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160 MHz Channels in 802.11ac Wave 2 - Aerohive Boundless

By Matthew Gast in · Experts · May 6, 2015
Matthew Gast discusses the ins and outs of 802.11ac wave 2 in this series. Discover what this evolution of 802.11ac means for your network.

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.

~~~

Other posts in this series:

1) What Does 802.11ac “Wave 2” Mean and Do You Need it?

2) 802.11ac Wave 2: What Does Beamforming Do For Me

3) 802.11ac Wave 2: Facts and Fictions

4) 802.11ac Wave 2: A Brief History of Beamforming

5) 160 Mhz Channels in 802.11ac Wave 2

6) 802.11ac Wave 2: Regulations around 160 Mhz Channels

7) What Difference Will Multi-User MIMO Make On Your Network?

Matthew Gast (@MatthewSGast)

Matthew Gast is Director of Advanced Technology at Aerohive Networks. He currently serves as chair of both the Wi-Fi Alliance's security task groups, was the first chair of the Wireless Network Management Marketing task group, and is the past chair of the IEEE 802.11 revision task group. Matthew is also the author of 802.11 Wireless Networks: The Definitive Guide (O'Reilly), which is now in its second edition and has been translated into six languages. His companion book, 802.11n book, 802.11n: A Survival Guide (O’Reilly), was recently published and provides information on how 802.11n works and what it means for the WLAN planning process. Most recently, Matthew completed 802.11ac: A Survival Guide (O'Reilly).