MR46E - Too low 2,4 Ghz transmit power in ETSI ?

thomasthomsen
A model citizen

MR46E - Too low 2,4 Ghz transmit power in ETSI ?

I simply cant remember if I asked (and it is now turning into kind of an obsession for me 🙂 ).

Have anyone seen their MR46E set in ETSI reg. domain go above 12dbm in transmit power on 2,4 Ghz ?

Even with normal 3dbi antennas ? (MA-ANT-B6)

 

It (the MR46E) should be able to go to 17dbm with the 3 dbi antenna attached (that should give you a 20dbm EIRP that is the ETSI regulatory max), but it just stops at 12dbm 😕 (With the 3dbi gain in the antenna that is 15dbm EIRP - so we are basically missing 5dbm).

 

Created a case about it, but I never got a real answer. Just posts to documentation that did not make much sense, and talk about "remembering to add 3dbi because of beamforming" --- ehh ok .. that still leaves me with 2dbm that the radio should increase the transmit power with in the ETSI regulatory domain ?

 

To compare, I took a good old well tried out Cisco 2702E-E and attached the standard Cisco "rubber duck" to it.

Turned that up to the max allowed with that antenna, and walked around with my Ekahau Sidekick (passive scanning) to compare. (I also compared with some other Cisco APs that I had around, 2702i and 2802i and so on .. the result is almost the same). +/- 1db) - All APs where placed the same spot on the ceiling, at around 2.5 meters.

 

Here is a picture of the result on "the edge".

thomasthomsen_0-1652713167634.png

To no surprise Im missing around those 5dbm of signal strength.

 

Now my question. Why ? Why does the MR46E not turn up transmit power to more then 12dbm in ETSI ? (what crucial piece of information am I missing here ?)

Am I the only one who has a problem with this ? 🙂

 

 

Other Meraki AP does not seem to have this problem (when I take a quick overview of other Meraki APs that I have access to).

But the MR46E just does not go higher then 12dbm with the 3dbi antenna.

But .. at least its consistent - if I put the 3,8 dbi antenna on it (MA-ANT-A6), it turns down transmit power by one to 11 🙂

 

 

25 REPLIES 25
thomasthomsen
A model citizen

thomasthomsen_0-1652713979055.png

Just a snap of the data a little closer to the two APs.

Just a quick update and some explanation from Meraki on what might be going on here.

So, according to people I have been talking to there is an explanation (I dont like it, but here we go).

 

Because of beamforming, when using 4 antennas for beamforming, the AP will have to turn down transmit power 6db. (of it only had two antennas for beamforming it would be 3db).

 

- This is how the APs are certified today.

 

This makes somewhat sense, since the combined power output power of the signal cannot be higher then the 20dbm EIRP max in ETSI (Still only talking 2,4 Ghz here to keep it simple).

But why then do we still see such a weak signal when just doing passive survey, where beacons are single stream, and should then be send at the highest (or higher) transmit power (if configured).

 

- The explanation from Meraki is that, due to the fact that you cannot be sure that beamforming is working, and your client when roaming, normally listens for beacons, could "think" that the signal to a new AP would be ok (because of the max transmit power of beacons), but in reality the signal might not be (if beamforming is not working correctly).

And because of this, the entire AP turns down transmit power for everything.

 

- Now this opens up a whole new bag of worms, in my opinion.

 

What about those legacy a/b/g/n clients that do not support beamforming, and are only 1 SS.

In this case they will lose 6db of cell size. 😕 auch.

 

And furthermore if you do the EIRP calculation in this case there is still a problem (at least i think so).

12 dbm radio power + 6db for 4 SS beamforming + 3 dbi antenna gain = 21 dbm EIRP - Hmmm thats higher then the 20dbm max for ETSI.

So if what they say is the way they want it to work, the AP should turn down its radio to 11dbm in order to be compliant).

 

- Sorry if the above explanation is a bit messy 🙂 - But this is how I experience what they are telling me.

thomasthomsen_0-1654580417961.png

So this is a very rough drawing of how I understand whats going on. Black is the 1SS cell edge with ETSI max transmit power (that the AP does not do) - Blue is the potential celledge if / when beamforming is working (black and blue should be the same size here of course - but for illustrative purposes they are not 🙂 ) - Red is the actual signal strength cell edge , or if beamforming is not working.

And in case people do not realise how "much" 6db is in actual distance, it of course depends, but this illustration from semfionetworks illustrates it just fine (aka. half).

 

thomasthomsen_1-1654581573264.png

 

I'm trying to wrap my head around this how we should consider this in a design:

 

Let's say I design a VoWLAN network with every AP (MR46) at 14 dBm EIRP (@ 5Ghz). This means I set the AP in the dashboard at 8dBm (as far as I know that's always the AP output power without the antenna) and with the antenna gain I end up at 14dBm EIRP.

Does the beam forming gain only add up when I allow more output power than 14 dBm?This could result in sticky clients.

 

When beam forming kicks in does the output power of the AP go back to 2 dBm to compensate the 6 dBm gain to keep the max at 14 dBm?

 

I'd like to hear Meraki explaining this because if the behavior is unclear you can end up with pretty wonky designs.

 

The real problem is that not all clients supports beamforming.

(I mean, in Classic Cisco APs there where, as far as I remember, some proprietary beamforming tech that would give older clients without beamforming support a better signal, but I dont thinks that is around anymore - ClientLink was its name, now I remember - Introduced in 1142 APs , thats what my brain is telling me).

 

Standard based beamforming been around since 802.11n, but not all "n" clients supported it.

I think it is required to be supported on .ac and beyond.

But the client has to send "sounding" frames to the AP in order for it to work.

Now, if your client supports this, and the AP CAN actually use all 4 antennas for the beamforming, well then, in theory, you would get the added benefit of a 6db better signal.

For all clients that do not support this however, they will have to live with a much smaller cell size.

 

And that is my main issue with this.

 

There are so many unanswered questions here.

But Im pretty sure that the AP will not "go back", as you call it, (at least not the way it is now) in transmit power, because they already include that (perhaps possible) beamforming in their max EIRP setting at this time, no matter client support. But yeah. Its bad.

 

ww
Kind of a big deal
Kind of a big deal

For mr46 max is also 12 now . Looks like something has changed because it could go higher before.

KarstenI
Kind of a big deal

I just configured the RF-profile of my MR44 to min20, max30 and guess what ... 12dBm based on the dashboard output. Can't measure it as I am not onsite.

MarcelTempelman
Getting noticed

I have a customer with MR46E with MA-ANT-3F antennas and it's impossible to get the output power above 6dBm on UNII-1 and UNII-2e (max EIRP 17dBm instead of the expected max 23 dBm). It allows 12 dBm on UNII-2e channels.

 

On 2.4Ghz 3 dBm is the max output power.

 

Support could not give me an answer (like above) why the settings are lower than the MR42E (MR42Es do not have these limitations or uses the 3dBm margin, they are 3x3:3).


All in all the dashboard is a bit confusing when it comes to output power and EIRP values.

 

Edit : customer is in ETSI region also.

Just checking my case notes : my test on channel 100 (20mhz) saw the output power max out at 13dBm. The 3F gain is almost 11 dBm so 13+11=24 dBm which is 6 dBm below the regulatory 30 dBm. This makes sense if beamforming takes 6 dBm... (why isn't this in the datasheet ?).

I have also started to do some testing on 5Ghz.

UNII1 and 2 in ETSI - the EIRP max on 20Mhz channel on those channels is 23dbm.

AP with the "bendable" antenna 5,7 dbi gain, stops at 11dbm transmit power.

Thats 6 dbm lower then max. and that is ABSOLUTELY terrible ( for non-beamforming clients, bascially all pre. 802.11ax clients). Why is this AP only sending beacons ( that are 1SS transmissions) at the same lower power, regardless of beamforming. - And apparently also all other dataframes that are non-beamformed to these 1SS or pre-ax clients.  Should I start telling my customers not to deploy Meraki wireless in warehouses where pre. 802.11ax 1 SS clients are dominant ? (I mean 6db is half the distance, and on the cell edge, that is a lot of distance).

GIdenJoe
Kind of a big deal

Yeah I fell into this trap as well.  As I had a design with MA-ANT-3-F antennas even on the 5 GHz I had to use channels 100 and above to get to my normal transmit levels.  I did my survey with the assumption I could just use the antenna gain.

I don't understand why they did it per element for the indoor AP's while you can get huge distances with MA-ANT-27 on outdoor antennas without that per element definition.

I'm not even sure you are actually getting the extra 6 dB in combined antenna power to double your coverage distance.  I hope Meraki would come with a solution for this because you can have designs where you are only allowed to transmit 2 dBm on the 2.4 GHz band and 6 dBm on the UNII-1 band with that antenna... ridiculous actually!

In theory, beamforming to a client should give you a better signal at the client end. But that requires client "feedback", and in theory that was specified in the 802.11n specifications, but actually never implemented on clients (Intel, I think, might have done it, as the only client vendor at the time) , unless the Meraki APs can do what Cisco used to call "ClientLink(tm)", and I do not think they can.

Regardless, sending single stream data and beacons at the lower transmit power is bad, especially for warehouse environments. And Meraki should fix this, sooner rather then later.

DimuthuS
Here to help

If you have enabled Auto-rf this was a common issue with old firmware versions.

Increase the minimum transmit power to 17dBm and apply manually to all the APs.

You can keep the max tx power max or 20 dBm (AP supported max power on radios).  

I have tried setting the power manually but even then the dashboard keeps telling me the max output power is lower than expected. I haven't done any measurement tests to see if the measured output power increases when setting it manually higher. If so the dashboard is not reporting it right but considering the explanation that this is "working as designed" I doubt there will be any difference between the dashboard and the actual output power of the AP.

thomasthomsen
A model citizen

Just because Im an annoying fellow (I tried to write a bad word here, but it would not let me 🙂 ) , I created this easy visualised sheet that tells you how bad this really is.

From all the APs I had access to. (I do have an ... ehhh ..  collection of Cisco Classic APs as well, but I just compared to the "new ones").

https://docs.google.com/spreadsheets/d/1-s5IOMg09DTCFnODNapsYXta_onfO4W6SqG3E6sn9tg/edit?usp=sharing

(I want to in advance apologize for the sarcastic and Im guessing for some, un-fun, notes I made in it).

I also did real world measurements, standard passive scanning for beacons, and it fits the data. 

I might create one for 5Ghz just for fun. One for UNII1 and one for UNII2-EXT.

GIdenJoe
Kind of a big deal

So @thomasthomsen you used the values the dashboard GUI gave you to input into the excel document?

Wow those indeed are very inconsistent especially when they actually know the value.

 

I did also find that using an MR76 with MA-ANT-27 gives better results than an MR46E with MA-ANT-3-F just because of the per element thing...

This should not have anything to do with elements (Im a little unsure what you mean here ... 🙂 )

But you are right, the MR76 would do better , raw signal wise, in every scenario (read, antenna attachment).

They should just be able to beacon, and potentially do single stream data, at the highest allowed EIRP in your reg. domain. And they do not. But the MR46E is the worst one.

(If I needed it to for some strange design reason...... it is of course not "best practice" to have your wireless network at max power - EIRP)

With per element I mean like on the datasheet.
So the antenna gain on the MA-ANT-27 datasheet is the actual antenna gain so you can configure up to the EIRP minus that gain.
However with the MA-ANT-3x series they went for a per-element dBi gain which means you need to add the per element gain too.  So a 4x4 AP like an MR46E supposedly adds another 6 dBi gain which lowers your max Tx power again.  A 3x3 AP would add about 4.5 dBi on top of the regular antenna gain.

 

As max power goes as you know max power is bad practice towards end devices if you are talking about a Tx power of around 20 dBm or higher since endpoints usually can't transmit more than 14 dBm back.  However with these large antenna gains max power is already much lower, even lower than 14 dBm so that negates any end device upstream issues.

cmr
Kind of a big deal
Kind of a big deal

We have one MR46E and it looks like I get the same 2.4GHz results in the UK to what you see, but on the 5GHz it looks like I get 19.9db (15+4.9) which looks better, unless I am supposed to see more here?

 

cmr_0-1660170660218.png

cmr_1-1660170712244.png

cmr_2-1660170891549.png

 

 

 

Well here you are on channel 56 - UNII2A.

Regdomain says 200mW EIRP on a 20Mhz channel at this frequency - so that would be 23dm EIRP.

(Channel 36 <-> 64 are here).

So here you are potentially missing 3.1 db. (And that's the same amount as you are missing with the same antenna on 2,4Ghz).

 

100 <-> 144 UNII2-EXT you are allowed 1 Watt EIRP for a 20Mhz channel = 30dbm EIRP.

 

And remember, If you increase your channel width the AP must decrease transmit power 3db when its twice as wide.

So 3 db down for a 40Mhz channel, and another 3db down from 40Mhz if you go to 80Mhz.

 

PS: The rules are a bit more "complex" in 5Ghz frequency range 🙂 - When you factor in TPC + there are different rules for different parts of the range. - But Im pretty sure the APs supports TPC.

 

PPS: Perhaps I should mention the above numbers are for ETSI reg domain. What US and other domains are doing I would have to look up 🙂 - Im sure there is a WiKi page for it 🙂

 

I'm a bit puzzled about this:

Quote: And remember, If you increase your channel width the AP must decrease transmit power 3db when its twice as wide.

So 3 db down for a 40Mhz channel, and another 3db down from 40Mhz if you go to 80Mhz.
End Quote
As far as I know you don't decrease your Tx power.  The only thing that does happen if you double your channel width is that you lose 3dB in SNR which could lower your MCS index.

Well , those are the "rules" of our local regulatory domain (and I think it's the same for the rest of ETSI).

- It states something like (in shortened form) --- You can use 10mW/mhz up to a max of 200mW EIRP (in UNII1-2A).

 

Basically means that using a 20Mhz channel I can have a 200mW EIRP (10x20=200).

But if i go to 40Mhz the radio needs to turn down its transmit power to 5mw/mhz in order to stay at the max allowed 200mW EIRP (40x5=200) ... and so on.

 

In UNII2C my local regulatory states 50mW/Mhz and a max EIRP for 1000mW (1Watt).

 

But yeah .. you also get the 3db SNR thing ... but that happens regardless.

Hi Cmr,

By looking at your screen capture you shared, you have set to your minimum and maximum power settings for the radios 5dbm and 30dbm range for the auto rf. so the target power keep 12dBm. If you want increase the power you have to decide what is the best power APs can operate without any coverage holes. I would be increase the minimum power value from 5 dBm to 15dBm, if you want to see 15 dBm target power.

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