Not sure how to describe it, but with each and every FW release (on 5.9.0 now) I still seem to see that 40mhz performs better % wise on DL than 80mhz on 4625/4525 SMs. This is using TDD 75/25 5ms with Long GI.
What I mean is that if you take the maximum calculated values using the ePMP Capacity Planning Tool for 40mhz and 80mhz and then compare it to actual SM performance you will find that 40mhz comes much closer to the calculated capacity than 80mhz does.
My test setup is a 4500L AP connected to a single 4525 SM around 500ft away outdoors with MCS11 on DL/DL with SNR of 52/50. Performance stats show it keeps 99.9% of the time MCS 11 on DL and 83% on MCS 11 when on UL.
I do a 20 second link test to SM and get 365 DL/116UL. Planning Tool calculates 414DL/127UL for this link. So, on this I get around 88% of max on DL and 91% of max on UL.
When switching to 80mhz on the same link test I get 635DL/254UL. Planning tool calculates 860DL/266UL. That means I get only 73% of max on DL, but 95% of max on UL.
The tests above are on what I call and ideal link. Very short range, great signal/modulation and near zero noise on the SM side, but according to spectrum analyzer there is decent noise on the AP side.
However, on a real world 4600 setup with 3 SMs of various signals and distances I still feel performance on 80mhz does not live up to expectations.
Now for this setup I set the Planning tool with interference levels of -89 AP and -92 SM to simulate some noise the AP seems to be showing.
On a 20s link test to my best client with the AP mostly idle (<5mbps) I get 583DL/140UL. The CPE is doing MCS11 DL but is set to a max of MCS9 on UL due to AP side noise and how the SM performance stats show it TX at the most.
Planning tool shows this SM should get around 777DL (MCS11) and 170UL (MCS9). That means I am getting around 75% of max on DL and 82% of max on UL.
Is this a limitation of the processor on the 4625/4525 SM being not able to really take full advantage of the larger channels above 40mhz? Meaning that the larger channel sizes will mainly show their benefit in more capacity for the AP and not necessarily in higher speeds for the SM?
It seems that might be the case as I did a Dual SM 20s link test using two CPEs with similar stats (MCS11 DL/MCS9UL) and I got a combined total of 777DL and 139UL. Using the planning tool with 2 SM it showed I should get a total AP capacity of 765DL and 151UL. That means when doing dual SMs I was getting 101% of max DL and 92% of max UL.
Now as a test I switched the 4500L AP and its single SM to WLR mode at 80mhz and got 839DL/743UL on a 20s link test. I know this is not TDD framing so it can utilize almost 100% of the frame time in either the DL or UL direction. Just adding this information as a comparative. Not trying to draw conclusions using WLR mode.