Understanding RF Performance Table for Meraki MR

SOLVED
klausengelmann
Here to help

Understanding RF Performance Table for Meraki MR

Hello Meraki Community.

 

Please, I need some help to understand the "RF Performance Table" inside Meraki MR Datasheets.

Here is an example:

 

MR36 Datasheet - Cisco Meraki

 

klausengelmann_0-1623588748319.png

If I understand correctly the "RF Performance Table" is indicating the conditions where the Data Rates will be achived.

 

For example, in order to achive MCS9 Data Rate it is necessary both conditions:

1) The MR transmission power should be 13.5 dBm.

2) The end-user RX Sensitivity (like RSSI) should be -67 dBm.

 

Is this correct ?

What I am struggling to understand is: what will happen if you use lower power levels (TX Power) on the AP?

I am asking this because the table is showing power levels greater than 12 dBm.

 

Regards,

1 ACCEPTED SOLUTION

Accepted Solutions
Bruce
Kind of a big deal

Re: Understanding RF Performance Table for Meraki MR

My understanding is that the TX Power (conducted) is the maximum power that can be sent to the antennas for that data rate - the actual emitted power may vary slightly based on the radiation pattern of the antenna. And the receive sensitivity is the absolute lowest signal strength at which the access point can receive a signal to meet that data rate.

 

Other factors can also play into this, especially the receive sensitivity. For a quality signal you also need a good signal to noise ration (SNR), so if your noise floor is too high then you won’t meet the expected data rates anyway. You also need to remember that just because your AP can transmit at, one power level, it doesn’t necessarily mean the client can achieve the same power levels to send its signal back.

 

it’s also worth noting that depending on your region and the regulatory authority for radio frequency use there may also be software restrictions enforced on the device to ensure it is compliant with local laws.

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4 REPLIES 4
Bruce
Kind of a big deal

Re: Understanding RF Performance Table for Meraki MR

My understanding is that the TX Power (conducted) is the maximum power that can be sent to the antennas for that data rate - the actual emitted power may vary slightly based on the radiation pattern of the antenna. And the receive sensitivity is the absolute lowest signal strength at which the access point can receive a signal to meet that data rate.

 

Other factors can also play into this, especially the receive sensitivity. For a quality signal you also need a good signal to noise ration (SNR), so if your noise floor is too high then you won’t meet the expected data rates anyway. You also need to remember that just because your AP can transmit at, one power level, it doesn’t necessarily mean the client can achieve the same power levels to send its signal back.

 

it’s also worth noting that depending on your region and the regulatory authority for radio frequency use there may also be software restrictions enforced on the device to ensure it is compliant with local laws.

View solution in original post

GIdenJoe
Kind of a big deal

Re: Understanding RF Performance Table for Meraki MR

To add what Bruce said:

The table shown only speaks if the transmission is done in 5GHz in VHT40 which means a 40 MHz wide channel in 802.11ac mode.

 

The Tx power conducted (like Bruce said) is the max power the radio can transmit in MCS 9 in VHT40.
and the RX sensitivity is NOT the clientside but the other way around.  So if the client would send a frame in VHT40 at MCS9 towards the AP, the AP needs to receive that signal at at least -67 to succesfully decode that frame.  And yes other factors like noise also influence this, but with a low enough noise floor the signal needs to be at least received at -67 at the radio!

So it can be received at the antenna at a bit lower and the antenna gain will add a bit to the signal again. 😉

klausengelmann
Here to help

Re: Understanding RF Performance Table for Meraki MR

Hello Bruce and GIdenJoe.

 

Many thanks for your reply and explanations !

 

Now I understand a lot better the "RF Performance Table".

 

In fact, the "RX Sensitivity" is easier to understand: if the AP receives a frame with a value lower than -67 dBm it is unlikely to achive MCS9 for VHT40.

 

My mind plays a trick on me when I consider the "TX Power Conducted" because I see all the values and they are always higher than 10 dBm.

 

Then I am trapped thinking about an MR36 using 5 dBm as the transmit power. Looking at the table I cannot guess which Data Rate could be achieved.

 

This is the point where I am still confused when reading the table. Of course I did live captures and see MCS rates with power levels lower than 10 dBm.

 

Regards,

Bruce
Kind of a big deal

Re: Understanding RF Performance Table for Meraki MR

Glad it helped. With regards to the TX Power, this is just the maximum the AP can use for that MCS, it doesn’t mean it will (or has) to use it. If you have multiple APs in the environment the Meraki cloud will adjust their power levels to reduce the interference between APs while still maintaining good service to the clients. 

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