All Things 802.11ac - Question 1: What is 802.11ac?

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  • Updated 5 years ago
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Good morning/afternoon/evening to everyone! I'm very pleased to have the opportunity to spend the day with all of you, and especially Matthew Gast, on All Things 802.11ac. No one knows more about this topic than Matthew - he did, after all, quite literally write the book on this subject. I'll be posting a new question every hour, with the last one at 4:00 PM (pacific time) this afternoon. Matthew will be here all day, as will I, and I hope you can hang around as much as possible as well. Please feel free to join in the conversation - post your own questions, comments, and dig as deep as you'd like. Everything .11ac is fair game today, and it's our objective to explore this exciting topic to the breadth and depth you'd like. Thanks again for being here!

OK, Matthew, good morning to you! The sun's up here on the east coast, anyway. Let's get rolling with the Big Question: What is 802.11ac? What are its general parameters and features, and how does it differ from 802.11n?
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Craig Mathias

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Posted 5 years ago

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Matthew Gast

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The sun is not up on the west coast yet, so I'm a bit jealous of you. I think I've got a bit under two hours until sunrise out here...

802.11ac is the fifth generation of 802.11, building on a more decade of increasing speeds:

First generation = 802.11 frequency hopping or direct sequence, 1 or 2 Mbps
Second generation = 802.11b, 5.5 or 11 Mbps
Third generation = 802.11a and 802.11g, 54 Mbps
Fourth generation = 802.11n, up to 600 Mbps (in the standard) and 450 Mbps (in real products)

In the fifth generation, we get much higher potential speeds. The 802.11ac standard goes up to 7 Gbps, though the first products to come out will "only" be capable of 1.3 Gbps.
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Tony Boudro

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How long until products will be "more capable" of the anticipated 7 Gbps that the 802.11ac standard allows?
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Matthew Gast

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802.11ac, like 802.11n before it, will be following the curve set by the chipset vendors. The first wave of chips is out and is being built into final products (APs and clients) now. The second wave of chips is out soon, with shipping products to follow next year.
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Matthew Gast

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802.11ac has four major features that distinguish it from 802.11n:

1. Wider channels - 802.11n supported 20 MHz and 40 MHz channels. 802.11ac adds 80 & 160 MHz channels.
2. 256-QAM. This is an improved modulation that packs more data bits into the same period of time, increasing efficiency of the radio link.
3. More spatial streams. 802.11ac supports up to eight spatial streams compared to 802.11n's four.
4. Standardized beamforming. Instead of many options for beamforming, 802.11ac chose one method of beamforming, which should improve the number of implementations. Beamforming is used to create multi-user MIMO, which has the potential for greatly increased effective speeds.

In the initial wave of products, we'll be taking advantage of the first two big features.
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Craig Mathias

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We'll spend more time on wider channels and beamforming in upcoming hours, and MIMO, streams, and MU-MIMO this afternoon (eastern time).
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Nick Lowe, Official Rep

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Should 256-QAM change our deployment strategies? Should we now deploy more APs with smaller cell sizes closer to the clients?
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EvaldasOu

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Hi WiFi Experts!

That's a big question and of course you know more than me...

802.11ac is about speed, modulation and MU-MIMO!

As Matthew mentioned above, 802.11ac speeds are tremendous!

We get this because :
1) Increased channel width : beyond 40MHz, up to 160MHz.
2) Increased number of spatial streams: more than 4, up to 8.
3) Improved modulation technique :256-QAM, 802.11n can use 64-QAM.It is 8 bits per symbol versus 6 bits per symbol.
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Brent Bischoff

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Does 802.11ac impact the site survey & AP design methods and planning for LBS?
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EvaldasOu

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Of course it will! The main reason for this is wider channels, and higher throughput! Adjacent and co-channel interference may become a real challenge!

Just imagine, 160MHz wide channels on 5 GHz band. What will happen when all the companies will start to deploy 802.11ac?
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Craig Mathias

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We'll return to the 160-MHz. channel issue later - that's a very interesting question.
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Matthew Gast

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Planning for location services requires lots of APs, whether you run the network using 802.11n or 802.11ac. There will be a few changes, but you'll need a lot of APs either way!
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Craig Mathias

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Absolutely true. I've been working over the summer on a number of Wi-Fi location and tracking projects for very large venues, and the coverage-based deployments, a byproduct of the traditional site surveys they usually do, really don't cut it for LBS. As before, think capacity, and the LBS issue is on its way to being solved.
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Matthew Gast

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Nick asks: "Should 256-QAM change our deployment strategies? Should we now deploy more APs with smaller cell sizes closer to the clients?"

256-QAM requires something like 5-7 dB over 64-QAM. In practice, that is worth a wall or two. I expect 256-QAM to be effectively a line-of-sight feature because there just isn't that much signal to spare in most links.