You're right, PMP450m is capable of carrying additional downlink traffic when the Frame Utilisation
reaches 100%. The 100% figure simply means that all of the downlink slots are carrying data - MU-MIMO
operation permits these slots to carry data to more than one SM at the same time. I tend to think of this
as stacking more data in each downlink slot.
I posted some diagrams a while back to illustrate MU-MIMO operation:
For non-MU-MIMO systems Frame Utilisation is a good indication of congestion. However, with
MU-MIMO the amount of additional data is dependent on a number of factors - including the
spatial arrangement of the SMs which require data at any particular time. The Statistics -> Frame Utilization
tab highlights this in the Spatial Utilisation table - you can gauge the congestion particular directions
from this. MU-MIMO significantly increases the sector capacity but the simple Frame Utilisation
figure becomes a less useful indicator of congestion.
It may be that the PMP450m is simply meeting the demand.
This post contains more information about the MU-MIMO metrics:
If you are able to capture some field diagnostics (http://AP_IP_ADDRESS/field_diags.cgi) during a busy time
on your sector I would be happy to review them.