450m/i installation standards

Good Morning all!

I am taking on the task of establishing minimum signal standards for installations. In my previous experience I had established a minimum signal of -72dBm, but that was in the ePMP realm and a different company.

I need to do 2 things to gain traction on this point. 1 is to establish a minimum signal strength. And 2 is to have good documentation as to why this was established, with accompanying info into the effects of poor signal on a sites overall performance. Any help would be greatly appreciated, and I would even be open to scheduling a meeting as we have a good size deployment of these in the field, and a stash of 450i’s that get deployed as needed to replace a different AP type as they fail.

Thank you,


Good morning Tim,

I think I can start the discussion here.

Minimum floor RSSI should be determined by your service levels you want to deliver to your customers. The short formula is this - all measurements are in dB, or dBm as indicated by ():

Noise floor of channel bandwith (dBm) + known interference (dB) + SNR required to provide your max service level (dB) + fade margin (dB) = RSSI floor at SM (dBm).

For example, using a 40 MHz channel, with 6 dB of known interference and you want 3 dB of added fade margin, supplying a 100Mb/s best effort service:

Noise floor = -97 dBm + SM noise figure (5dB) = -92 dBm
Known interference = 6dB
Fade margin = 3 dB
Service level = 100 Mb/s DL = 4x MIMO B modulation required = min 17 dB SNR

We add up the values and we see we require minimum -66 dBm to achieve 100 Mb/s DL throughput. Less throughput would be lower modulation level required, so lower minimum RSSI.

The next part of your question’ s answer is statistical. The net performance you can achieve on any particular sector is related to the weighted average of the SNR each SM in that sector is achieving. The easiest way to calculate this is to create a spreadsheet with each sector as a tab. Then in the columns, list the SM connected, the DL SNR reported and the volume of data passed through that SM in a 24 hour period, for example. Using the sumproduct function, you are going to take the average of the SNR reported, weighted by the 24 throughput. The actual formula is “=sumproduct(SNR, Throughtput array)/(throughtput column)”. There are quite a few excel tutorials on how to set this up.
cnMaestro can deliver a report, you edit the report in csv, create a pivot table to filter your data by sector, and run the weighted average. Sinple, yes? LOL. This is 20 years of radio network planning experience summed up in a few paragraphs.

The idea is this…an SM with low SNR, but passing a small amount of traffic has little effect on the sector. An SM with low SNR, and high throughput affects the sector in a more significant way, since the low SNR takes more time to handle the traffic, and therefore is a larger load on the sector.

My experience is that on most multipoint sectors where we have a range of SNR for the connected SM’s from 2x to 8x, the net throughput on the sector is between 50-70% of the spec of the AP. If you are dilligent about connecting SM above your minimum threshold, you can achieve 80-90% of the AP’s rating. A large part of being dilligent about your SM connections is making sure that your SM is connected to the best serving sector. If it connects to any other than the best serving sector, performance will take a hit. I’ve taken networks in the past that the SM was allowed to connect anywhere. By re-aligning SM’s to best serving sector, network net throughput increased by 30%.

I hope this helps. Please ask any questions you might have. I’m pretty sure the first question will be “what about the uplink?” This is a whole new discussion due to ATPC operation.



Thanks Dave. I have been putting some numbers into the capacity planner, and now I have more questions.

Here is an example of 1 that I am actively looking into.

What I am trying to figure out is what the actual forcasted capacity would be. Some folks pop up as N/A for the MU-MIMO and then come up at 1x. I hope to put a standard in place that is around 4-5x as a minimum. But I need to put data in front of my team to show just how detrimental the 1x and 2x connections really are.

SM’s that are modulating at 1x cannot participate in MU-MIMO, so the AP reverts to sector mode to communicate with them… this has a hugely negative effect on overall AP performance. Just a handful of 1x SM’s can drag an otherwise healthy AP to its knees. You want to avoid 1x SM’s at all costs and find a way to increase their modulation. But even some SM’s that have higher modulations might not be able to participate in MU-MIMO for various environmental reasons, like noise, reflections, nNLOS paths, etc. Again, those SM’s not able to participate in MU-MIMO will communicate with the AP in sector mode at whatever modulation they’re negotiating at. It’s important that you don’t have too many of these non-MU-MIMO participating SM’s on a PMP450m AP.

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Does this show anywhere in the interface? The drop from MU-MIMO to sector mode?

Or documentation that states that. Since we provide the AP, and our RSP’s hook up to it, i have to present pretty well documented info.

Yes, on the PMP450m AP, go to Tools → Link Status and you’ll see the columns marked SU-MIMO (that’s single user aka sector mode) and MU-MIMO (that’s multi user mode). SM’s that can’t participate reliably in MU-MIMO will be marked as NA aka not applicable.

You can find additional stats relating to modulation and MU-MIMO under Home → Session Status Tab → Power Tab.

That’s what throws me off. Some of them will show under both SU-MIMO and MU-MIMO even with the low modulation.

Maybe dumb it down for me a little bit lol. When a SM dumps part of an AP to sector mode, does this absorb a contention slot? I’m just trying to get all my ducks in a row to present this to my boss.

Experience wise, I know that installs below -72 really shouldn’t happen. I prefer to see -70 or better for all installs to allow for some fade. -60 to -65 for the faster packages is a must as well.

I’m not sure why your 1X-mimo-A’s are showing up as being supported in MU-MIMO groupings. What firmware revision is that AP running?

When the AP has to operate in SU-MIMO mode the SU-MIMO frame utilization will increase and it will have less air time to talk to the other SM’s using the more efficient MU-MIMO mode.

You can find your SU-MIMO and MU-MIMO frame utilization under Statistics → Frame Utilization.

When your SU-MIMO utilization reaches at or near 100% SM’s will start to have latency/jitter issues and at worse packet loss.

That one specifically is on

That’s a pretty old release at this point. You might want to move up to R22.1, especially if you’re using 3GHz/CBRS.

@Charlie do you know why @Tandr06’s 1X-mimo-A SM’s would be showing up as being eligible for MU-MIMO groupings? Is this possibly a reporting issue with the old firmware?

I do show the same on 22, not the one that came out in July but just before it.

The Rate isn’t the best place to know if SMs are eligible for MU-MIMO. Check the Statistics → Sounding Statistics page.

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Thank you Charlie,

If possible, do you have a sheet of dBm to MIMO rate for 5ghz? I’ve seen it posted for 3ghz, just not 5

1 other question for the group. In the capacity planner there is not option for Non Eligible. Would I just classify those as a 1 for use of the calculation?

You can find all that information and more in the PMP 450 series configuration guide located HERE.

Specifically, you’ll need to review Chapter 4: Reference information, on page 501.

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