Quick Take: Wider Channel Widths Are Flashy but Not Efficient

I've been thinking of writing a well-articulated blog post on why the preference for high-density Wi-Fi networks is smaller channel width over larger channel width. This post is NOT that.

Instead, I was on Twitter articulating some of the logical points why smaller channel widths provide better aggregate capacity than larger channel widths (assuming you deploy enough radios and take advantage of all the spectrum at your disposal). Here is a quick recap of those points.

You might want to reference my SNR to MCS Index Mapping Table, which shows why larger channels result in a reduction in modulation rate that can often offset the gain from using the wider bandwidth in the first place. And my 802.11ac Receiver Sensitivity charts show that you have to have a really great signal strength for wider channels to even be considered, but watch out in your design because overcompensating to achieve higher signal strength will increase co-channel interference (CCI) which travels a LONG ways! Finally, my post on 802.11ac Adjacent Channel Interference (ACI) shows that wider channels create more ACI than smaller channels, and ACI is even more detrimental and unfriendly than CCI. Therefore, radio receivers require greater adjacent channel rejection (up to 8dB more), and with fewer channels for frequency re-use ACI is more likely.

802.11ac data rates clients can expect at -67dBm: 20 MHz 72 Mbps 40 MHz 135 Mbps 80 MHz 260-292 Mbps 160 MHz 390 Mbps pic.twitter.com/bCK1rcPQn9
— Andrew von Nagy (@revolutionwifi) August 21, 2014

Wider channels result in reduction of effective modulation rate, seriously reducing their benefit unless clients have a GREAT signal. #WiFi
— Andrew von Nagy (@revolutionwifi) August 21, 2014

Wider channels also result in more clients sharing fewer channels and higher medium contention, degrading network performance. #WiFi
— Andrew von Nagy (@revolutionwifi) August 21, 2014

In high-density networks, better off using a greater qty of smaller channels. Better modulation rates, less contention, higher agg capacity!
— Andrew von Nagy (@revolutionwifi) August 21, 2014

Wider #WiFi channels add little addtl efficiency for networks; just a few net greater subcarriers and Mbps over multiple smaller channels.
— Andrew von Nagy (@revolutionwifi) August 21, 2014

Wider #WiFi channels just provide the pop & flash of higher single-client speed, but do little to increase effective network capacity.
— Andrew von Nagy (@revolutionwifi) August 21, 2014

It really comes down to how many channels do you have for re-use, how much clients contention, and how many radios can you afford to deploy?
— Andrew von Nagy (@revolutionwifi) August 21, 2014

The preference for aggregate #WiFi network capacity is smaller channels, more radios, more channels to re-use, less contention...
— Andrew von Nagy (@revolutionwifi) August 21, 2014

You have to be willing & able ($) to deploy more radios on smaller channel widths. #WiFi
— Andrew von Nagy (@revolutionwifi) August 21, 2014

If you can't deploy enough #WiFi radios on smaller channels to use all spectrum available to you, that's when you consider larger channels.
— Andrew von Nagy (@revolutionwifi) August 21, 2014

Cheers,
Andrew