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Radio Transmit Power for Cisco Aironet Controller based APs



Radio transmit power is configurable on Cisco Aironet access points. The maximum power is determined by the regulatory agency in the country of operation and is set during manufacture of the access point. In the United States, the 802.11abgn radios transmit at a maximum of 100 mW when multiple antennas are selected (the default mode). However, it is rarely desirable to deploy APs with their transmit power set to 100mW because there is no additional power available to handle coverage holes if a neighboring AP fails.

The AP Radio Transmit power setting significantly impacts the coverage of the AP (i.e. "cell size"). In general, using higher power levels will increase the range in which clients can associate with the access point. In contrast, using lower power levels will reduce both the AP cell size and interference between cells and increase the capacity of the wireless LAN.

Cisco Aironet access points also support Dynamic Transmit Power Control (DTPC). With DTPC, you can limit the transmit power level of client devices that associate to the access point and support Cisco Compatible Extensions (CCX). When a client device associates to the access point, the access point sends the maximum power level setting to the client. This can improve battery life of client stations and help to secure communications from the client station. DTPC is only supported on Cisco- and CCX-compliant wireless client adapters. Over 90% of enterprise wireless client devices support the CCX program. Motorola and many other key third-party manufacturers participate in the CCX program as well.

Cisco Unified Wireless Network solutions can configure APs for Radio Resource Management (RRM) to automatically adjust both power and channel settings. This is a dynamic solution that automatically adjusts to changes that occur in your RF environment without engineer interaction. The system intelligently modifies access point settings as needed, increasing power for coverage hole detection, decreasing excessive power, and changing AP channels if significant RF interference occurs, such as when a neighboring store brings up a new access point.


Cisco Wireless LAN Controller Configuration Guide:- Configuring Radio Resource Management


This is a great post, as information about DTPC and CCX support seems to be quite difficult to find.

I have a few questions about client power levels and DTPC/CCX support:

1. How do I tell if my client  wireless NIC supports CCX (and which version)?

2. Is it the wireless NIC hardware that supports CCX functionality, or its driver (or maybe the wireless client software itself)?

3. DTPC used with clients which support CCX v2 or above would seem to be a great way to mitigate CCI caused by clients in high density deployments, but is not mentioned in any Cisco high density deployment guides. Is there any reason for this?

4. Is DTPC (through CCX support) available in many current tablets and smartphones, or has it mainly been built in to laptop wireless NICs?

Thanks again for the great post.


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