Distance best practices & performance based on subscriptors

Hi all! I’m deploying a WISP network using ePMP 3000 with RF elements antennas (2 x 90 degrees). My plan is to connect my subscriptors to distances up-to 3 KM max per tower.

I would like to get your recommendation based on your experience on the following topics:

  1. I’m planning to use Force 130 and Force 300-13L subscriptors. How will the Force 130 affects the performance of the network if any? Is there any problem if I mix both kind of subscriptors?

  2. I’ve heard that the performance of the AP is equal to the performance of the weakest subscriptor, is that right? If so, which parameters should I look in order to identify if a subscriptor isn’t performing well (SNR, Bandwidth?)?


Why are you wanting to use 2 x 90deg antennas? I’d recommend you use Cambium’s OEM antenna for best MU-MIMO performance.

  1. I’d avoid the force 130 and stick to AC based radios, like the Force 300. You’ll want AC radios for best performance for highest modulation (upto 256QAM) and MU-MIMO. F130 and other N based radios cannot participate in MU-MIMO.

  2. Cambium has some secret sauce in their scheduler called “airtime fairness” that helps prevent clients with bad modulation from disrupting the entire AP. That being said, to ensure best overall performance, you’ll want to make sure that all of your clients are installed with good RSSI and SnR levels.

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It was just the recommendation I got after a lot of research, I will try those for few months (I already bought them) and I will switch to Cambium OEM antennas if needed, thanks for the tip! (This is my first tower and I’m pretty sure I will learn a lot of things along the way).

For point 1) Ok, I have purchased just few Force 130 for testing, so I still have the chance to go for AC based radios. Which is the cheapest AC subscriber available?

For point 2) Good to know Cambium has an “airtime fairness” protection mechanism! But still I will monitor the RSSI and SnR per your recommendation.

You can use the F130’s, and mix them with AC clients as well… but if your goal is maximum density and performance, then you’ll want to use all AC clients. Only AC clients will participate in MU-MIMO with upto 256QAM.

I’d hit up your Cambium regional sales manager aka RSM to find out what AC models are available in your region along with pricing.

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3km is kind of short for the epmp system, but this also depends on your subscriber density and object density.

What matters the most is to set the max distance in the all APs the same. This is important for if you add another tower close enough you can interfere with yourself and also make sure everything has a good timing reference, eg packetflux cambium sync with a syncbox jr or a cmm5. Ugps does work but only supports one inline AP, so you would need one per AP.

As Eric said only AC radios will participate in Mu-MiMo but the N based radios will work and you will not see any major degredation on the sector for mixing SM types. Suggestion: get a e1k e1k-lite if you only have 10 or less f130s) or e2k AP and overlay on a different frequency (same distance settings though) to make the N based SMs (your low budget clients) use it instead of the e3k AP. This will give you more available bandwidth for the sector and improve serviceability.

Since you are using two kp 90 sectors, make sure you horizontally space your antennas about 4ft (more is better) and aim them in a parallel direction for Mu-MiMo to work. The KP antennas are very good (we use them a lot) but they do not yet have a quad port sector that is usable.

He said RF-Elements not KP so I’m assuming Horns (no lobes to speak of).
Also he said 2x90° (so 180°?) and the OEM sector is only… what 70° (if you’re being generous) ?

Agree with avoiding N and sticking with AC.

One of the biggest advantages ePMP had over Ubiquiti back in the day (other than GPS) was “airtime fairness”. It’s very nice when a single bad link can’t bring the whole AP to a crawl.

Is airtime fairness “back” in 3k? I recall it not being there initially.

Keep in mind that the OEM 3000 Sector is only 70° and just barely at that. It’s a really good sector otherwise though we have several deployed and more to to go. We are also big fans of the RF-Elements asymmetrical horns though too and right now if you need 90° with a 3000 two RF-Elements 45° Asyms would do it (you have to point them so that they do not overlap, so two 45s would give you 90, two 90s would give 180°). See this post ePMP 3000 with RF Elements Horn - #10 by Dmitry_Moiseev

While 3k may be a short distance for most radios that may not be the case for the little 14 and 13db radios. It will also depend a lot on what frequencies you use and what the power limits are in your regulatory domain. I have no personal experience with the 300-13’s other than a few we used for very very short (shooting across a 200ft parking lot kind of thing) PTP links. No idea how well they would work at 3km PMP, we don’t use anything below F300-16 for customers and those are all around maybe 2km but usually much less. The 300-19’s we run up to maybe 4km or so and pretty much F300-25 for everything up to 10km.

While you can mix and match N and AC on ePMP I wouldn’t if I could avoid it. While technically there shouldn’t be any problems they have repeatedly introduced, fixed, re-introduced, fixed, changed, fixed, re-introduced a whole host of firmware bugs that cause problems specific to AP’s with mixed clients on it. Also as pointed out, N can’t do MU

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I thought it was QoS they broke ? Airtime fairness being broke though would explain things also.

Yep, it was there supposedly from the beginning and was confirmed by Cambium staff in THIS thread.

Maybe we should start a different thread discussing this as I’d like to hear why you think airtime fairness is broken.

I didn’t , I thought QoS was broke, it’s Jacob_Turner said he thought it was broke or missing or whatever.