Rate 8X/6X MIMO-B but no 256qam?

Something that i've  been wondering i have a CPE that we are using for our test at one of our staff taht has -60 RSL and is showing up as VC 18 Rate 8X/6X MIMO-B 

But when i check his actual modulation quality he doesn't seem to be getting 8X 256-qam

Why would this be? I mean sure he gets 256 once in a while as you can see in the below test this test hapeend to have 59 packets in 256 but thats not really an 8X connection is it?

Link Quality

RF Path Modulation Fragments ModulationPercentage Average CorrectedBit Errors

V QPSK 52341 33% 0.045
V 16-QAM 52348 33% 0.054
V 64-QAM 52325 33% 0.049
V 256-QAM 59 <1% 8.949
H QPSK 52313 33% 0.093
H 16-QAM 52307 33% 0.121
H 64-QAM 52292 33% 0.150
H 256-QAM 25 <1% 10.280


RF Path Modulation Fragments ModulationPercentage Average CorrectedBit Errors

V QPSK 11901 33% 0.179
V 16-QAM 11903 33% 0.210
V 64-QAM 11896 33% 0.190
V 256-QAM 7 <1% 10.857
H QPSK 11894 33% 0.737
H 16-QAM 11893 33% 0.871
H 64-QAM 11893 33% 0.954
H 256-QAM 1 <1% 11.000

When it says "8X/6X" it means that 8X is the maximum possible modulation level for that device, and 6X is the current stable modulation being used, which is 64QAM.

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Is that what that means, Eric? I always interpreted it like DL/UL!

Makes more sense...

At any rate, the answer I've always had from Cambium is to disregard the *X thing from the front page anyway as it's inaccurate most of the time. Real answer is in the link efficiency tests like you see. based on the table you provided, the SM is capable of running briefly at 256QAM but the error rate is better at 64QAM. On a slightly worse link, 256QAM won't show at all.

Based on your table I'd speculate that there's some minor interference on the horizontal polarity, minor enough that it's only affecting higher modulations.

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Just a few notes...

1. On the older PMP100 equipment, if you had a P8 radio, it was only capable of 1X modulation, so on both the SM and the AP sessions page it would say "1X/1X" even though all the other radios would say "2X/2X" or "2X/1X"

2. It doesn't make sense that the downlink would ALWAYS be showing 8X, regardless of the actual signal quality. The uplink and downlink modulations are shown on their respective radios... e.g. on the SM, when it shows "8X/6X", it means that it is able to transmit to the AP reliably at 6X aka 64QAM modulation... so this would be the 'uplink'. The reverse is true when you review the sessions tab on the AP, it will show you what the downlink is to each client.

3. A Cambium staff member 'liked' my post... I'd be surprised if he liked an incorrect or misleading post :-)

4. I believe you're right in your diagnoses of Chris's issue, i.e. he's experiencing a little interference and if he moved to a cleaner channel OR increased his SnR, he'd send more packets via 8X.

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