CWNP CWNA – Very High Throughput (VHT)

1. Very High Throughput (VHT)

Now in this module, we’re going to talk about what is now called very high throughput, which won’t be that in ten years from now, but anyway, it’s going to be the eight to eleven AC 2013 amendment. Now, this is a wifi that operates only at 5 ghz, but they can combine channels. Instead of having just 20 mhz, they can go 2040 8160. They change the way in which they do of the modulation to be able to send eight bits of data instead of six.

So now when you think you can have four times as wide a channel and in each one of those channels have more data sent, then you can’t understand why they’re calling it the first gigabit per second WiFi. So we’ll talk a little bit about the modulation, the coding schemes. We’ll look at the single user or mimo. We’ll also look at the multi user, the mu, I guess what I’m going to call it Moomimu, the multi user mimo and see how that affects data rates. And by the way, things that I’m going to talk about have been an amendment, but they are not ready in hardware yet.

2. 802.11ac Part1

So let’s compare the high throughput through the very high throughput. And you have to remember that the high throughput came out in 2013. And while I’m talking to you about this video, it’s not very far away from that, but we’re already at the 800 and 211 AC because of the needs for multiple channels, AC only operates at the 5 ghz band. Now, the big thing here is in the way in which they do the modulation. So they’re still using ofdm, but how they encode information into that is going to continue to increase and increase and increase. So the 16 qam and the 64 qam, those are pretty good and we still have those.

But look at what they did. They upped it by another factor of two with the 256 qam, which really just means, again, we’re going to send four times as much data in each one of these channels. The channel bonding you’re going to see goes from the 20 and 40 to the 80 and 160. And by the way, remember this bonding was kind of a problem that we had with the 2. 4. We could have done more if we weren’t trying to work on both of the frequencies up to eight spatial streams. Remember, each one of those is a separate set of communications instead of four. I’m looking just for other things that have changed, explicit beam forming.

And we’ll talk about that as we get in there to see what that beam forming does for us. But there’s a great way for AC to be able to either talk to just one host or up to four hosts by focusing the antenna strength and getting even further distance. What else do I think is all the frames are? Again, remember, Mbdu is how I talk to the layer above and the layer below. They do support single user like and did, but multi user up to four users at one time to get better distance. So that means we can have then up to four simultaneous user transmissions and potentially, I called it gigabit service, but potentially we can get almost seven gigs of throughput on the AC. The reason I’m calling it one gig now is that’s where we are with technology. But as the chipsets begin to improve and to catch up and how rare is that, that we actually have to get the hardware to match the actual protocol? We have some great room for growth.

3. 802.11ac Part2

Now, when we first introduced channel bonding and getting from a 20 to 40 mhz channel on 800 and 211 N, and at 5. 0 least, we had many other non overlapping overlapping channels, but we had potentially just the three overlapping, which really made it hard for a very big deployment of eight to eleven N, because we only have the three channels. So the existing enterprises really can’t work with the 40 mhz channels very well because of what I just said. If you have a cell that’s using two of three channels, then what do you put next to it without having interference and having the overlap? And so that’s why 5 ghz really makes sense. And that’s what they did with AC. They said, you know what, there’s no more 2. 4, we’re going to go to the 5 ghz radios.

4. 802.11ac Part3

So Eight or 211 AC is just a better evolution of the enhancements that we had with the Eight or 211 Amendment. I mean, we were apparently going forward with some really good ideas with eight or 211 N, so they just took it a step further. But at the same time they said, hey, we’re using ofdm. Which is a great way of modulating the information to be able to send it over that 5 ghz channel even if it was only 20 wide. So now that we can get even more information on a single 20 mhz wide channel, what’s going to happen when we have two or we have four channels put together?

We’re going to get a big increase in speed because we’re sending more per channel and then we can have wider channels. So if you have even just two of those 20 mhz channels bonded together and again, remember we had a little bit more of the subcarriers for us to be able to use. And as we keep increasing that, we have even more subcarriers, then we’re going to be able to send a lot of data. And that’s great at the top end, but you have to remember that it’s again, the reason why we’re not on two 4 ghz with this particular type of transmission.

5. 802.11ac Part4

So originally we would take these 20 mhz channels and we are talking about 5. 0 ghz here and, and we could pretty much just say, hey, let’s take channel 36, add another channel and so what do you call it? You don’t call it 76 because that’s the channel way over there. They just called it channel 36 plus one. Or it could have been channel 36 plus three. But either way, we’re now identifying that we have a 40 mhz channel. And when we talked about high throughput, we talked about one of them considered as the primary, where we’re going to do a lot of the signaling and then one to help carry the data, which they’re going to call channel 40, which is what it is, even though they might have called it 36 plus one. And this isn’t the only example, there’s many others. But I mean, look at what we’re getting. 256 subcarriers when we go even bigger, instead of just going 40 mhz wide and we go to an 80 each one of those sub carriers can carry a lot of data for us, which is what’s going to help improve especially, like I said, with the way in which we’re doing the modulation. So 234 data sub carriers, only eight pilots, that’s four on each side and then a few of them are let’s alone again to give you that little bit of buffer space between the channels.

6. 802.11ac Part5

So after the 20 and the 40 and the 80, the next one was a 160 mhz channel. And you probably guessed that that means that we have 280 megahertz channels that were bonded together. But what’s really nice about this is they do not have to be adjacent like they were in the 2. 4. So I could have an 80 mhz channel on one part of the band, another 80 mhz channel on the other part of the band.

They can still work together. Now, if the channels are adjacent, then we would call it 160 mhz channel. But if they are separated, then we would call them the 80 plus 80 mhz channel. And I really guess the plus sign just simply means the channels are not adjacent. But it doesn’t mean we’re not using them for our transmissions.

7. 802.11ac Part6

Now in the 5 ghz range. You might think finding four channel groupings isn’t going to be that difficult. But it does. If you consider what we’ve talked about with things like site surveys and everything else. If I put an access point here and I’ve got this cell coverage, but I’m using four channels and I only have twelve channels to use, then okay, I can put another one here that’s non overlapping and now I’m up to eight channels. But then when I start putting the other one and remember again, we only get to use eleven in the Us. Somewhere in this grouping I’m going to have some overlap.

So it can be a little bit more difficult in choosing the way in which you do the channel bonding because of the fact that somewhere you might have some overlap. So I mean, here you see some examples, right? I can use 36 and 40 to make this 40. Or I could use these for here for the primary channel for an 80. And if I wanted to do an 80 plus 80, then I’m pretty much using all of them, aren’t I? And so if each of these cells was using the 80 plus 80, or in this case it would have been 160, don’t have room for overlap without causing some interference.

And so that does make it a little bit more difficult. But in those situations in which you have just one access point to cover your house or something else excuse me, a little bit bigger circle there, then it’s not a problem. So it’s just a matter of the design and what you’re trying to accomplish.