatic power tuning can assign initial power settings compatible with surrounding access points.

How Do I Turn Off an Auto Power Policy?

You can turn off automatic power tuning by editing Radio Profiles—this turns off auto power for all access points using the Radio Profile. See Creating and Managing a Radio Profile.You can also turn off automatic power tuning for a single radio when you add or edit an individual access point—for directions, see Adding and Managing an Individual Access Point.

What Changes Can I Make to an Auto Tune Power Policy?

When power tuning is enabled in a Radio profile, you can change the wireless transmit power backoff timer, power tuning interval and the power ramp interval for that Radio profile.

Transmit Power Backoff Timer changes the interval at which radios reduce power after temporarily increasing the power to maintain the minimum data rate for an associated client. At the end of each power-backoff interval, radios that temporarily increased their power reduce it by 1 dBm every 10 seconds. The power backoff continues in 1 dBm increments after each interval until the power returns to expected setting.
Power Tuning Interval is the number of seconds between reevaluations of power. Power changes can only take place after an evaluation or when an anomaly occurs. You can change the wait interval between evaluations from the default 600 seconds.
Power Ramp Interval is the rate at which power is increased or decreased on radios in a Radio profile until the optimum power level calculated by RF auto-tuning is reached. You can change the 1 dBm increment to increase and decrease in larger or smaller steps.