This post continues the 802.11ac wave 2 series, dissecting each feature in the “wave 2” grab-bag of technologies. First up, I’ll be 
looking at 160 MHz channels.
Conceptually, 160 MHz channels are neat because when you increase the channel width, you increase capacity. One common way of referring to “wave 2” speeds is to say that such devices may go up to 3.5 Gbps, a speed that is only achievable when using 160 MHz channels.
How realistic is it to talk about using such wide channels? Let’s start off by looking at the available spectrum, using the following excerpt from 802.11ac: A Survival Guide.
This excerpt shows only the channel map in the USA, but channel numbers are the same throughout the world. Each row in the figure shows how the available spectrum is channelized. (For now, ignore the differences in shading, which illustrate differences in regulatory treatment at the time the book was published.)
802.11ac offers two options for creating such wide channels, referred to as 160 MHz channels or 80+80 MHz operation. Both have the same data rates and transmission capacity, but they use the radio spectrum slightly differently.
- In 160 MHz operation, the radio channel consists of a single 160 MHz channel, and is conceptually identical to any other Wi-Fi channel, just wider. A 160 MHz channel is shown in blue in the following figure.
- In 80+80 MHz operation, the 160 MHz channel is created by bonding transmissions on two different 80 MHz channels. Both channels must be used simultaneously, and for the same purpose. A device may transmit on both, or receive on both, but the 80+80 mode does not allow you to use one channel for receive and one for transmit. The two channels in 80+80 mode are not contiguous, and can be located clear across the band.
While the two options are similar on the surface, there are important implications for the way that hardware is built. In the 160 MHz operational mode, the hardware looks like most Wi-Fi hardware to date.
At a high level, you have “one” of everything, just like you did on narrower channels. Because the 80+80 mode transmits on two channels at the same time, additional hardware is required. Not surprisingly, you have “two” of many of the radio front-end components.
Although the 80+80 MHz mode requires additional hardware complexity, it is not hard to see why it is attractive. Under the current regulations, there is one 160 MHz channel, and five 80 MHz channels. By using 80+80, it is possible to take advantage of higher-speed operations much more often.
Though, as we’ll see in the blog series, it may not always be possible to use the fullest capacity.
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Other posts in this series on 802.11ac wave 2:
What does 802.11ac "wave 2" mean and do you need it? (By Matthew Gast)
Wait on 802.11ac Wave 2 until mobile devices catch up (by Metka Dragos)
Deploying 802.11ac won't force a wired network upgrade (by Metka Dragos)