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RF-enviroment - how and why and what?

I'd like to know more about how to interpet the result of an RF-enviroment mesarument.

Is there any articles I can read or is someone so nice to tell me how do optimize my network. 


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Re: RF-enviroment - how and why and what?

[ Edited ]

I will start with Part 1 

 

APs and clients transmit data from one location to another in form of electromagnetic waves.

These waves operate at different frequencies. Frequency is measured in Herz.

When a wave travels it takes a signal loss due to a phenomenon called Free Space Path Loss.

Lower frequencies have longer wavelength and travel further then higher frequencies.

Of course obstacles do further weaken the wireless signal. 2.4GHz travels further then a 5GHz wave and will get more easily through an obstacle.

2.4GHz APs have a longer history then 5GHz capable APs. The problem is, that in most places the 2.4GHz spectrum has become overcrowded with competing APs (neighbours AP, Bluetooth, Baby monitors. Wireless Headphones, etc.)

All these devices using the same frequency range from 2400 MHz to 2483 MHz can causes saturation.

Speaking of saturation look at a this post I made:

http://community.ubnt.com/t5/UniFi-Wireless/FYI-Wireless-2-4GHz-Headphones/m-p/1641432#M175508

 

5GHz gives you much more flexibility. It offers more non overlapping channels to choose from than the 2,4 spectrum. Mind that the amount of available channels for 5GHz depends on the region you  live in.

Because 5GHz propagates less further then 2,4GHz and has more available channels it is the spectrum to choose for a high density situation. Where many clients have to be serviced in a small area.

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Re: RF-enviroment - how and why and what?

+1
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Re: RF-enviroment - how and why and what?

[ Edited ]

I will start with Part 1 

 

APs and clients transmit data from one location to another in form of electromagnetic waves.

These waves operate at different frequencies. Frequency is measured in Herz.

When a wave travels it takes a signal loss due to a phenomenon called Free Space Path Loss.

Lower frequencies have longer wavelength and travel further then higher frequencies.

Of course obstacles do further weaken the wireless signal. 2.4GHz travels further then a 5GHz wave and will get more easily through an obstacle.

2.4GHz APs have a longer history then 5GHz capable APs. The problem is, that in most places the 2.4GHz spectrum has become overcrowded with competing APs (neighbours AP, Bluetooth, Baby monitors. Wireless Headphones, etc.)

All these devices using the same frequency range from 2400 MHz to 2483 MHz can causes saturation.

Speaking of saturation look at a this post I made:

http://community.ubnt.com/t5/UniFi-Wireless/FYI-Wireless-2-4GHz-Headphones/m-p/1641432#M175508

 

5GHz gives you much more flexibility. It offers more non overlapping channels to choose from than the 2,4 spectrum. Mind that the amount of available channels for 5GHz depends on the region you  live in.

Because 5GHz propagates less further then 2,4GHz and has more available channels it is the spectrum to choose for a high density situation. Where many clients have to be serviced in a small area.

Please give kudo's to the people who have helped you and mark your thread as solved when you receive a solution to your issue.
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Re: RF-enviroment - how and why and what?

[ Edited ]

Part 2

 

To avoid interference and maximizing performance of WiFi it is crucial to undestand how channels operate.

In radio communication an AP gets a channel and bandwidth assignment over which it transmits and receives signals from clients. This channel assignment pertains to the center frequency of the first 20MHz used by the station.

"Latest" technologies use channel bonding, this permits to use larger channel bandwith for "higher" throughput.

Unifi defines that with HT20, HT40 and HT80 (20, 40 and 80MHz). Higher width means more throughput, but watch out, the draw back is that this uses more available radio spectrum. And you'll have less clean channels to use for additional APs. And the wider you run your AP the power has to be spread across a wider channel. This results into shorter range.

For 2.4GHz it's recommended to use HT20 with channels 1, 6 and 11. HT40 and HT80 are best used with 5GHz.

It's important to know your environment, you should use channels that are free of utilization by other radios.

Place neighboring APs on non adjecent channels.

Use a WiFi scanner to see neighboring APs and what channels they use. Also use the ability of the latest unifi AC APs to do an RF-Environment scan. This scan will show you also radios that a "normal" WiFi scanner won't see.

It scans the complete spectrum and shows the utilization for each available channel and channel with. Again let me point you to my Headphone example. http://community.ubnt.com/t5/UniFi-Wireless/FYI-Wireless-2-4GHz-Headphones/m-p/1641432#M175508

No Wi-Fi scanner would have shown that the upper third of the spectrum is occupied by a Headphone.

Imagine you install your AP and use channels in that high utilzation range. You would have very low throughput and you wouln't know why!

 

 

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Re: RF-enviroment - how and why and what?

@osunifi: thanks for sharing your experiences!

 

Although I have noticed some noise on channel 112 on the RF scan on all my three AC PROs I had left the AP in the garage on channel 100 and 80 Mhz (which crosses channel 112) until I read your latest post.

 

Its now on channel 116 where its silent.

 

image.jpeg

 

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Re: RF-enviroment - how and why and what?

Part 3

 

Now I'd like to explain why it is important to use a clean channel. Why is it best that just your AP uses a channel with lowe noise and just by itself.

 

There are two reason, one is noise. Imagine you're in a packt bar with lots of people and you're trying to talk to a friend 6 feet away. But you're not allowd to shout. You're only allowed to talk with a defined max loudness.

The more noise there is, like more people (not clear defined communication on your channel) the less you'll understand and you have to repeat your words until your friend understands you.

 

The second reason is a clear defined communication from a neigboring RF source talking on your channel.

To understand this one needs to know how talking to each other is regulated in the 802.11 standard.

It is based on CSMA/CA Carrier Sense Multiple Access/Collision Avoidence Protocol. A 802.11 station will listen to the wireless channel prior to transmit data. If the channel is available then the station will transmit. If the channel is occupied the station will wait a random time until it listens again. This is done to avoid that two stations transmit at the same time. Te receiver would experience a collision and data would have to be retransmitted.

The more stations you have the more likely a collision is to occure.

 

Also an optional protocol is the RTS/CTS Request To Send/Clear To Send. I think that says it all what it does. the station asks if it can send now data. The AP tells all the clients to shut up for an amount of time. And sends the requester Clear To Send for that amount of time.

 

All of the above is a so called Collison Domain. Now since the carrier is a RF signal and has a defined channel. It could be that your AP hears on the same channel many other stations that are not part of your SSID. And this will make you Collision Domain much larger more stations, more waiting and more collisions = slower throughput.

 

So please be patient with me you RF specialists that might read this. I tried to make this not to technical and readable and english is not my main language.

If I screwd up somewhere let me know and I'll edit the my posts.

 

 

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Re: RF-enviroment - how and why and what?

The above is great. Now can we have Part 4: what to do when faced with sub optimal conditions not under your control?
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Re: RF-enviroment - how and why and what?

[ Edited ]

 


phk46 wrote:
The above is great. Now can we have Part 4: what to do when faced with sub optimal conditions not under your control? 


Well let me try part 4 then...

 

The most basic thing you'll find on the forum when someone complains about performance issues is the suggestion to change channel. By reading part 3 it should be clear that a channel just for yourself is the best you can get.

 

-If you have a unifi AC AP first thing to do is an RF-Environment scan. It will show you what is the best channel for you to use. It will show you where is the least noise and where the least utilization is. That's where you want to put your channel.

-Don't shoot yourself and into your neighbours foot by using High Tx. If you just have one AP your "fine", you're just shooting your neighbour. But if you use more then 1 AP you might interfere with your own APs. Because even if you use a different "non overlapping" channel on your second AP you still have overlap.

Check out this picture.

3-channel-wifi-arrangement.jpg

picture taken from: http://www.wirelesswaffle.com/?entry=entry130212-072406

 

So try to use non adjcent channels to reduce interference and use only as much TX power as needed.

Here comes 5GHz into play. Since it travels only about half the distance of 2.4GHz that should be the spectrum of choice if you're in trouble.

You neighbours will pollute you less and it's same if you have more then one AP yourself.

 

I've never mentioned SNR Signal to Noise Ratio. That's the single most important factor for performance (beside the channel width of course). This is what determines at what connection speed your clients gets connected to the AP. The better that ratio the more speed you get. But now be careful. "Let me increase TX Power to the Max to get a better ratio". Don't forget that you could be shooting yourself in the foot doing so...

What can you do to better that ratio without shooting into your foot?

AP placement, the closer you get to your clients the better SNR you have. Or the further away you get from your neighbour... ;-)

Or get yourself a good ol' ethernet cable... 1Gbps ALWAYS ANYTIME!! (sorry now phones and tablets... LOL)

 

 

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Re: RF-enviroment - how and why and what?

So channel 1 and 6, 6 and 11 are disturbing each other?

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Re: RF-enviroment - how and why and what?


@colbru wrote:

So channel 1 and 6, 6 and 11 are disturbing each other?


If you are using HT40, yes - they will overlap.  Channel 6 will overlap both 1 AND 11 - really not good 


IF you are using HT20 channel width, then no - they are clear from each other.

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Re: RF-enviroment - how and why and what?

[ Edited ]

Well there is the so called sideband lobe around the carrier fequency.

At HT20 the carriers are not getting in each others way, so they do not take part in the same Collision Domain.

But the sideband lobe creates the noise that we don't want. Because it lowers the SNR.

The noise is clearly seen on the picture below.

 

superg_ntk_athos_11g_1_6_11.gif

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Re: RF-enviroment - how and why and what?

This is a great intro to Wi-FI.  THANK YOU.  I've only had my UniFi for three days and this helps.

 

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Re: RF-enviroment - how and why and what?

Welcome to the best community on the planet. Incrediblely helpful and spares nothing to help you.

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Re: RF-enviroment - how and why and what?

What tool is that?

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Re: RF-enviroment - how and why and what?

That's from a Spectrum Analyzer.

Pic taken from here:

http://www.tomsguide.com/us/atheros-super,review-202-4.html

 

Here a good webinar regarding spectrum analysis. Very useful!

http://www.metageek.com/training/webinars/view/visual-spectrum-web.html 

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Re: RF-enviroment - how and why and what?

Thank you, very useful information. I'll use this in my blog.

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Re: RF-enviroment - how and why and what?

Thanks for the information and I understand the examples provided. 

 

My question is.....

 

By doing the RF scan - then having the Channels on the AP's set to AUTO. Will the APs automatically select the least saturated channels?

 

Or is the purpose of the RF Scan to run the scan - then use the results to manually edit each AP and select the least used Channel?

 

 

Basically - should I just leave the controller alone to do it's thing - or is manual intervention required to ensure effencies with the channels?

 

Thanks in advance

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Re: RF-enviroment - how and why and what?

"... Or is the purpose of the RF Scan to run the scan - then use the results to manually edit each AP and select the least used Channel? ..."

 

Manual, manual, manual!  Auto = Auto and certain headaches.

 

As noted before:

 

Select least used channels: 2G only 1, 6 and 11 @ HT20.  5G - Try to use non DFS channels first @ VHT40.  Depending on your AP density use VHT80.  The wider the bandwidth gives higher throughput, however, it makes it harder to reuse the frequencies.  Once you set the channels, perform another scan on all APs to confirm set up.  

 

Never "Auto", not yet anyway.

 

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Re: RF-enviroment - how and why and what?


@f1resteel wrote:

By doing the RF scan - then having the Channels on the AP's set to AUTO. Will the APs automatically select the least saturated channels?


 Nope.  Auto means when the AP powers up it does a quick scan and picks the best channel at that time, then it stays there until the AP resets again.

 

Manually pick your channels - it's much more predictable and less likely to change if the AP reboots and decides to pick a channel that's OK then but not later.

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Re: RF-enviroment - how and why and what?

Hi

 

I came to the forum to ask some questions. saw this thread, thanks to  osunifi 

 

 

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