CWNP CWNA – High Throughput (HT)

1. High Throughput (HT)

We’re going to talk about what’s called high throughput, which, in other words, is what they described the standard or the amendment for 800 and 211 n. So we’ll look at that amendment, we’ll talk about the wifi Alliance, get some idea about the multiple input, multiple output, and what channels are used for high throughput and what’s different at the Mac layer.

2. 802.11n -2009 Amendment

So the amendment eight to eleven N 2009 defined high throughput as or the cause anyway, as radios that use multiple input, multiple output or mimo technology in unison with the ofdm type of multiplexing or I should say modulation technology. The benefits then is that mimo having more than one channel gave you an increased throughput, and of course, ofdm was able to encode more characters into its actual transmission of the data. So we’re hoping, anyway, that we’re doubling almost everything when it comes to the throughput.

3. Wi -Fi Alliance Certification Part1

So part of this wifi Alliance certification is that they look for the features that were a part of this standard of this amendment. And that is you had to have a support for two spatial streams, which at minimum would make it mimo, because that’s what it was about. Multiple input, multiple output. That means that you had to have an access point that can transmit and receive on at least two spatial streams.

And client stations are required to transmit and receive on at least one special or spatial stream. And that was all mandatory for the bare minimum of what we needed. For 811 N, we could go up to three spatial streams, which, by the way, would mean three separate radios. That’s why often when I’m making fun of my access point that I draw with these little external antennas, I tell people, look, let’s make it 811 3rd antenna on there. And so that means the access points and the client stations have to be able to transmit and receive these streams. And it is something that is optional, but it does create higher throughput.

4. Wi -Fi Alliance Certification Part2

Now as we continue to look at some of the other requirements for features, not all of them I’m going to hit you up with here, except for the ones that sound more exciting, but we should at least look at what’s mandatory. And we’re going to get a chance to talk a little bit more about these Mac pdus that we have. But they had to support the Mpdu and the msdu in the receive mode and the ampdu for the transmit mode and was a requirement for all of them. And remember, what these pdus were, were methods of being able to communicate up and down the osi stack.

They had to support block acknowledgments because again, not acknowledging each and every packet or frame, each and every time gave us better bandwidth as well. So this is requirements, as it says here, for all of the operations. Now, it was best working for you on the 5 operation.

The reason I say that there’s more channels in that 5 ghz frequency, which meant that we had the ability to eventually move up to using even more and more channels for one transmission, getting to double or even triple the speed. It was supported to some extent in 2. 4 where we could at least use two out of the three channels. But you didn’t have quite the throughput you did at the 5 ghz range, but both of those were optional, unlike what you’re going to see with 811 AC where it’s mandatory that it can only operate at the 5 ghz operation. Now the other nice thing is that because it could work in 2. 4, it was easier for us to migrate older machines into 800 and 211 N, because we did say, hey, in N you have to have backward compatibility for the bng that are operated at 2. 4. Again, not mandatory, but an option and something that the wifi Alliance would test.

All right, 40 mhz channels in the 5 ghz band. You see this is good because remember, all of the channels are just 20 mhz as we were looking at these non overlapping channels. And if I’m going to pull the channel adjacent to me and add that together for a 40 mhz channel, I’m basically doubling the bandwidth. The problem is if that’s channel one and that’s channel six at 2. 4 ghz, then the only channel left for me is channel eleven.

And that can be disastrous when you’re trying to plan for the coverage anyway, which was actually down here, I’m sorry, the coexistence mechanism for the 2. 4 in the five gig band where we have twelve channels, this becomes very easy to be able to bond the two adjacent 20 mhz. In fact, you’re going to find out that you can make that channel even wider with AC.

So again, optional stuff here all the way through and then the rest of it just gets us into some of the other types of AC protection mechanisms. Like still, because the two channels are together. Do we really need to have that little space in between for the guard mode and things like that? All of those become optional. But I gave you the ones that I think are the most important ones for you to know.

5. MIMO Part1

Now, the heart and soul of eight or 211 N exists at the physical layer with the use of a technology that we again keep calling mimo, the multiple input, multiple output. In other words, where multipath used to be bad for us, now it’s severely good for us. So mimo requires multiple radios and antennas, and they call them radio chains. Now, to tell you the truth, when I say that you might think I have to have, what, three separate access points? And the answer is no. It’s just that that access point would have three, or usually would have three antennas.

Each antenna would have its own source of AC power for the transmitter, its own cable from the transmitter to the antenna. And it would just occur that you would have three of them in one box. So you still see one box, but each one of those setups they call a radio chain. Now, the transmitting of multiple streams of data is

done with a method they call spatial multiplexing, which is giving you better throughput and is trying to take advantage of multipath, by the way, in which it spaces apart each of the signals. They can also, again, use multiple antennas to provide for better transmit and receive, as we said before. And because of that, it can also increase the range and the reliability. In fact, we can overcome a lot more of the noise floor with the signals that we’re sending.

Now, there are different types of transmit and receive diversities. You’re going to see a couple of them as we go through and talk about 800 and 211 N, like things like the space time block coding. And I like that name because I’m somewhat of a science fiction buff. So that term space time just sounds cool. The cyclic shift diversity and other types of transmit diversity techniques where what we’re trying to do is take advantage of the multiple antennas in the multiple channels.

6. MIMO Part2

So here’s an example of mimo. And what’s really important to remember is that this is one access point. It’s just got three antennas. And what do we say with the receiving device that you had to have at least two antennas, if not three, depending on what you need to do. And so you can see that as we’re sending the data, we’re just taking taking advantage of each of these having their own independent streams. So stream one, stream two, stream three.

So we can basically send all of this data to the devices that are receiving. And I don’t know why they wanted to show you a full mesh, but that’s all we’re attempting to do now. What is really kind of cool about this is when you think about what happened in the days where multipath was bad for us, multi path was bad for us because we had one antenna sending a signal to somebody who wants to receive, but it was also bouncing off of walls and chairs.

And so you might have been receiving these three signals but they were the same signal, they were just not coming to you at the same time point in time. And so that caused sometimes problems where I am now sending three unique signals kind of like you got in the picture at the bottom, but each one with a different set of data.

7. MIMO Part3

So your conventional 800 and 211 radios would transmit and receive by using what they call the single input single output, or the siso. And so that would just be a time when I had just one antenna, one radio chain. Now, I think I told you this already, but the radio chain, the definition is a single radio and all of the supporting architecture, that would be mixers, amplifiers, your analog digital converters, all, all of that running independent of each and every other antenna in that access point. So that’s your radio chain and your mimo systems are going to have multiple radio chains.

Meaning that each radio chain has its own antenna and power and everything else. So the mimo systems, then, we characterize them by the number of transmitters and receivers that they have by using the multiple radio chains.

8. MIMO Part4

So by using multiple transmitters, we’re trying to again spread out this data by using more than one antenna. In other words, trying to double everything we do. So what you’re seeing here, and the one that I just circled, would be three radio chains. And again, I have maybe a receiver or another sender with three radio chains. Now, what’s important here for you to see is that there is a thing called a two by three MIMO and a three by three. So what do we say in N? In 811 n we needed at least two antennas because if not, then you really haven’t accomplished 800 and 211. N so we might only have two radios that are going to transmit and maybe one of these radios is just to receive data. Maybe from somebody who’s backward compatible or not as good as 811 N. Or I could have all three of them doing the transmit and receive it’s as part of the negotiation. When you’re having a client connect to the actual network to determine how many radios that they are able to listen to at the same time. What they’re telling us though, is that on the receive side, when I have multiple receivers, it’s increasing the and R because of the tenant diversity. So that means that I just have even better quality communications.

9. MIMO Part5

So I’m sure you’ve already heard me say that mimo radios will transmit multiple signals. And a mimo radio can have the ability to send independent, unique data streams as well, which is good for those things that are backward compatible. Now, each independent data stream, whether I’m sending you two for my transmission or one it’s known as a spatial stream. And each unique stream can contain data that is different from the other streams that are being transmitted by one or more of the other radio chains. In fact, we hope that it is, because that’s where we’re getting the effective doubling of the bandwidth.

10. Spatial Multiplexing (SM) Part1

Again. I guess just kind of common sense. If I’m going to send multiple streams, then I’m sending you twice as much data. It’s just up to the receiver to figure out the order in which to put it all back together. So your mimo access point sending the two unique data streams to Memo client that hopefully will receive both streams, you effectively are doubling that throughput. Yes. If you add a third antenna and send all three to a receiver that can get all three simple math. You’re tripling that throughput.