Radio Resource Management(RRM) is a hard topic to understand. Following videos from Jerome Henry will help you a lot to get an overview of this topic. I highly recommend view these few times to get an overview of this topic & then read config guides and any other material as things go into deep.
This is how I understand this this topic.
RRM enables controller to monitor their associated AP for the following information.
1. Traffic Load (how many clients in a given AP)
2. Interference (coming from other 802.11 soruces)
3. NOise (non-802.11 that interfere with current CH)
4. Coverage (RSSI & SNR for all connected CH)
5. Other APs (number of nearby AP)
Using this information RRM can periodically re-configure 802.11 RF network for best efficiency. To do this RRM perform following functions.
1. Radio Resource Monitoring :- AP goes off-channel for a period not greater than 60ms to monitor all channels for noise & interference.
2. Transmit Power Control (TPC) :- WLC dynamically control AP tx power based on real-time wireless condition. In most cases TPC seeks to lower the AP tx power to reduce interference. In certain cases (sudden lost of a AP). TPC can increase power of a surrounding AP. Controllers needs to be in same RF group in order to do this properly
3. Dynamic Channel Assignment (DCA) :- Consider AP Rx Energy, Noise, 802.11 interference, Utilization & Load to handle DCA.
4. Coverage Hole Detection & Correction (CHDC) :- This is done by per controller (no interaction with other WLC to make a decision). Depend on the RSSI of a client it will determine coverage hole (no another AP for client to roam) & determine whether it can be corrected or not. If it can be corrected, WLC increase the power of AP.
Following are few key points to remember about RRM.
1. RRM Neighbour Messages send by each AP in every 60s all connected channels.
2. These msg send in lowest mandatory data rates with max power.
3. RF leader elected if multiple WLC in a given mobility group & who will perform RRM calculations & responsible for TPC & DCA.
4. WLC & AP use the configured RF group name to determine whether they are part of same RF group.
5. In WLC 220.127.116.11 onwards RF Group Leader can be configured Statically (otherwiese Auto elected)
6. RRM startup mode run 100 minutes ( every 10 min or 600s) with high sensitivity. After that it will run as the specified interval & sensitivity.
7. Max 20 WLC & 1000 AP can be part of a RF Group.
Each of them are important & I will try to do a separate post for each of them.