Cisco 8821 Manual page 48

Individual access points can be configured to override the global setting to use dynamic channel and transmit power assignment
for either 5 or 2.4 GHz depending on which frequency band is to be utilized.
Other access points enabled can be enabled for Auto RF and workaround the access points that are statically configured.
This may be necessary if there is an intermittent interferer present in an area.
The 5 GHz channel width can be configured for 20 MHz or 40 MHz if using Cisco 802.11n Access Points and 20 MHz, 40
MHz, or 80 MHz if using Cisco 802.11ac Access Points.
It is recommended to use channel bonding only if using 5 GHz.
It is recommended to utilize the same channel width for all access points.
Cisco Wireless IP Phone 8821 and 8821-EX Wireless LAN Deployment Guide
48