WiFi congestion/collisions?


Has anybody experienced WiFi slowness due to congestion/collisions?

As I was troubleshooting my RPi WiFi problem yesterday, I downloaded a Windows freeware to check the WiFi ‘landscape’. I was surprised to see that most of the neighbor’s wireless routers are using channel 6. That can’t be good. Is channel 6 the router’s default? I don’t think we all configured the same channel. I changed mine to an unused one now. Let’s see if it makes any difference.


On 2.4Ghz (802.11B/G) there are only 3 non-overlapping channels.1,6,11 I believe.
N uses more.
I have dozens of WAPs in my area.
I have moved everything that can use 5Ghz to 5Ghz.Only Sense, nest and an old laptop use 2.4Ghz.
I think most of the channels are non-overlapping, however, it depends how wide the channels are.
5Ghz (802.11a) does have less range but can provide a lot more performance in congested areas.


Interesting. The other 2 or 3 routers that are not using channel 6, are using channels 1 and 11.

I set mine to channel 8 now.


Best bet is to go to 1 or 11 also.

On channel 8 the the channel 6 wifis are still going to be in your way.

Also sometimes they use “double bandwidth” settings which means they may nominally use channel 6 but actually use 6 and 11 or something.

I guess just try :slight_smile:

Also the rpi3b+ wifi antenna seems to be highly anisotropic to me.
So turning the Raspi may help if that’s an option.


I will move my router to channel 1. If I remember correctly, there was only one other router on that channel. The signal was also very weak, denoting, maybe, distance from me.



Some WIFI devices will automatically choose the channel with the least use.
I have 4 WAPs in my small house because I need the coverage and get a lot of interference.
My brother has a larger house but has less interference and gets away with only one WAP.


My router was set to auto (default), and still picked the busiest channel (6). I unchecked auto.

My PC is connected to the router using ethernet, but the family uses WiFi, and complains from time to time about slowness.


If you have a smartphone download https://play.google.com/store/apps/details?id=com.vrem.wifianalyzer
Will detect the bonded channels too (20, 40, 80 MHz)… as used in N, AC.
PS: This one makes better graphs, but gives no info on bonded channels: https://play.google.com/store/apps/details?id=com.farproc.wifi.analyzer&hl=en_US


I have the other Wifi Analyzer on my phone (top right), not this OpenSource one.

I don’t use the phone very often, hence the Windows download.:wink:


I had to move my router 5-6 feet closer to my Pi (different rooms), because I was having 12% packet losses, as reported by the MLAT.

And yes, the 2.4GHz band sucks, I have everything possible on the 5GHz. Unfortunately, the cellphone companies are eying that band too, because it is “free”:


I experienced that problem regularly because I was using only 50% of the router’s output power. I increased it to 70%, and the problem went away.

Why did I reduce the power in the first place, you ask? I don’t know for sure, but after 2 wireless routers, in a row, having no WiFi output after a short time, I decided to reduce the power, and since then no router failure.


If you reduce the router power, the other end will increase the TX power to “compensate” for what it sees as a weak channel link.
Maybe that’s why you burned the WiFi in the Pi.

I keep all my routers at 100%. None “burned”.


Very good point. I’ll keep this in mind for future reference. One of the other two RPis is very old, and farther away.


If your family complains about slow wifi get 5 GHz.

Not as good through walls but still can take a lot of traffic of your 2.4 GHz part of the network.
Most modern smartphones also have 5 GHz.

I gave mine a different name though so i can choose which frequency to use.


Too many ‘legacy’ hardware, and I don’t think I have anything 5 GHz capable currently. The first, and only one, was the previous router that died.


I have been using 5Ghz for 6 or 7 years. We had many more issues when we were in an apartment. So many 2.4Ghz WAPs in the area.
The Iphone 5 supported 5Ghz in 2012. All Ipads support it.
Apple has supported it in many of their networking devices since 2007.
My kids’ kindle fires supported it in the previous model.
Not sure my 4 year old Sony TV supports it. I think my Denon and Roku do.


Talking about a dual band router of course :slight_smile:

Alternatively you can get another wifi router and connect it per ethernet and put it onto another channel to alleviate the load.


I have three dual band routers, and only on one I have left the 2.4GHz turned on - mainly for legacy equipment such Pi3 :smiley:
All of them have the 5GHz on, one class N, two class AC, for may various phones, tablets, laptops, Chromecast Audio, Fire TV 4K, that are all supporting it.


Just some suggestions:

Autochannel is usually the best thing to use as it should pick the channel with the “least” interference. If the accesspoint decides to change channels, the connected equipment needs to find it again, needs time and causes potential hickups. Also check whether channel 13 is available, not all equipment supports that channel out of the box. The accesspoint on channel 13 requires that the raspberry is set to a channel 13 allowed country code.

If you do want to use a fixed channel then do a coverage check (use the analyzer on your phone) at BOTH sides of the connection. Interference and difficulties might vary greatly between sides of a house or yard. Pick a channel (preferably out of the three mentioned) which gives you the best options at both locations.

In the end: Frequencyspectrum is scarse. It needs to be shared with others. There are many more options including higher power, directional antenna’s etc., however consider if they comply with local rules and regulations.

Alternatively, consider an extra (cabled) accesspoint closer to your raspberry. Remember: Repeaters and/or extra accesspoint might might your connection better but will also cause more general interference to all. A regular repeater will duplicate your own traffic, increasing airtime by at least 100%.

Good luck!


In US, ch 13 is not available. Well… not legally that is.

A little bit about overlapping. With normal 20MHz channels (G):

With 40MHz channels (N):