Distance between Root AP and Mesh AP - Signalstrength

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Distance between Root AP and Mesh AP - Signalstrength

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Distance between Root AP and Mesh AP - Signalstrength
Distance between Root AP and Mesh AP - Signalstrength
2020-05-20 19:32:36 - last edited 2020-05-25 01:38:27
Model: EAP225-Outdoor  
Hardware Version:
Firmware Version:

Hi are there any recommendations for the distance between two APs in a mesh system based on their signal strength ?

 

What would be the minimum signal strength of the Root AP at the position of the mesh AP to have a quality connection between both? -65dbm or less ? Or how strong should be the signal at the overlapping point? -50dbm to allow a good data transfer?
 

Are there any planing tools available? 
 

I just got a Eap225-Outdoor for testing and I am trying to figure out how many I need.

 

Thanks for your help.

 

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Re:Distance between Root AP and Mesh AP - Signalstrength-Solution
2020-05-21 12:09:04 - last edited 2020-05-25 01:38:27

@Lens, a RSSI of -50dBm (100%) is unrealistic for larger distances.

 

Let -50dBm (and higher) equal to 100% signal quality and -100dBm equal to 0% signal quality, then you would need at least 45% signal quality for a reliable link, albeit with 35-40% quality some services with small bandwidth requirements still could work.

 

The commonly used formula is: signal quality in percent = 2 × ((RSSI in dBm) + 100)

 

This is what you can expect:

 

-50dBm (100% signal quality) would be »Very good«, but can be achieved over very short distances only.
-69dBm (62% signal quality) would still be »Very good«.
-70dBm is »Okay« (60% signal quality), it's the minimum RSSI value which ensures reliable packet delivery.
-80dBm is »Not good« (40% signal quality), packet loss can appear.
-90dBm is »Unusable« (20% signal quality), approaching or drowning the noise floor.

 

So, with -61dBm RSSI you have a signal quality of 78%. That's pretty good for reliable data transmissions.

 

 

BTW: You also need to take SNR (signal-to-noise ratio) into account. Quality for data transmissions depends on SNR, not the RSSI alone.

SNR is calculated as follows: SNR in dB = RSSI in dBm − Noise Level in dBm

 

So, with a RSSI of -61dBm and a noise level of -98dBm the SNR is 37dB, which is pretty good.

 

For reliable data transfers you need a SNR of 25dB or better.

 

 

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Re:Distance between Root AP and Mesh AP - Signalstrength
2020-05-21 02:23:42

 

Lens wrote

Hi are there any recommendations for the distance between two APs in a mesh system based on their signal strength ?

 

What would be the minimum signal strength of the Root AP at the position of the mesh AP to have a quality connection between both? -65dbm or less ? Or how strong should be the signal at the overlapping point? -50dbm to allow a good data transfer?
 

Are there any planing tools available? 
 

I just got a Eap225-Outdoor for testing and I am trying to figure out how many I need.

 

Thanks for your help.

 

@Lens 

 

According to the test result, the recommended distance between root AP and mesh AP is less than 180 meters.

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Re:Distance between Root AP and Mesh AP - Signalstrength
2020-05-21 09:15:55

@jonas thanks. Is there no recommendation with the signal strength? I measured the eap225-outdoor performance and at about 25m signal drops to about -61dbm. So if I put the second eap at 50m of each other, the signal overlap would be around -60dbm. Is that good enough for a speedy data transmission between the two eaps or do I need an overlap of -55dbm for example.

 

Thanks Lens.

 

 

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Re:Distance between Root AP and Mesh AP - Signalstrength-Solution
2020-05-21 12:09:04 - last edited 2020-05-25 01:38:27

@Lens, a RSSI of -50dBm (100%) is unrealistic for larger distances.

 

Let -50dBm (and higher) equal to 100% signal quality and -100dBm equal to 0% signal quality, then you would need at least 45% signal quality for a reliable link, albeit with 35-40% quality some services with small bandwidth requirements still could work.

 

The commonly used formula is: signal quality in percent = 2 × ((RSSI in dBm) + 100)

 

This is what you can expect:

 

-50dBm (100% signal quality) would be »Very good«, but can be achieved over very short distances only.
-69dBm (62% signal quality) would still be »Very good«.
-70dBm is »Okay« (60% signal quality), it's the minimum RSSI value which ensures reliable packet delivery.
-80dBm is »Not good« (40% signal quality), packet loss can appear.
-90dBm is »Unusable« (20% signal quality), approaching or drowning the noise floor.

 

So, with -61dBm RSSI you have a signal quality of 78%. That's pretty good for reliable data transmissions.

 

 

BTW: You also need to take SNR (signal-to-noise ratio) into account. Quality for data transmissions depends on SNR, not the RSSI alone.

SNR is calculated as follows: SNR in dB = RSSI in dBm − Noise Level in dBm

 

So, with a RSSI of -61dBm and a noise level of -98dBm the SNR is 37dB, which is pretty good.

 

For reliable data transfers you need a SNR of 25dB or better.

 

 

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Re:Distance between Root AP and Mesh AP - Signalstrength
2020-05-21 15:50:18

Thanks that helped me a lot. I only have to cover about 40m around a C-shaped building so I will put one Eap on every end of the C so I should be well covered in the center of the C and also around the corners. Tried the one eap I have in the center of the building but the signal is not that good around the corners then.

 

 

One question about the signal quality. Netspot indicates a quality of 59% with -41dbm and -92dbm of noise, is it the same quality you are talking about?

 

 

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Re:Distance between Root AP and Mesh AP - Signalstrength
2020-05-23 08:39:06 - last edited 2020-05-23 08:50:42

 

Lens wrote

One question about the signal quality. Netspot indicates a quality of 59% with -41dbm and -92dbm of noise, is it the same quality you are talking about?

 

I don't see »Signal Quality« (sometimes called »CCQ« = »Client Connect Quality«) in NetSpot. NetSpot reports »Signal Strength« as a percentage (where -100dBm = 0% and -0dBm = 100%) and also »Noise Level« as a percentage. This means a 100% signal quality can never be reached as well as a 50% noise level is almost unlikely to appear in reality. 

 

NetSpot indeed knows about the common formula for computing »Signal Quality/CCQ«, but their analyzer software doesn't display this value.

See their post about RSSI mentioning the SQ/CCQ formula: https://www.netspotapp.com/what-is-rssi-level.html

 

In my opinion the NetSpot statistics should better show SQ/CCQ rather than »Signal Strengh« as a percentage.

At least they show the SNR as a colored bar under »Level«, which gives a good overview of quality, too.

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