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802.11ac Deeper Dive Webinar Recap

by Matt on Jun 30, 2014

Last week, AirTight's Senior Technical Marketing Engineer, Robert Ferruolo (@RAFerruolo), added another chapter to the AirTight 802.11ac webinar series. Robert presented on "802.11ac Deeper Dive" focusing on features that come along with the 802.11ac wireless platform.

Webinar recording image

During the presentation, Robert broke down channel availability, QAM, beamforming, MIMO, MU-MIMO, frame aggregation, and error correction. To view the recording, click here.

Throughout this 6-part series, we'll continue to break down why 802.11ac should be a serious consideration for your wireless network. The series will address the inevitable migration from 802.11n to 802.11ac.

We'll be continuing to post our Q&A sessions for all of our webinar series. Stay tuned for more updates on upcoming webinars and their corresponding Q&A sessions.

Upcoming Webinars: "Is 802.11ac Right for Your Network?" & Beyond

Our third installment in the series takes place on July 23rd with “Is 802.11ac Right for Your Network.” Future presentation in our 802.11ac series include:

  • Is 802.11ac Right for Your Network” - registration now open for the webinar on July 23
  • "802.11ac Deployment Best Practices"
  • "802.11ac Channel Capacity Planning"
  • "802.11ac Network Optimization"

Our speaker, Robert Ferruolo, has over 20 years of experience in networking and over 10 years in the wireless industry. What makes Robert qualified to speak on 802.11ac? Beyond his extensive tenure in the wireless industry, Robert is an 802.11ac enthusiast, has been conducting competitive performance testing for over 8 years, and has authored numerous 802.11n and 802.11ac best practice guides.

If you’d like to receive more info on any of these future discussions, please send your questions to

Recent Webinar: 802.11ac Deeper Dive

Below, you’ll find the link to the recorded presentation, a copy of the slide deck, and questions from the event, along with our answers.

Recording: 802.11ac Deeper Dive (Free registration)

Slides on Slideshare:

Q&A session from 802.11ac Deep Dive Webinar

Q: Any numbers on how much better SNR 256-QAM needs to be compared to 64-QAM?

A: An SNR of 25 is typical recommended for 11n/64-QAM. For 11ac/256-QAM rates (MCS-8 and MCS-9) the recommendation is to design for an SNR of 32 – 36.

Q: Just how far apart does the 1ss clients need to be in order that MU-MIMO to work? (...and if they move?)

A: We do not actually know as we have not tested yet. In theory it is more a matter of client-to-client spatial diversity (i.e. per client channel state differentiation) than physical distance, of course the two are related to some degree. In a mobile environment it is all the more important to regularly sound the channel (somewhere around the order of every 10 ms) so changes in clients’ channel state are factored into the AP’s steering matrix.

Q: Do you have any information on 802.3ad?

A: The C-75 does not currently support 802.3ad. We will likely implement link aggregation on future 802.11ac APs, particularly on Wave 2 APs where the throughput capabilities will easily oversubscribe a single GigE uplink.

Q: Do you recommend deploying 802.11ac using 80MHz channels?

A: Some deployments can definitely use 80 MHz channels as this will allow the network to be able to meet the demands of higher throughput applications like video. However, the minimum number of non-overlapping channels recommended for an 80 MHz deployment is 4. Using 4 or more unique channels will help minimize CCI and ACI (Co-Channel Interference and Adjacent Channel Interference). For some regulatory regions this may require use of DFS channels. There are some environments where using 40, or even 20 MHz channels might be preferable, such as with stadiums, where the combination of very high client density and openness of the environment can benefit from many different 20 MHz cells rather than fewer 80 MHz cells, where channels need to be reused more frequently.

Q: Can video streaming benefit from frame aggregation?

A: Video streaming services like Netflix and Hulu can benefit from frame aggregation as both are transported using HTTP/TCP. With real-time video streaming (unicast or multicast) over RTP (Real-Time Protocol) large frame aggregates are less helpful so they are not as likely to be used. Of course with 11ac all transmissions are sent using A-MPDU frame aggregation but with RTP applications the aggregations are typically smaller. One interesting note is that video streaming over RTP scalability is impacted by this lack of large frame aggregates.

Q: Can Airtight suggest any good performing 802.11ac clients?

A: During our 1st session in this 802.11ac webinar series we included a slide that lists a number of 11ac clients that are currently available. Two client that performed particularly well in our test labs are the MacBook Air, which is a 2 spatial stream 11ac client and the MacBook Pro, which is a 3 spatial stream 11ac client. The presentation for the 1st session, “Introduction to 802.11ac”, is available in our blog post with the recap of 802.11ac Essentials webinar.

Q: When designing a network for 802.11ac and deploying dual band access points, shouldn't you be concerned about high CCI in the 2.4 GHz band?

A: Considering that there are typically going to be more 5 GHz channels available than non-overlapping channels in the 2.4 GHz band (e.g. 1, 6 and 11) and that 2.4 GHz propagates farther than 5 GHz, it is very likely that networks designed for 5 GHz coverage will result in high levels of CCI and ACI (Co-Channel Interference and Adjacent Channel Interference) in the 2.4 GHz band.

However, there are a number of techniques that can be used to help mitigate this issue. One of the first configuration changes to make is to reduce AP transmit power for the 2.4 GHz radios. Another recommendation is to turn ¼ or so of the 2.4 GHz radios into full time WIPS sensors. These techniques should help but it often not enough for very high AP density designs, like what you would expect if the network were designed for pervasive support of 256-QAM enabled rates (i.e. MCS-8 and MCS-9). For these types of deployments it may be necessary to power off a percentage of 2.4 GHz radios. Please note that we will be covering these types of deployment best practices in an upcoming session, “802.11ac Deployment Best Practices”.

Q: We’re considering deploying 802.11ac access points in our high school gymnasium, but we’re not sure how many APs will be required. Can you offer some guidance?

A: In order to determine how many APs are required we would first need to know the following:

  • Square footage/meters of the gymnasium
  • Types of clients that will be in use
  • Peak number of clients that will be active simultaneously
  • Per client throughput SLA or the types of applications that will be used

Once you have this information you can perform channel capacity planning. The process uses simple math to determine how many APs would be needed for a given set of requirements. We will be discussing channel capacity planning in a future session of this webinar series .

Q: What are the maximum distances that MCS-8 and MCS-9 (256 QAM) rates can be supported?

A: Data rates that require 256-QAM are typically going to be possible when the distance between the transmitter and receiver is 25 feet (7.62 meters) or less. One thing to keep in mind is that the signal strength requirement to support 256-QAM increases as channels get wider. The table below lists that approximate signal strength requirements to support MCS-9 (the highest rate in 802.11ac) for various channel widths.

Modulation Code Scheme

20 MHz

40 MHz

80 MHz

80+80 MHz

160 MHz

MCS-9 (256-QAM) -57 dBm -54 dBm

-52 dBm

-49 dBm

-49 dBm

Join Us for the Next Event!

Please join us for our upcoming webinar on July 23rd at 11am EST and 9pm EST on “Is 802.11ac Right for Your Network?.” In this 30 minute webinar, you will learn about:

  • Determining if 802.11ac is the Right Choice
  • 802.11ac Use Cases
    • Hospitality
    • Education
    • Law enforcement

See you on the webinar!

Topics: WiFi, WLAN planning, 802.11ac, WiFi Access