CWNP CWNA – Very High Throughput (VHT) Part 2

8. 802.11ac Part7.

Now, the 256 qam was a big upgrade, and that came with eight or 211 AC. It doesn’t mean everybody is using it or that they can use it. But, you know, we originally with a eight or 211 A, had the 64 qam, and that gave us this great 56 megabits per second for speed, you know, identified 64 unique different values. And if you broke it up into the little square with the each corner having the number of bits we can send, we were able to send a lot of data.

So essentially what it does is it does a phase shift so that you can differentiate the eight different levels and also do an amplitude shift. Remember what those are? Phase shift was going from zero to 90 to 180 to 270. And then from there, you just change the amplitude to signal different types of values as far as the strength of the signal. And when you combine them together, you got these 64 unique values. Having that many values then gives you the ability to send that many more bits.

9. 802.11ac Part8

Now, again, 256 is going to be the highest modulation that we have already approved as a part of the amendment. It doesn’t mean that the actual hardware is capable of doing that, but in order for that to work, you also have to have a better S and R. In other words, it has to be a signal that is strong and can be heard, which means you have to be very close to the access point. As you get further away, that information is going to attenuate and you’re not going to be able to hear all of those at least your radio won’t be able to hear all of those subtle differences in the signal.

So even though we can go eight bits per sub carrier compared with six before, which is again as a big increase almost of one third or 33%, you still have to have a strong enough signal, which normally would have been saying, like I just mentioned a bit ago, being closer. Now, what can we do if we can’t get closer to the actual antenna? Well, the other thing was the antenna could focus that beam to get an increase in the dbis and to have a greater gain. And we’re going to see some of that as we talk about some of the beam forming options that you have with the AC.

10. 802.11ac Part9

Now, even though the amendment said that we can have a maximum of eight spatial streams, more than likely for a while anyway, your access points aren’t going to be able to support that. Right now they’re working just fine at four or four by four with the spatial streams, but it’s going to take another upgrade in hardware. So it’s kind of like I said a little bit ago, nice that we’re seeing some plans of what we can do. And now that technology has to catch up with those plans, very rarely does that happen anymore. So we’re going to have to make sure we have the right type of chipsets and not only on the access point, but yeah, on your laptops, on your mobile devices. They’re all going to have to be able to work with that. So right now, more than likely you’re going to see only four x four radios, which means that you’re going to be well under that almost seven gigabits per second of speed. And then again, that’s why they’re calling it the gigabit frequency for wireless communications.

Now right at the moment you’re going to probably see that they’ll easily support one by one or two by two. One of the reasons though, you might not see your portable devices go above two x two is that as you keep adding radios, I mean, think about it. The more electronic devices you’re adding in, it’s going to take more power. So you might have a problem with battery life, but if that’s okay with you or if it’s plugged in and you want that increased bandwidth, then it sounds like an option that maybe they can put into the actual hardware. But it does take more power. And by the way, wifi connectivity takes a lot more power than most everything else that’s on your laptop other than the brightness of your actual screen ring.

11. 802.11ac Part10

Now one of the things we can do is say, alright, I want great speed for just a single user so you can have what they call single user memo beam forming used to focus the signal to a client. Now this transmission should increase the level of the signal that the client receives because the idea here is that it’s going to focus that transmission, at least the antenna, to where it believes that the client is actually at.

So that’s more gain coming to that one client rather than going unidirectional and that gives them more distance and hopefully a higher throughput. But with AC you can support up to four different clients. And that just means that we’re going to try to again focus that beam towards those four clients with what we call the multi user mimo or the mu mimo. And again, it’s also depends on what the hardware is capable of doing.

12. 802.11ac Part11

So let’s take a look at the potential problems we have in today’s hardware. So here’s my access point. That’s doing 800 and 211 AC and it has a wired connection to a switch in today’s technology. We don’t really have a lot of high bandwidth coming in from the access point, so that connection is usually a gigabit interface.

But if you’re telling me now that I could have four, four users and all four of them with the multi user mimo connecting in here, even if it’s just at a gigabit each, that means I’m generating over here four gigabits of traffic and I’m trying to shove it into a one gigabit uplink. So we’re going to see some problems as this technology gets better about the aggregation and the delay, because we are oversubscribing a line. Now, when today’s most common switches at the Enterprise might have 210 gigabit ports, and I’m not saying you can’t use one of those ten gigabit ports, but the reason they’re there is because of the same problem.

All of your wired users are coming in at one gigabit and they need to have a ten gigabit port to go up to the next layer. So again, they don’t have an aggregation problem. So we are at least saying that we realized there could be some problems. Great. You can get up to the 160, can get up to the 256 qam, and with all of that speed, there’s your new choke point, the access point. It has a lot of data coming in, but it has no place to put it to be able to get it into the rest of the network. And so that’s something you have to consider. So when you think about the potential of what you can get, and this, by the way, even if I can get up to 600 megabits per second with 800 and 211 N, I’m still at that same problem. If I have a lot of people trying to communicate at that speed.

13. 802.11ac Part12

Alright, so again with AC, the things that are mandatory right now is that you well, it’s mandatory. everybody’s been doing 20 mhz channels, 811, and gave us the 40. So 80 is also mandatory to be able to support AC, but you can go up to 160. As far as the modulation encoding, we’re not going to see that 256 for a while. It’s optional spatial streams, one for clients, two for the access points, but we can go up to two to eight. The guard interval, again, is trying to help us in understanding how to protect the traffic to keep from having interference.

Mandatory 800 nanosecond. nanoseconds, by the way, it’s not milliseconds much shorter time versus a little bit shorter at 400. The options here of beam forming is going to be really cool as we talk about it. The spacetime block coding, the low density parity check, which we haven’t talked about, and the multi user that I already told you, can have up to four spatial streams. Those are optional, but not mandatory at this point. So that’s why I said here we have room for growth based on what the hardware is capable of doing for us.

14. Module 19 Review

Alright, so in this module we talked about the eight or 211 AC amendment, how it’s 5 ghz only, how we can bond channels up to 160 channel getting a huge amount of potential output or throughput. We also talked about how the qam modulation has improved, that they’re still using ofdm, but they’re using more of the sub carriers and sending more information with each one of those subcarriers. And then how with single user or multiuser we can help focus the antenna strength to get better distances, to get that better snr, to get better data rates and what the potentials are for the future.