I do not think there is greater details of how exactly it is calculated.(at these are cisco proprietary algorithm). Here is the detail I could find in RRM whitepaper that should helps you
https://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/8-3/b_RRM_White_Paper/b_RRM_White_Paper_chapter_0100.html
1 Same Channel Contention—other AP's/clients on the same channel - also known as Co-Channel
interference or CCI
2 Foreign Channel - Rogue—Other non RF Group AP's operating on or overlapping with the AP's served
channel
3 Noise—Non-Wi-Fi sources of interference such as Bluetooth, analog video, or cordless phones - see
CleanAir for useful information on using CleanAir to detect noise sources
4 Channel Load—through the use of industry standard QBSS measurements - these metrics are gathered
from the Phy layer - very similar to CAC load measurements.
5 DCA Sensitivity—A sensitivity threshold selectable by the user that applies hysteresis to the evaluation
on channel changes
The impact of each of these factors is combined to form a single RSSI based metric known as the Cost Metric
(CM). The CM then represents complex SNIR of a specific channel and is used to evaluate the throughput
potential of one channel over another. The goal is to be able to select the best channel - for a given AP/Radio
while minimizing interference . Using the CM, the Group Leader is able to evaluate every AP and every
channel for maximum efficiency.
HTH
Rasika
**** Pls rate all helpful responses ****
