November 07, 2013

Migrating to 802.11ac – 3 Key Considerations

802.11ac has evolved Wi-Fi technology providing greater speed and throughput compared to previous generations. Yes, I’m excited about the evolution, as everyone in our industry is as well. It fascinates me to consider revolutionary steps in Wi-Fi, such as MU-MIMO (Wave2), which will change the game in terms of capacity, density and design in the future.

Trust me, we will need all the help we can get.

Mobile devices, and the explosive use of applications, will continue pushing the 802.11 medium to its limit. The unwritten rule of network administration is that bandwidth will be consumed at the same rate it becomes available. Adding bandwidth doesn’t solve all problems, but it certainly is an appealing measure to employ when available.

As marketed, 11ac Wave1 technology is targeting Gig rates over the air.  Compared to previous generation Wi-Fi protocols the performance gain is a factor roughly 2.5x.

So where does the performance boost in Wave1 come from? It’s a combination of two enhancements: Wider Channels and Denser Modulation. That’s it. We’ve expanded the two-lane Wi-Fi road to a four-lane highway and we’re filling it with more cars.

There’s no turbo charger or nitrous in the AP making it faster. The four-lane highway in my analogy is new 80Mhz wide channel, and the increased cars from doubling the amount of bits per wavelength sent with 256 QAM modulation.

Don’t get me wrong – this is really cool evolution and I’m not underselling it – but there are elements of Wave1 11ac that aren’t widely discussed. It is, without question, worth understanding these 3 aspects if your expectation is set to achieve very high data (VHT) rates in your deployment.

1. Client Capability: Probably the most overlooked aspect of Wireless networking: the clients. It’s a two-way street in Wi-Fi; faster APs don’t mean much if the clients aren’t capable. This isn’t a knock against client vendors, but reality is that all clients are not created equally. My beloved iPad mini simply can’t keep up with my new MacAir in a Wi-Fi race. Consider the clients that will be deployed in your environment to ensure expectation is aligned and resulting speeds are achieved.

A simple 5Ghz. comparison chart to aid (check your preferred client vendor’s datasheet for their specifics):

2. Implication of Wider Channels: The availability of 80Mhz channel width doesn’t answer an important question – Can it be used in an enterprise deployment? The immediate concern of 80Mhz channel is implication of co-channel interference when backing down to narrow channels (20Mhz/40Mhz) to support legacy clients. This interference is a likely occurrence in a densely populated AP deployment where legacy clients remain active and it will negatively impact overall network throughput. Consider the implication and potentially design for 40Mhz/non-overlap today leaving best effort availability of 80Mhz. where feasible. The result of this decision will affect the outcome and resulting data rates you are hoping to achieve in your network. Said another way: 11ac requires channel planning. This is not a simple plug and play exercise as some suggest.

3. Implication of 256 QAM Modulation: The new modulation technique has requirements that are relatively easy to understand – line of sight and proximity to the AP – in order to work. Failure to meet these requirements will downgrade to previous generation 64 QAM modulation and essentially cut throughput in half (less cars on the road). In addition, it is worth noting that 256 QAM modulation requires a relatively clean RF environment and greater signal-to-noise ratio (SNR) to operate.  This will have direct implication on how you design for 11ac signaling with likelihood to target -55dBm and placement of APs close together. When compared to a typical -65dBm utilized in many 11n designs you should realize that more APs are in fact required. This again is a direct implication, as clients will need to be closer to the AP to acquire strong/clean signal and achieve VHT rates.

Real world vs. theoretical is always a hot button topic in the technology industry. This couldn’t be closer to the truth with Wave1 11ac technologies. Planning, and more importantly, achieving the desired outcome with your 11ac project will take consideration and understanding of the elements discussed here.

Successful wireless deployments happen in the planning phase; there’s no luck involved. Keep these three aspects top of mind as you plan for 11ac: The Client capabilities, ability to deploy Wider Channels, and the requirements to achieve Dense Modulation.

Harmonizing these 3 key factors will lead you on a path to success.

I’m interested in your feedback. Please leave a comment, or engage with me via twitter (@mikeleibovitz).

About The Contributor:
Mike LeibovitzDirector of Mobility Solutions

Mike Leibovitz has over 15 years of Sales Engineering, Product Management and Marketing expertise in the Communications Industry. Since 2008 Mike has been instrumental in bringing high density Wi-Fi solutions to stadiums, healthcare, education and commercial markets for Extreme Networks. Mike’s current role, Director of Mobility and Applications at Extreme is focused on evangelizing mobile and software solutions that drive positive and consistent user experiences. If you would like to read more about his views on mobility, visit his blog Follow me on twitter @MikeLeibovitz.

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