Skip Links

802.11ac boosts buzz more than bandwidth

A great innovation, 802.11ac does more for 802.11n than it does to change the face of wireless networking

By G.T. Hill, director of technical marketing, Ruckus Wireless, special to Network World
January 27, 2012 12:15 PM ET

Network World - Although vendor-written, this contributed piece does not advocate a position that is particular to the author's employer and has been edited and approved by Network World editors.

The buzz about 802.11ac is in full swing, but don't believe everything you read.

The newest of Wi-Fi innovations, 802.11ac (still in draft form) looks like it will start making it into enterprise Wi-Fi products as early as 2013 and home products even earlier. It's already being flaunted as Gigabit Wi-Fi. And for the largest Wi-Fi market, the home, it will be. But will it deliver gigabit speeds for the enterprise? Not a chance.

CES: Gigabit Wi-Fi takes center stage

REPORT: Full steam ahead for Gigabit wireless

Defined for the capacity-rich 5GHz spectrum (495MHz) only, 802.11ac introduces a number of new techniques like advanced modulation and encoding, multi-user MIMO and channel bonding, that theoretically, if you're talking to a vendor anyway, has the potential to dramatically increase Wi-Fi capacity. The question is, REALLY?

Make no mistake, 802.11ac is a great innovation. But like any great innovation, the devil is often in the details. So here are some details that should help demystify 802.11ac. Here are the key differences to understand:

* Eight spatial streams. One of the biggest Wi-Fi innovations came with 802.11n in the form of spatial multiplexing using a technique called MIMO (multiple input, multiple output). MIMO is the use of multiple antennas at both the transmitter and receiver to increase data throughput without additional bandwidth or increased transmit power. Basically it spreads the same total transmit power over multiple antennas to achieve more bits per second per hertz of bandwidth with the added benefit of greater reliability due to more antenna diversity.

In essence, MIMO lets an access point send multiple spatial streams to one client at a time to increase capacity. 802.11n specified up to four spatial streams.

Now in glorious one-upmanship, 802.11ac will support up to eight spatial streams. Historically it has taken chip manufacturers about two years to add an additional spatial stream (802.11n is only at three right now). While that will surely improve with 802.11ac, don't look for it to ever get to eight. However it would be a funny sight to see. Just picture an AP with 12 omni-directional antennas (eight for 11ac in 5GHz and four for 11n in 2.4GHz) sticking out of it. Not a pretty picture.

* Multi-user MIMO. Another difference with 11ac is support for "multi-user MIMO" (MU-MIMO). With 802.11n, MIMO could only be used for a single client at any given time, while 802.11ac tries to improve on this by supporting multiple clients.

This allows an 802.11ac AP to transmit two (or more, depending on the number of radio chains) spatial streams to two or more client devices. This has the potential to be a good improvement but is optional. And it's expected that the first 802.11ac chips out the door won't support this. What's more, there's is a good chance that MU-MIMO won't ever be supported due to the radio and MAC complexity required.

Our Commenting Policies
Latest News
rssRss Feed
View more Latest News