Product and Software: This article applies to Aruba AP-125 and ArubaOS 3.3.2.x and later.
The AP-12x ARM Coverage indices are calculated per 20MHz channel as with legacy Aruba APs. All 20MHz HT clients and legacy clients still only use the primary channel. Therefore, the utilization of the 40MHz channel might be a small fraction of the total time (based on number of clients connected with 40MHz capability).
For ARM Interference indices, the AP-12x assigns a weight to the secondary channel when it hears an AP advertising 40MHz service to account for this potential 40MHz activity, which will interfere with traffic on the secondary channel.