5GHz WiFi channel usage metrics

Wireless lan spectrum is crowded, especially if you live on a city or on a flat block, where every other dozen meters there’s a router with default settings competing for the 5GHz band (We won’t even talk about the 2.4GHz band, it is a lost cause) however, even despite how crowded the space is, some channels are consistently underutilized, and I hazard some reasons why ISPs avoid certain channels.

• They want maximum coverage
• They want maximum speed
• They want maximum compatibility

For the reasons above, I expect some bands to be underutilized for the following reasons:

• Short Range Device (SRD) bands limit coverage due to restricted radio power
• 20MHz/40MHz channels are “slow”
• Not all devices support channels above 144

So the theory goes that any channel that falls under any of these restricted categories will be underutilized and available for your use if you can work with the limitations.

The theory, in more detail

If you drop by the list of WLAN channels page on Wikipedia and go down to the 5GHz band, you get a nice chart with the channel numbers for all the channels and the relevant restrictions for different regions, I will be using the EU restrictions as a reference.

With the EU restrictions in mind, we get that some channels look promising since they fall under one or many of the pitfalls mentioned in the previous section.

• 32, 68 and 96 are “slow” by definition, since they can only be used on 20MHz wide network
• 144 is SRD in the EU, which means that when bundled on 40MHz / 80MHz networks those will be limited to SRD too
• 132, 136, 140 either slow or low power SRD in the EU because of channel 144
• 149 to 173 are low power SRD and many devices won’t work with them

All of the above but put into a table, and also showing the 40MHz and 80MHz channels, which combine the bandwidth of the nearest 20MHz or 40MHz channels.

20 MHz	40 MHz	80 MHz	Slow	SRD	>144
32			X
…	…	…	…	…	…
68			X
…	…	…	…	…	…
96			X
…	…	…	…	…	…
132			X
	134		X
136			X
		138		X
140			X
	142		X
144			X	X
…	…	…	…	…	…
149			X	X	X
	151		X	X	X
153			X	X	X
		155		X	X
157			X	X	X
	159		X	X	X
161			X	X	X
165			X	X	X
	167		X	X	X
169			X	X	X
173			X	X	X

Regarding “slow” channels, just how slow they are when compared to the “standard” 80MHz? Presuming 2 spatial streams, which is pretty much the most common configuration I found in the wild, the top speeds end up being:

WiFi	20MHz	40MHz	80MHz
802.11ac	156Mb/s	324Mb/s	702Mb/s
802.11ax	270Mb/s	542Mb/s	1134Mb/s

Gathering data

I decided that since I was having a taxi ride through part of a city, that would be the perfect time to gather data, and in the end I managed to record 1184 unique networks on the 5GHz band as identified by their BSSID, and after massaging the data such that networks using 40MHz / 80 MHz/ 160MHz would count towards all of the underlying 20MHz channels, I ended up with a count of networks hitting each 20MHz channel on a csv spreadsheet (view) which I then put on a chart.

Charts

On the X axis, each 20MHz channel is labeled, on the Y axis, the number of WiFi networks using that channel is counted. Bars are colored to group channels into their 80MHz group, I would have colored the “slow” channels in white but none were found in the wild.

All the 20MHz wide channels on the 5GHz band; Linear scale.

Same thing but logarithmic.

Findings

As expected, the “slow” channels were underused, so much so that not a single network was found in the wild using them. Also, the short range device channels were underutilized, which is by design, since even if a lot of devices were using them, their reach is not great.

An unexpected range of underutilized channels was found on the 116 to 128 channels which despite being perfectly normal channels under EU regulations they had around a tenth of the active networks using them compared to the over saturated 36 to 64 and 100 to 112 ranges.

In conclusion

If you can live with the SRD limitations, where transmit power will make it so you can comfortably cover a room but not much more, move your network there.

If you can live with the slower 20MHz channel, there is a chance that channels 32, 68, 96 and 144 will be completely empty, top speed won’t be the best but reliability will be great.

And last, if enough people use the default “world” setting on their access points, and you live in a place where channels 116 to 128 are available for WiFi, those might be less saturated than other fast & powerful channels.