802.11ac Speeds

Faster, faster faster!!! That’s what we all want right? Faster cars, faster computers, faster Wireless?

 

Well, let’s put the brakes on that for a minute and talk about this.

Let’s talk about what happens when we go “faster” and how we achieve it. Let’s start with Channel Bonding. Wireless uses a 20MHz wide channel to pass traffic, let’s think of this like a 1″ hose. In 802.11n with 5GHz channel bonding, we can now take that single 1″ hose and join it with a second 1″ hose, and basically have a 2″ hose that can spray more data. Sounds great right?!

The other way we get faster is modulation. Modulation let’s you say more in the same amount of space.. Anyone remember The Micro Machines ManJohn Moschitta could say more in one minute than you could. Or if you prefer this analogy, the smaller you can write on a sheet of paper the more information you can get on it. 802.11ac allows for up to 256-QAM Modulation and we can take that bonding and go 20, 40, 60, even 80MHz wide!! ZOMG the speeds, the speeds!! *STOP*

 

Now we need to think a little bit about how this is going to affect the wireless network. So to start a little refresher. In the U.S. we have 3 non overlapping channels in the 2.4GHz spectrum 1/6/11. Now we all know that the 2.4GHz is “dirty”, lots of things can (and do) interfere with it. We also know that with the density that is needed to support BYOD/BYOT that even when the power is turned to it’s lowest setting there are issues with CCI (co-channel interference) and ACI (adjacent channel interference).

In the 5GHz spectrum, we have more channels (9-12 depending on the installation), and a “cleaner” spectrum. For the purposes of this post, we are going to assume we have 12 channels.

 

40MHz wide, if we go with 12 channels, that means we can have 6 channels to use. In most environments that should be fine, really dense deployments like Stadiums aside.

80MHz wide, again assuming 12 channels, we have only 3 channels that we can use. This puts us right back to one of the issues with 2.4GHz, we don’t have enough channels. So let’s hope you’re not doing this.

 

ac_speeds

In the above infogram, you can see the max connected rate and throughput for a an 802.11ac client with 1/2/3SS. Remember this is “theoretical” and perfect world.

802.11ac wave 2 allows for up to 4 SS, and channel bonding of 80-80 or 160MHz wide. If we have issues going 80MHz wide, why would you want to go even wider and have only 1 usable channel? And “usable” it may not be depending on what your neighbors wireless is doing. Adding another Tx/Rx pair to a device is going to, probably, make it bigger. We all want to carry aroudn 17″ laptops and phablets right? That’s why what I’m really waiting for is MU-MIMO.

 

So for all the spiffy new speeds we can get, to achieve those “theoretical maximums” we have to sacrifice our spectrum, which we shouldn’t do. Channel reuse becomes a pain again, even if you are using some automagic channel/power settings.

 

Granted, this is all IMHO, take it or leave it.

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