4500c Omni Setup - Weird Signals and MU-MIMO

[terintamel]

I recently put up a 4500c connected to four 90deg RF Elements Asymmetrical Horns in a NW/NE/SW/SE setup.

I went out and tested to one client that was under a mile to the SW with clear LOS and got a decent signal but a little lower than expected, but that could be my antenna aim (haven’t verified). SW AP is connected to AP H1+V1. What I found at this single client was that their DL rates were very unstable when idle and would bounce between DS 11 to DS5, but were a stable DS10/11 most of the time when under load. I have not seen that on my other 100+ 4625SMs or my other 4525SMs off other towers. The other towers are all traditional 4x4 or 8x8 sector setups.

As another test I went to a different location to the NE at around 1 miles. It also had clear LOS. However the DL signal was way lower than expected, but the UL signal was as expected. DL signal was -69 with -51 UL. DL modulation rates like the other SM were unstable when the SM was idle. I thought it could be my antenna aim again, but I was confused because the SM was modulating at DS9-11 when active which should be impossible at -69 on 40mhz channel with 27SNR. Also, a single SM link test to the AP also showed that I was modulating at DS9-11 as I got over 300Mbps DL.

Is there something about using the 4500c in Omni mode where the reported signal for SMs not on connector H1+V1 on the AP get a false RX signal? The AP to the NE is connected to H3+V3.

Another confusing thing was Cambium told me that MU-MIMO does not work in Omni mode, but I was able to test and MU-MIMO was working. I know it was working because 2 SM link tests showed AP was pushing 600Mbps at 40mhz and the AP bandwidth charts showed MU-MIMO (green) traffic.

I guess to boil it down I want to know why the following.

1. Why DL mod rates were unstable when idle unlike my sector based 4525/4625 SMs
2. Why RX signal on SM connected to a horn facing the opposite direction was low, but had good rates and performance (false signal)?
3. Why does MU-MIMO work in Omni mode when Cambium said it should not work?

Right now I am not sure I will keep this setup or not based on the results I got. While the MU-MIMO working was encouraging the unstable rates and odd signals are giving me pause on this type of setup.

[terintamel]

AP is setup in TDD mode 75/25 short GI at 40mhz.

Here are photos from my tests showing the low reported signal for the one SM and also showing MU-MIMO works.

[terintamel]

I was already leaning in this direction, but since I did not get any response on if my results were expected or some type of oddity, I am removing the 4500c omni setup and going in a different direction. I was hoping this could be a good model for smaller tower sites, but too may odd things going on in my test setup to keep or expand this to other sites.

[micampo]

Could you explain this a little better: “Cambium MU-MIMO is supposed to use digital beamforming and null steering to create isolation between stations, so the access point can send different signals to different stations simultaneously. By pointing the speakers in different directions like this, enough isolation is created for MU-MIMO to work without beamforming. However, I think I should choose “split sector” instead of “omnidirectional.” I think “omnidirectional” implies omnidirectional antennas with overlapping beams.”

Since I do more or less the same thing with the ePMP3000, using 27dBi or 24dBi Ultradisd or 24dBi Ultrahord antennas for long-distance links and limited coverage up close but broad coverage in the distance (meaning, for example, the Ultradish has a 5-degree beam).

Would MU-MIMO work for me if I separate the Ultradishes?

I’m currently using the omni/split sector option.

The results are very good with this type of configuration.

Thanks for your response.