Describe Wireless Physics

0:05Welcome to Describe Wireless Physics.

0:07And furthermore, welcome to the ENWLSD course.

0:11So we are setting off on a journey

0:13to start to explore wireless networking from a design

0:16perspective.

0:17Now, we might have a whole lot of different backgrounds here.

0:20Maybe we're trying to get the CCNP Enterprise,

0:23and we know that we need the ENCOR, the core exam,

0:25as well as a concentration exam.

0:27And so hey, this one qualifies.

0:30Maybe we can pass this exam as part of our CCNP journey.

0:33However, for other of us, we simply

0:35want to step into becoming a network architect.

0:37And part of that might mean that we need to better understand

0:40wireless design.

0:41And so maybe you have an extensive wireless background,

0:43and you've deployed and installed

0:45and managed and configured wireless networks.

0:48Or maybe you're more on the routing and switching side,

0:50and you've spent a lot of time in the IP and Ethernet world,

0:54and now you need a better understand

0:56design to just make us a better well-rounded design engineer.

1:01So whatever the background is, we're

1:02going to learn a whole lot about wireless,

1:04and again, especially focusing from a design perspective.

1:07Now, as far as this skill is concerned,

1:09you may already be scratching your head and saying,

1:11wait a second, Jeff, Describe Wireless Physics?

1:13I signed up to learn about Cisco wireless networking.

1:16Why are we having a physics lesson here?

1:18Well, because if we're going to be a well-rounded wireless

1:22engineer, and really, generally speaking,

1:24if we want to be really good at wireless networking,

1:27we need to understand how wireless communications work.

1:30And so before we dive into the blueprint of this exam, what

1:34we want to do is we want to take a look at making sure

1:36that we understand what wireless communication is

1:39from the ground up, starting with a physics lesson.

1:42So we need to understand what exactly light is,

1:45and why exactly we're talking about it, because Wi-Fi

1:48is light communications.

1:49We need to make sure that we understand

1:51what frequency and wavelength are because we're

1:53going to be talking extensively about frequency

1:55and wavelength throughout this course.

1:59Don't worry.

1:59We're going to be relating this constantly back to Wi-Fi

2:01to make sure that we're staying grounded,

2:03because, yes, it's great to learn the wave particle

2:06duality of light, right?

2:07I mean, who wouldn't want to know that.

2:09It's a great party trick to start

2:10to talk about E equals mc squared

2:13and what the constant c stands for and such.

2:16But at the same time, if we're not relating this back

2:19to why it matters and why Wi-Fi designs need

2:22to consider all of this, well, then, we're

2:24not doing ourselves any favors.

2:26So all that to say, let's go ahead and dive

2:28into this physics lesson to make sure

2:30that we understand what Wi-Fi communication even is

2:32and what this wave particle duality concept is,

2:36but how that starts to affect our wireless design,

2:38especially as we dive into things like wireless frequency

2:40and wavelengths.

2:41So with that, I will see you in the next video.

0:05This conversation around the physics of light

0:07is giving me some serious flashbacks

0:09because I studied this extensively

0:10in my university experience.

0:12I didn't actually go to get a degree in IT,

0:14just sort of ended up here.

0:16In fact, my understanding of Wi-Fi

0:19is actually what got me into IT.

0:21Because I started as a wireless installer, which quickly

0:25led to me doing wireless designs very shortly out of college.

0:28And so as we start talking about all

0:30of these different concepts of physics and light waves

0:32and everything like that, we do need

0:34to understand that there is a connection

0:35to our Wi-Fi networks.

0:37We need to be able to do site surveys, where we're

0:39looking at a room and saying, OK, I

0:42understand what the light waves are going to do here.

0:44I understand how they're going to propagate down a hallway,

0:46or how they're going to be maybe absorbed

0:48by different types of materials into my environment.

0:50And so the more I understand about light from a physics

0:53perspective, the better I'm going

0:54to be at performing some of these site surveys.

0:56So let's go ahead and dive in and start

0:58to talk a little bit about the physical nature of light.

1:01All right, so first of all, why are we even talking about light

1:04at all?

1:04Well, it might come as a surprise to some of us,

1:07but when we're talking about wireless communications

1:09like Wi-Fi, this is using light in order to communicate.

1:12And while we can't just look at a Wi-Fi device

1:15and see it blinking, that's effectively what it's doing.

1:18However, in this case, it's actually using a range of light

1:21that cannot be seen by the human eye.

1:24And so once again, I could look up at the access point,

1:26and aside from maybe a status LED,

1:28I'm not actually going to see the light that's

1:30being emitted by that device.

1:32And so when we think about wireless communication,

1:34we need to start realizing that if I'm

1:37going to transmit from this dot on the left, I suppose,

1:40and receive from the device or dot here on the right

1:42that we're going to be transmitting using light waves.

1:46And so everything that we think about, from, hey,

1:48how is this light wave going to propagate,

1:51how is the signal going to get absorbed by the environment,

1:54all of this comes back to the fact

1:55that it is actually light waves that are being transmitted.

1:59Now, if you've ever taken any physics courses in high school

2:01or college, you may have found that you

2:03needed to ask a very important question, which

2:06is, what exactly is light?

2:08And I'm going to tell you right now that this

2:10is a question that physicists have been trying to figure out

2:14in greater detail over the last several hundred years.

2:17And the conclusion, as best we can tell today,

2:19is that light is sort of like a wave.

2:22It sometimes behaves that way.

2:24But it's also sort of a particle.

2:27You think of a particle as something solid.

2:29A little ball, for example, that's

2:31being flung across the room-- you could call that a particle.

2:33And so is it a wave, or is it a particle?

2:36And the answer from a physics perspective

2:38is it's actually both.

2:40This is what we call the wave particle duality theory.

2:43And as fancy as this phrase sounds,

2:45it really is just saying that there

2:46is a dual nature to light.

2:48It's running in two different fashions.

2:50We have the wave side of it, and we

2:52have the particle side of it.

2:54So it's behaving like both of them,

2:55just depending on the situation.

2:57A lot of this understanding comes back to,

2:59believe it or not, the late 1800s and the early 1900s.

3:03This is when a lot of this discovery was taking place.

3:06We might know some of the scientists who were involved.

3:09Probably a lot of us know who Einstein is.

3:12But then we also talk about Maxwell Planck, as well as

3:15Niels Bohr.

3:16And there are a couple of very famous experiments

3:18that ended up explaining this dual nature to light.

3:21First of all, we had the double slit experiment.

3:24The double slit simply proved that light behaves like a wave.

3:28And so this is to demonstrate the wave nature of light.

3:31This experiment allows us to shine light waves

3:34through-- we'll call it a barrier--

3:35a paper, what have you, that has two slits

3:37in it, one here and one here.

3:40And the result is that we actually

3:41see that light comes through in waves in such a way

3:44that we start to see them interfering with one another

3:46here.

3:47And this results in a pattern that

3:49looks in a specific fashion that more or less proves

3:52that this is what's happening, that light

3:54is behaving like waves.

3:56And for a long time in the physics world,

3:58because of this experiment, it was well

4:00thought of that light was simply waves.

4:03However, eventually we realized that there

4:04is another problem that we needed to solve,

4:06which is known as the photoelectric effect.

4:09The photoelectric effect says that if I'm

4:11going to shine light onto a metal plate

4:13that there's going to be some number of electrons that

4:16are emitted as a result. And the amount

4:18of electrons that are emitted actually

4:20has to do with the frequency of the light.

4:22And what was ultimately concluded

4:24is that the amount of energy that

4:26was being absorbed by the plate and converted into electrons

4:29being emitted was actually being absorbed

4:31in discrete quantities.

4:33Now, if light was purely 100% waves,

4:35then we wouldn't ever see anything discrete

4:37happening here because this is an analog signal.

4:39And so as a little bit is absorbed,

4:41we'd fire off electrons, so to speak.

4:43But this discrete nature actually

4:45tells us that light is also behaving like actual particles.

4:49And so this is an experiment that was run by Einstein.

4:52And by the way, this actually won him the Physics Nobel Prize

4:55in 1921.

4:57And so this was a very big deal in discovering

4:59that light actually can behave as both,

5:02both as waves and as particles.

5:04Now, the last thing I want to talk about

5:06as far as the physics of light is concerned

5:07would be the speed of light.

5:10Light is not actually instantaneous.

5:11It's like when we talked about up here,

5:13how we said that light is being propagated

5:15across this distance.

5:17And furthermore, the speed of light

5:18is what's known as a constant, meaning that it never

5:21changes, at least as far as when it's in a vacuum,

5:24when nothing is impeding it.

5:25This constant is known as c.

5:27And it actually shows up in that famous Einstein equation,

5:30E equals mc squared.

5:32This c right here is actually the speed of light.

5:34So it's energy is equal to mass times

5:36the speed of light squared is what this relationship is

5:39describing.

5:40And so this value of c has been extensively measured,

5:43especially now in our modern era with all of the fancy equipment

5:46that we have.

5:47And we've got it down pretty well.

5:49I'm just going to round here, but essentially, it

5:51comes down to being 2.99 times 10 to the eighth meters

5:55per second.

5:56This is very, very fast.

5:58This is why, from the human eye perspective,

6:00we can never detect that light is

6:02moving over the course of time.

6:04However, if we stretch it out across great distances,

6:06we start to see this come to life.

6:08Because if I'm going to look at the sun, for example,

6:11it actually takes eight minutes for the light

6:14to get from the sun to the Earth.

6:16And so we could often joke, if I'm looking at the sun,

6:19the sun could have exploded five minutes ago

6:21and I'm not going to know because the light showing

6:24the explosion is still only halfway to Earth.

6:27And so it's sort of a funny little concept to say,

6:29hey, we're looking back in time, what

6:31we're seeing is what was happening on the sun

6:33eight minutes ago.

6:34Now, we can stretch it out even further

6:35to say that, hey, we've got the nearest star is

6:38what's known as Alpha Centauri.

6:39And technically, it's a cluster of three stars.

6:41But either way, we've got three stars

6:43out here that are so far away that it actually

6:46takes four years for the light to get to us.

6:49And I know.

6:50I drew the arrow a little bit backwards here.

6:52The light's coming from Alpha Centauri to Earth.

6:55And so when I look up at the night sky

6:56and I see Alpha Centauri out there,

6:58that light is four years old.

7:00And the reason why it takes so long for the light to get here

7:03is because it's actually about 93 million miles away.

7:07Or for those who measure in kilometers,

7:08we're talking about 150 million kilometers.

7:11This is where we get that other measurement of distance.

7:13We talk about miles and kilometers,

7:15but we also talk about the concept of the light year.

7:18When we talk about a light year, it

7:19sounds like a measure of time because year

7:21is a measure of time.

7:22However, the light year is talking about distance.

7:25It's the distance that the light can go in a single year.

7:29And so Alpha Centauri is four light years away-- really,

7:32about 4.3, 4.35, something like that.

7:34But we'll cover astronomy in another session.

7:37Either way, we're talking about four light years away.

7:39That's a distance of measurement between Earth and the nearest

7:43star.

7:43Now, one thing to keep in mind in all of this

7:45is that this speed of light right here, yes, it's

7:48a constant, meaning it's always this fast.

7:50But at the same time, it is affected by the medium.

7:53And when I say medium, what I mean

7:55is if it goes through air, for example,

7:58or it goes through water or it goes through a material,

8:01it's going to get slowed down.

8:03This is the speed in a vacuum, meaning nothing is impeding it.

8:07And so we should keep that in mind as well.

8:08So this is wonderful and all, but let's bring this back

8:11to the idea of Wi-Fi.

8:12Why are we talking about all of this physics of light

8:15when we're really here to learn about Wi-Fi and wireless

8:18networking?

8:19Well, as far as Wi-Fi is concerned,

8:21we are primarily going to be focusing

8:22on the wave nature of light.

8:24And so everything we talked about over here,

8:27as far as the double slit experiment and the fact

8:29that it does behave like a wave, this is very important.

8:31If we don't understand this, we're

8:33going to have a hard time being wireless design engineers.

8:36The wave nature of light is going

8:38to lead to conversations around frequency and wavelength,

8:41which are extremely important concepts when it comes

8:44to doing our wireless site surveys

8:45and understanding what we're looking for when we're talking

8:48about interference and possibly materials that

8:50might absorb wireless signals.

8:52This is going to help us understand

8:53how light waves propagate because if we're

8:56going to install, for example, two wireless bridges, well,

8:59wireless bridges over the course of a great distance.

9:01And this can be affected, for example,

9:03by the curvature of the Earth.

9:05And it can be affected by the fact

9:08that Wi-Fi is not a direct line of sight concept.

9:10If I have a bridge on this side and a bridge on this side,

9:13Wi-Fi signal does not look like that.

9:15That would be wonderful if it did.

9:17But really, it's looking like this.

9:19And so we know that we've got waves, which actually creates

9:22quite a larger boundary of space where those Wi-Fi waves are

9:26going to exist.

9:27And so this has to do with Fresnel Zone concept

9:30that we're going to have to study if we want

9:32to deploy wireless bridging.

9:33So just a little teaser there for when that comes up.

9:35Now, the speed of light isn't going

9:37to really affect us that much.

9:38This is something that's fun to know.

9:40However, I will say this.

9:41As far as optical networking is concerned, keep in mind,

9:44optical networking relies on the speed of light as well.

9:47And if I were to take the distance between New York

9:49and London, that's a distance of about 3,500 miles.

9:53Well, the speed of light can only

9:55travel from New York to London so fast, right?

9:57And so at that point, we're looking

9:59at about 18 milliseconds that that light

10:02is going to take to travel from one side to the other.

10:04Now, while that's not perceptible from a human eye

10:07perspective, going through fiber optic communications,

10:10the theoretical lowest amount of latency we can ever get

10:14is 18 milliseconds one way.

10:16And so there's not going to be such a thing as communicating

10:19between New York and London at 5 milliseconds

10:21because light can't go that fast unless we come up

10:24with some crazy technology that teleports

10:26light or something along those lines,

10:27which, hey, maybe they're working on.

10:29Who knows?

10:29But either way, the more we understand

10:31about light, the better network and especially wireless design

10:35engineers we're going to be.

10:36All right, so I don't know about you,

10:38but I love having these types of conversations.

10:40Physics is just a really entertaining subject for me.

10:43But either way, just a quick synopsis.

10:44First of all, light operates both as waves and as particles.

10:48And so we've got this wave particle duality concept

10:52that we should understand.

10:53But as far as Wi-Fi is concerned,

10:54we're definitely going to focus more on the wave

10:56nature of light communications.

10:58Now, light also has a constant speed when in a vacuum.

11:02This is that lowercase c.

11:03We see this in some famous physics equations,

11:06like E equals mc squared.

11:07And the velocity is 2.99 times 10 to the eighth meters

11:11per second.

11:12I don't think Cisco's ever going to ask us that on an exam,

11:14but it creates some fun scenarios

11:16like we talked about with the optical networking concept.

11:18And so from a wireless networking perspective--

11:20I already said it, but I'll say it again--

11:22our focus is going to be on the wave nature.

11:24We're going to go into a little bit more specifics here

11:27around just starting to study waves and waveforms

11:30and what that means for us because eventually, we're

11:33going to start talking about Wi-Fi interference

11:35and doing our site surveys and understanding absorption

11:38and refraction.

11:40And all of these concepts come back to the fact

11:42that light is going to operate, yes, as a particle,

11:45but also as waves.

11:46I hope this has been informative for you,

11:48and I'd like to thank you for viewing.

0:05All right, so now that we understand a little bit more

0:07about how light behaves from a physics perspective,

0:09it's time to start analyzing waveforms.

0:11We are going to need to understand

0:13these concepts of waveforms, as well

0:15as the frequency and the wavelength

0:16and some of the terminology that we're

0:18going to be studying in this video in order

0:20to properly understand wireless propagation.

0:22Let's take a look.

0:23All right, so when we are drawing out waves like this,

0:26this is known as a waveform.

0:28Waveforms can be applied to pretty much anything.

0:30And we think about light waves, which

0:32is going to be the focus of this conversation,

0:34because once again, Wi-Fi communication uses light waves.

0:38However, it can also apply to things

0:40like sound waves and water waves,

0:42and for that matter, jump ropes.

0:44A lot of physics teachers will use jump ropes

0:46to demonstrate the qualities of waves.

0:49Now there are a lot of different types of waveforms.

0:51For example, we've got square waves and triangle waves.

0:55However, when we have these nice curves,

0:57we usually call this a sine wave,

0:59or maybe a sinusoidal wave.

1:00So at this point, we need to start learning

1:02the anatomy of this waveform.

1:04For example, we have the crest of the wave.

1:06That would be right here, the highest point of the wave.

1:09Now, conversely, we have the trough of the wave.

1:12And the trough is going to be down here.

1:13And yes, that is actually how you spell it in English.

1:16Don't ask me why.

1:17But hey, that is how you spell "trough".

1:20Now, if we were to draw a line right

1:21through the middle of this waveform,

1:23we can call this the origin.

1:24And every now and again, you might hear something other

1:27than origin, like the 0 amplitude or possibly

1:30the resting point.

1:31But origin is usually what we're going to call this.

1:34And so the idea here from the beginning

1:35is that we're going to rise above the origin a certain way,

1:39come back down, hit the origin again, go below the origin,

1:42come back up.

1:43And the path that I just drew here--

1:44let me draw it a little bit thicker.

1:46This right here is a single wave on this waveform.

1:50We start at the exact same point, so for example,

1:52here on the origin.

1:53And we end over here, also on the origin.

1:56Now, I can also take a single wave from another point.

1:59For example, I could start all the way at the crest up here.

2:02And I could come down and all the way back up.

2:04And this also represents a single wave

2:06because I start from one spot, and when

2:09I get back to that same spot at the other end of the cycle,

2:12then, hey, at that point, once again, this is a single wave.

2:15Now, the amount of time that it took

2:17for me to complete a specific wave, this

2:19is known as the period.

2:22And so we measure the period in seconds.

2:24And lastly, from a terminology perspective,

2:26we also need to concern ourselves with the amplitude.

2:30Now, the amplitude is going to describe how far off of origin

2:33the waveform goes.

2:35But it's only in one direction.

2:36We don't measure amplitude, for example,

2:38from the crest down to the trough.

2:40That's not the amplitude.

2:42Instead, the amplitude is simply from the crest to origin.

2:45Or hey, we can measure it the other way.

2:47We can measure it from origin down to the trough.

2:50Now there is one other key point of terminology

2:52before we get into maybe the most important ones, which

2:54are frequency and wavelength, but we want to mention phase.

2:58The idea of phase is to indicate where, at what point,

3:02do we really start this process right here?

3:05Because given this waveform, I could start it right here

3:08at this moment in time, or hey, I

3:10could also start it right here and do the exact same waveform,

3:14but it's just off by a little bit.

3:16And so what we can end up with is a waveform

3:19that's actually exactly out of phase of the first waveform.

3:22And at that point, what we're talking about

3:24is it's basically just going to be exactly backwards

3:26relative to it.

3:27So all of my crests should line up with troughs and vice versa.

3:30And that's not the prettiest waveform.

3:32But hey, we'll take it.

3:34So for example, again, my crest winds up with the trough

3:37here and vice versa.

3:38My crest lines up with the trough.

3:40And yes, I know it's not exactly right.

3:42But we do see that this is perfectly

3:44out of phase with one another.

3:45And so we might call this 180 degrees out of phase, or maybe

3:49negative 180 degrees, however we want to describe it.

3:52And so this will come up in our conversations

3:54around interference as well.

3:56So keep that in mind.

3:57So now the big ones.

3:58First of all frequency.

4:00We talk a lot about frequency in our wireless communications.

4:04For example, we talk about the 2.4 gigahertz spectrum

4:08and the 5 gigahertz spectrum.

4:10And when we're talking about frequency,

4:12this concept of hertz, this is going to tell us

4:15how much the frequency is.

4:17So what exactly is frequency?

4:19Well, it's the number of modulations

4:21or the number of waves that we get in a specific time period.

4:25And so we take the number of waves--

4:27it's truly a number--

4:28and we divide it by time.

4:30And we're going to measure this using

4:32a quantity known as hertz.

4:34And yeah, that's somebody's last name.

4:36So it's not saying I'm going to hurt you--

4:38I'm going to "Hertz" you, I suppose.

4:39But we are going to measure it in this,

4:41and we abbreviate it with a big H And a little z.

4:44The funny thing about hertz is effectively

4:46it is representative of 1 over second.

4:49So it's actually measuring a number

4:51of occurrences per second.

4:53And so seconds here, that is our frame of reference.

4:56Now, typically, we're going to represent frequency

4:59as sort of a curly f.

5:00Every now and again, you might see it

5:02represented by the Greek letter nu, which kind of looks

5:04like a v. And especially this is going

5:06to be the case in physics circles.

5:07I'm going to come over to my pink waveform here,

5:09and I'm going to measure out, let's just say, 1 second.

5:12So let's just say that this is about 1 second in time.

5:15And then I'm going to count how many waveforms

5:17happened in that time period.

5:18And so here's one waveform right here.

5:21Remember, we've got to start at the same spot

5:23and end at the same spot.

5:24So there's one waveform.

5:25Here's another waveform.

5:27So that's two.

5:27Here's another waveform.

5:28That's three.

5:29And so assuming that lines up perfectly with 1 second,

5:32we would say that this waveform has a frequency of 3

5:37hertz, three waves per second.

5:40And so when you extrapolate this out,

5:41if we have a single wave in a second,

5:43well, that would be 1 hertz.

5:45And it sounds weird to say 1 hertz because it sounds

5:47like it's plural, but it's not.

5:49Again, it's somebody's last name.

5:51So 1 hertz would be one per second.

5:53Now, if we were to do 1,000 waves, 1,000

5:56cycles in a single second, this would

5:58be known as a kilohertz, "kilo" meaning 1,000.

6:02And so we should be familiar with that

6:03in the networking world, kilobits per second and such.

6:06And so we are familiar with equating it to 1,000.

6:09But then we start to get into more interesting ranges.

6:11Because if I say a million cycles per second,

6:15well, now we're talking about 1 megahertz.

6:18And lastly, if I say a billion, I'll just say 1B here,

6:211 billion waves in a single second,

6:24well, now we're talking about gigahertz,

6:26which should start to sound a little bit more familiar,

6:29especially since we just set it up here.

6:31Our Wi-Fi communications are happening in the 2.4 and 5

6:34and even now the 6 gigahertz bands.

6:36And therefore, we're talking about a billion

6:39of these waveforms occurring within a single second.

6:42And that is absolutely incredible,

6:44at least it is to me.

6:45I'm pretty impressed by that.

6:47Now, the other big concept, which

6:48is actually the inverse of frequency,

6:50is the concept of the wavelength.

6:53Whereas the frequency measures the amount

6:54of waves over the course of time,

6:56the wavelength is going to actually measure

6:59the actual physical distance of the wave itself.

7:03So what I mean by that is coming back to-- let's

7:05just look at this waveform right here.

7:07So I'm trying to kind of chop it off there.

7:09So we've got a single waveform.

7:10We're going to measure from here to here,

7:13and that's going to be a physical distance.

7:16Now, for most of our conversations,

7:18this physical distance is going to be pretty small.

7:20So maybe it's in the nanometer range.

7:23That would be one-billionth of a meter.

7:25And for that matter, we might even

7:27be talking about a picometer, which

7:28is a trillionth of a meter.

7:30However, our waveforms can actually be quite long as well.

7:33We might actually be talking about actual meters

7:36when it comes to our waveforms.

7:37Or we can talk about millimeters.

7:39So at least at that point, we're talking

7:40about thousandths of a meter and something we can visualize,

7:43rather than something like a micrometer or a nanometer.

7:46And so that's really, just to flesh this all out,

7:48we've got meters, millimeters, micrometers, nanometers,

7:52and picometers.

7:53Now, wavelength is represented by the Greek letter lambda.

7:56It sort of looks like this.

7:57I believe it was chosen because it actually looks sort

8:00of like a wave, doesn't it?

8:01And what we're going to find is that as frequency increases,

8:04our wavelength is going to decrease and vice versa.

8:06If frequency decreases, then our wavelength

8:09is going to increase.

8:10They are actually directly related to one

8:12another via a specific equation that's

8:15going to involve, guess what, the speed of light,

8:17that constant c that we already talked about.

8:20The reason why is because this light wave

8:22is propagating at the speed of light.

8:24And so the distance that it's covering here

8:26is relative to that speed.

8:27And that's why this constant is going to bind our two

8:30concepts together.

8:31And so the equation here is c is equal to our wavelength

8:35times our frequency.

8:36And this relationship should make sense

8:38because if I draw a waveform that looks like this, well,

8:41that has a very high frequency.

8:43We've got 5 waveforms.

8:45Let's say that's in a second.

8:46So maybe this is a full second.

8:48There's five waveforms in there.

8:49And our wavelength right here, that measurement is very small.

8:54Now conversely, if I draw a very long wavelength,

8:58and so maybe this is 1 second as well,

9:00well, now I'm not even barely at-- what is that?

9:03About 1 and 1/2 maybe of hertz?

9:05And so frequency is a lot lower, and therefore

9:08my wavelength from here to here is much greater.

9:11This is why they're inversely proportional to one another.

9:13And so it's important to start to understand

9:15that relationship as we get deeper

9:17into Wi-Fi communications.

9:19So coming out of this conversation,

9:20we should have a good comfort level around the anatomy

9:23of the waveform.

9:23We should know what the crest is and the trough and the period

9:26and the amplitude.

9:27And we should be able to identify what these

9:29are given a specific waveform.

9:31Now, beyond those concepts, we have these two big ones,

9:33the first of which is frequency.

9:35Frequency is measuring how many waves are

9:37on this waveform per second.

9:39And we measure that in hertz.

9:40Hertz literally is just a per second type of measurement.

9:44And so if we have 1,000 waves all crammed

9:47into this waveform in a single second, well,

9:49that's going to be 1 kilohertz.

9:51Now, inverse to the frequency is the wavelength.

9:53And so the more waves that we cram into 1 second,

9:56the shorter those waves are going to have to be.

9:58And that would be the wavelength measurement.

10:00And so we just need to understand

10:02this inverse relationship.

10:03We don't necessarily have to have memorized, especially

10:05for this exam, that the speed of light

10:07is equal to wavelength times frequency.

10:09It's more just understanding that as frequency goes up,

10:12wavelength size has to go down and vice

10:13versa because that c on the other side of the equation

10:16is a constant.

10:17It never changes.

10:18And so if we do increase frequency,

10:20we will expect to see wavelength go down and vice versa.

10:22I hope this has been informative for you,

10:24and I'd like to thank you for viewing.

0:00[MUSIC PLAYING]

0:05I don't know about you, but for me, I just absolutely

0:07love a splendid sunset.

0:09Seeing all the different colors of the rainbow

0:11right there at the horizon stretching up

0:13from this bright red at the horizon

0:16to sometimes even see the oranges and the greens

0:18and then the blue of the atmosphere.

0:21And so as beautiful as that is, we

0:23can actually start to break that down into physics level

0:26conversations about what's happening,

0:28because every different color that we see

0:30is a different frequency of light.

0:32And there's an entire spectrum of light

0:35out there that the human eye can't even see.

0:37And so what we're going to do in this video is we're going

0:39to talk about this electromagnetic spectrum,

0:42we're going to understand the visible range of light that we

0:45see, but then also all of the light that we can't see,

0:48which is very important because our wireless communications,

0:50as we've already mentioned, is using light we cannot see.

0:53Let's dive in.

0:54For most of us humans, we're going

0:55to see a pretty wide range of colors.

0:58And so we see, for example, red and orange and yellow.

1:02And if you grew up English speaking,

1:04you probably learned about this concept of ROYGBIV,

1:06although I think they've gotten rid of the I now

1:08and it's just blue and violet, and we kind of

1:10got rid of indigo because we never really knew

1:12what indigo was anyways.

1:14But either way, we've got this a range of colors that

1:17is described as a spectrum.

1:19The reason why we call it a spectrum

1:21is because it's analog.

1:22We don't really know where red ends and orange begins.

1:25We just sort of see the colors blend together

1:27as we look into the sky, again looking at a rainbow

1:31or possibly looking at the sunset or maybe a reflection

1:34in the water or whatever it is that we're seeing.

1:36Now the reason we have this beautiful spectrum

1:39is because our eyes are actually equating

1:41each different frequency of light with a specific color.

1:45And so when we look at the spectrum,

1:46really what it's arranged by is it's arranged by frequency.

1:50And so we have an increasing level

1:51of frequency on the spectrum.

1:53So red would actually be the lowest frequency

1:57within the visible spectrum of light.

1:59And then violet is going to be the highest frequency

2:01that we can see.

2:02And naturally, we can see everything in between.

2:04So orange and yellow and green and blue,

2:06these all show up, even though they're

2:08in the middle of the range, so to speak.

2:10Well, this is well and good, other than

2:12that this spectrum, the visible spectrum

2:14is just a tiny sliver of the overall spectrum of light

2:18that exists.

2:19And what we find is that we've got a whole lot of light

2:21at lower frequencies we can't see,

2:23and then we've got light at higher frequencies

2:25we can't see.

2:26And we call this the electromagnetic spectrum.

2:29Now just like with the visible spectrum

2:30how red blends into orange, this electromagnetic spectrum,

2:34this is also an analog concept.

2:36And so we've got every single range of frequency

2:38possible all the way from very low to very, very high.

2:41But in order to simplify our lives a little bit,

2:44we just grouped a lot of these frequencies

2:45together into what we call different regions.

2:48Now the regions right around the visible spectrum

2:51are actually appropriately named,

2:52because this first region to the left, this is called infrared.

2:56And we look at the root word infra, it means below.

2:59So we're truly talking about light frequency

3:01that is just below red.

3:02Now on the other side, we have this light range

3:04that we call ultraviolet, because the root word

3:08ultra actually implies above or beyond.

3:11And so we've gone beyond violet, we're

3:13talking about ultraviolet light.

3:14And so here we sometimes call this UV light,

3:16it's the light that we often talk about as

3:19far as the sun is concerned.

3:20And sometimes we just need to make

3:22sure that we're protecting our skin with sunscreen

3:24because we don't want too much UV or ultraviolet light.

3:27Now the other regions down here on the left,

3:29these are called radiowaves and microwaves.

3:33And then the regions on the right, we have X-rays

3:35and we have gamma rays.

3:37So what are these different frequencies look like?

3:40Well, radiowaves are going to be really

3:41in the realm of kilohertz for the most part.

3:43If we hear that we're talking about kilohertz,

3:45that probably is going to be the radiowaves

3:48that we use, for example, to send radio and TV

3:51broadcasts in the air.

3:52Then we enter into the microwave realm, which yes, this is where

3:55our kitchen microwaves operate.

3:57But more than that, it's where our networking devices operate

4:00and our cell towers operate.

4:01We're usually talking more in the megahertz

4:04to gigahertz range when it comes to our microwave

4:06communications.

4:08And then once we start getting into the terahertz range,

4:10this is when we're talking about infrared.

4:13Now by the time we get to ultraviolet,

4:15we can no longer really use mega, giga, terra

4:18because we've really gone beyond some of those words.

4:21And so ultraviolet, for example, we're talking about maybe a 10

4:23to the 15 kind of concept here as far as Hertz is concerned.

4:27We're talking about X-rays, you might hear something like 10

4:29to the 18th and 10 to the 21st for gamma rays.

4:32But keep in mind that we also have to cover the full range.

4:35And so 10 to the 19th power also exists

4:38within this discrete X-ray region.

4:40And so these are estimations that we can use.

4:42However, we're not really trying to lock this down

4:44to memorize where microwaves and an infrared begins

4:49and that kind of thing.

4:50Instead, mostly what we care about are down here.

4:53Hearing kilohertz, megahertz, and gigahertz

4:55should clue us in to what type of communications

4:57we're talking about.

4:58Now something we find, especially

5:00as we analyze this range of the electromagnetic spectrum, which

5:04is really where we use light for communications, what we start

5:07to see is that the higher the frequency that we have,

5:11it's going to end up meaning that our distance that's

5:14traveled with the same amount of energy goes down.

5:18This happens for a few reasons.

5:19First of all, light is going to lose energy

5:22across what we'd call free space propagation.

5:25Well, probably more importantly as frequency increases,

5:28our ability to pass through materials is going to go down.

5:33For example, a brick wall is going

5:36to absorb higher frequencies a whole lot easier than it's

5:39going to be able to absorb lower frequencies.

5:42For example, when we think about TV and radio broadcasts,

5:45what do we think about?

5:46We think about a TV station that's

5:48probably miles away from us.

5:50We don't need to be within a half mile of the TV station

5:54in order to get that signal.

5:55We also expect it to pass through walls,

5:57because my TV antenna, I mean, yes, I

6:00can stick it up into the sky and that

6:01will get me a better reception.

6:03However, a lot of times, it's going to pass through my walls

6:05and get right to my TV.

6:07And so we compare this type of wireless communication

6:10with a different type of wireless communication,

6:12such as, well, let's just talk about cellular.

6:15Cellular is best when I'm maybe within, well,

6:17let's just say one mile of a cellular tower.

6:20And a lot of times, I know if I step inside my house,

6:23for example, my signal is actually going to go down,

6:26because the cellular signal is absorbed a whole lot more

6:28by my walls and my insulation.

6:31And so forget it, if I go into the basement,

6:34then I'm not going to get any amount of cellular signal

6:37because those waveforms are getting absorbed before they

6:40ever get to my cell phone.

6:41And lastly, we look at Wi-Fi.

6:43Wi-Fi is a higher frequency than cellular.

6:45And so when we're talking about Wi-Fi, I mean,

6:48I'd love to be able to get a Wi-Fi signal one mile away.

6:51But oftentimes, I can't even get across my house

6:54with a Wi-Fi signal.

6:56And that's just because we're using a much higher frequency.

6:59So sometimes my walls inside my house

7:01actually will absorb the Wi-Fi signal,

7:03even though I only have one wall between me

7:06and the access point.

7:07And furthermore, by the way, we are

7:08going to find, especially in our wireless designs

7:11that 2.4 gigahertz actually performs a whole lot better

7:14than five gigahertz.

7:16So I'm not by any stretch saying that we

7:18should be designing inside the 2.4 gigahertz

7:21spectrum because we should not these days.

7:23But one of the ramifications of that is my access points

7:26aren't going to go nearly as far in this five gigahertz

7:28spectrum.

7:29And so especially if I'm deploying

7:31two different frequencies and I'm

7:33supposed to be designing around these two different frequencies

7:35for some reason, that's going to make my wireless

7:38designs really tricky because an access point here

7:41will have a range that it can reach for the five gigahertz

7:43spectrum, but I'll have a much larger range

7:45that can reach for the 2.4.

7:47And so I either need to turn down the power of the 2.4

7:50gigahertz radio in order to match the five gigahertz range,

7:53or I need to otherwise be very, very careful

7:56in my wireless designs, even though again, this example

7:58I don't expect to encounter this very often,

8:01but it is an interesting side effect to this whole frequency

8:04and distance conversation.

8:05Now, one last thing to consider as far as light frequency is

8:08concerned would be the safety to people running

8:12this type of technology.

8:13What we find as we look at light and frequency

8:15is as light increases in frequency,

8:18it actually starts to become very

8:19dangerous to the human body.

8:21The reason for this is because our light waves,

8:23our wavelengths are so small is why we're talking about maybe

8:27picometers or smaller, they can actually

8:30break into human cells.

8:31And once they break into human cells,

8:33they start to break down our chromosomes

8:36and start to result in mutations, and this results

8:39in some very bad situations.

8:41This is why the medical world is very careful around x-rays,

8:44even though it's very beneficial to us

8:46from a medical perspective to get an x,

8:48they have to track how many X-rays that we've

8:51exposed ourselves to recently because the more X-rays

8:54that we get, the more we're placing ourselves in danger.

8:57And by the way, this is why when I go to get an X-ray, yeah,

9:00they have to push it right up against me

9:02because it's got to be really, really close for the distance.

9:05But this is also--

9:06this machine right here, I suppose, the X-ray machine.

9:08But there's also why the person who's administrating the X-ray,

9:12they run behind a lead wall to make sure

9:16that they're not exposing themselves to X-rays as part

9:18of their day-to-day job.

9:19So the reason I bring this up is because the lower frequencies

9:23are considered to be very safe.

9:24So when we're talking about lower frequencies,

9:26we're talking about this entire spectrum down here.

9:29In theory, all of this frequency is a whole lot safer even

9:33than the visible spectrum, which is sitting right in the middle.

9:36So if ROYGBIV type of lighting isn't

9:38causing us any kind of health issues,

9:41then none of the frequencies down here

9:43should be causing us health issues either.

9:45Now there have been a lot of studies out there that have,

9:48some of them are leave us skeptical maybe

9:50about the health implications of some of this.

9:53It also certainly matters how close

9:55we are to access points and even our cell phones and such.

9:58But all that to say, one of the reasons

10:00why we are deploying our cellular and Wi-Fi

10:03communications into this range is in order

10:06to keep us all safe.

10:07So hopefully, that places our minds a little bit at ease,

10:10but also maybe we need to place other people's mind at ease.

10:13As a wireless design expert, we can

10:15point to the electromagnetic spectrum

10:17to assure everyone around us why we consider

10:20this technology to be safe.

10:22So as we break down this conversation

10:24of light and physics, we do find that when

10:26we're looking at different colors,

10:28that represents different frequencies to our eyes.

10:30And so when we look at the visible range of light,

10:33we see it range from red at low frequencies

10:35to violet at high frequencies.

10:38Now that's just a very small part

10:39of the overall electromagnetic spectrum.

10:42The electromagnetic spectrum goes way lower frequencies

10:45than we can see and way higher frequencies that we can see.

10:47This is why we can't see our Wi-Fi devices

10:49talking to each other, because they're

10:51communicating at a range that is too low of a frequency for us

10:55to see.

10:55And so the higher the frequency we also find,

10:58the shorter distances that we can go

11:00with the same amount of energy.

11:02And so this is why TV and radio broadcasts can go so far,

11:06and cellular towers can go not quite as far, but still pretty

11:09far, and our wireless device might

11:11be on the other side of that wall,

11:12and I'm not getting a good signal.

11:14And so understanding light frequency

11:16and understanding how that affects

11:18our distances and our propagation,

11:20as you can imagine, this is going

11:21to matter a whole lot when we start doing our wireless site

11:24surveys.

11:24I hope this has been informative for you,

11:26and I'd like to thank you for viewing.

0:00[MUSIC PLAYING]

0:05All right, we said at the start of this

0:07that if we're just going to have a physics lesson, then that's

0:10kind of fun, I suppose, but it's not

0:12going to make me a better Wi-Fi engineer.

0:14Now it's time to take all of the lessons

0:15that we've been learning and actually apply it

0:17to wireless communications.

0:19So in this video, we're going to start

0:20to introduce these concepts of interference, for example,

0:23as well as the different frequencies that we might

0:25deploy in a wireless network and start to talk about these bands

0:28and the unlicensed and the licensed spectrum.

0:30So let's just go ahead and dive in and cover it.

0:32All right, it's time to start talking

0:34about Wi-Fi communications.

0:36Now as we discovered in the last video,

0:38Wi-Fi is going to exist inside of the microwave

0:41portion of the electromagnetic spectrum.

0:44So our traditional bands of operation are going to be,

0:47for example, 2.4 gigahertz and 5 gigahertz and Wi-Fi 6,

0:51otherwise called 802.11ax is actually introducing to us

0:55the 6 gigahertz spectrum as well.

0:57Well, now that we understand frequency,

0:59we can actually start to break this down and maybe

1:01see, hey, why was a 2.4 gigahertz such a disaster?

1:05At least why don't we deploy our wireless communications

1:07into 2.4 these days?

1:09Well, one of the first things we find

1:11is that 2.4 implies that we only have 100 megahertz of frequency

1:15range in here.

1:16And so we can have a whole lot fewer channels in this space,

1:19where a channel actually represents

1:21a small range of frequencies that we

1:23would use for communications.

1:24Whereas the 5 and the 6 gigahertz,

1:26these are each roughly 1,000 megahertz.

1:29These are 10 times as large as the 2.4 gigahertz space.

1:33And so that means we get a whole lot more channels of operation.

1:36Furthermore, and this is something

1:38that will change over time, but there is a whole lot

1:40fewer devices out here that are currently

1:42using these spectrums as well.

1:44But as far as today is concerned,

1:46the 2.4 gigahertz base is so much more crowded

1:48because number one, it's just a smaller space, and number two,

1:52there are once again, a ton of different devices.

1:54And for that matter, a ton of different protocols out there

1:57and technologies that are using it.

1:59It's not just Wi-Fi, for example.

2:01I mean, it's great that we get Wi-Fi in this range,

2:03but we also have our kitchen microwaves operating

2:06in the 2.4 gigahertz spectrum.

2:08And then we also, on top of that,

2:10have other technologies such as Bluetooth.

2:12Bluetooth is not Wi-Fi, it just happens

2:14to be using the exact same wireless frequency

2:18spectrum that Wi-Fi is using.

2:19Now, this whole concept about having a crowded space,

2:22whether it's because of microwaves and Bluetooth

2:24or just because, hey, we've got other Wi-Fi devices

2:27in the range that we're trying to operate.

2:29Either way, this is where this concept of interference

2:32starts to come into play.

2:33At a surface level, I think we probably

2:35all have an understanding of what interference is.

2:37Just simply have too many talkers in the same space.

2:40I mean, imagine a sizable ballroom.

2:42And let's say you and I are sitting here

2:44having a conversation, and just for the fun of it,

2:46I'm on one end of the room, you're

2:48on the other end of the room.

2:49And so maybe we've got, I don't know, 20 feet between us.

2:52We're just sitting here having a communication.

2:55Well, our sound waves are going to be just like light waves,

2:58and that we can propagate across this free space

3:00and we can hear each other, no problem.

3:02However, now fill this ballroom with 100 other people.

3:06And let's say everybody in this ballroom

3:08is having conversations around us.

3:10How likely is it that we're still

3:12going to be able to communicate clearly with one

3:14another 20 feet away?

3:15It's probably pretty unlikely.

3:17We're probably not even going to be

3:19able to hear each other at 5 feet apart, let alone at 20.

3:22And so we're going to have to get really close to each other

3:24and start screaming at each other, which hey,

3:26screaming at one another, it's going

3:28to increase the amplitude of our waves,

3:30and so we're going to be able to hear each other even if there's

3:34interference.

3:35But here's the question.

3:36Why does this actually work?

3:38Because they're still just as many people talking around us,

3:41and so functionally speaking from a physics perspective,

3:44why does increasing my amplitude actually make it

3:47so we can hear one another?

3:48Well, this has to do with the concept of wave collisions.

3:52Because when light waves collide with one another, let's

3:54say we've got this kind of situation

3:56here where they're going to hit an impact point,

3:59they actually are going to affect one another

4:02in some fashion.

4:03In fact, if we have equal frequency

4:06and we have equal amplitude, then we're

4:09going to see some dramatic effects,

4:11because first of all, what happens

4:12if my waves are actually out of phase with one another?

4:15So out of phase, meaning that they're completely backwards.

4:18I'm doing my best here to make this

4:20about an opposite type of phase for these two

4:23different waveforms.

4:24What's going to happen here, this is basically

4:26like a math equation.

4:27I can add these two together, and I'm going

4:29to end up with a straight line.

4:31This is now my waveform down here.

4:33Well, what happened?

4:35Well, my crest got canceled out by a trough,

4:37and then my trough got canceled out by a crest here,

4:40and something in the middle got canceled out

4:42by something in the middle here, and this ends up

4:44with a big fat zero.

4:46We just completely killed both of these waveforms

4:49by colliding them with one another.

4:51Now conversely, what if I take another waveform,

4:54to be very careful here.

4:55And so I take this waveform and I combine it or I collide it,

4:58I suppose, however you want to say it,

5:00with a waveform of the same frequency,

5:02but now they're in phase with one another.

5:04Well, once again, I do my math equation, what's

5:06going to happen is I'm going to have the same frequency other

5:09than my amplitude is going to be a whole lot greater.

5:13And the reason for this is because I've

5:14added my crests together, and I've added my troughs together.

5:18Now in real life with the chaos of wireless communications,

5:21we're very rarely going to see either one of these situations

5:24exactly.

5:24Instead, we're going to have something

5:26like we grew up here, where they're

5:28intersecting at a weird angle.

5:29And as a result, some parts of the waveforms

5:32are going to get amplituded up.

5:34I imagine a better way of saying that would be amplified.

5:36I think that's what I meant to say.

5:37But either way, we're going to get amplitude it

5:40up or at some parts of the waveform

5:42are going to be canceled out, what

5:44we might call de-amplification.

5:46And so my waveform might have started

5:47like this, but by the time that it got to the other side,

5:51it actually looks sort of like this.

5:54And so these are the types of waveforms that we're really

5:56dealing with when our devices are actually receiving them.

6:00And so the question is, can I still interpret

6:02that offbeat waveform, because it doesn't look quite like it

6:06did when it was first sent.

6:08So these wave collisions actually

6:10lead us to have two different key points that we need

6:13to make sure that we have down.

6:15The first of which is that we absolutely

6:17want to make sure that we are avoiding

6:19collisions where we can.

6:20You say, well Jeff, how in the world do we avoid collisions?

6:23Well, look back up here at our ballroom example.

6:26What happens if I were to say, hey, everyone be quiet.

6:29I'm going to talk.

6:30And then I very quickly just tell you something,

6:32like hey, your shoes are untied.

6:35OK, everyone can talk again right.

6:37And so you and I have our communication first,

6:39and then somebody else has their communication second,

6:41and then somebody else goes third.

6:43And if we do this fast enough, like literally

6:45if our human brains could process like hey,

6:47I'm going to say one word at a time,

6:49and then it's your turn to say a word, well then, none of us

6:51are actually communicating at the same time.

6:53We're all effectively taking turns,

6:56and this is a big concept in the wireless world.

6:58And so we can avoid collisions that way.

7:00However, this primarily is going to affect our standards.

7:03So how we go about doing our wireless communications.

7:06In other words, how we define this in 802.11

7:09and all of its sub standards.

7:11That's going to help people who work at Cisco to develop

7:14access points that are going to affect wireless communications.

7:17This isn't really going to affect our wireless designs.

7:20However, there is a second key point

7:21that is going to affect our designs, which

7:23is that if we have two different frequencies, then

7:27there's actually no collisions here.

7:29So I would say not equal to.

7:30That's a programmer term right there.

7:32Frequency is not equal to the other frequency.

7:34Well, then that results in no interference.

7:39So what do we mean by this?

7:40Well, what we're saying here is that if I've

7:42got a waveform that looks like this,

7:44and then I've got another waveform that

7:46looks like this, well, these two waveforms

7:48can't really affect one another.

7:50I mean, there's going to be ways that they do,

7:52but in very minuscule ways and in theory,

7:55not enough that it's going to affect the outcome.

7:58And so, for example, I deploy an access point

7:59that's going to communicate like this,

8:01and maybe we call this channel 1 operation.

8:04And then we deploy a second access point,

8:06and it's operating in channel 2 in our case,

8:08let's just say, and these two frequencies don't actually

8:11align with one another well enough to cause interference.

8:14Well, guess what?

8:15We just avoided interference, even though we're

8:17talking at the exact same time.

8:19And as you can imagine, this absolutely

8:21will affect our wireless designs because we

8:23need to make sure that we're deploying

8:25the proper frequencies and the proper channels that are not

8:27going to result in interference either with one another

8:30or, by the way, with our environment.

8:33Now speaking of our environment, we

8:35do need to understand a little bit about what's

8:37happening around us as far as the wireless spectrum is

8:40concerned.

8:40And this is going to introduce a concept to us that's

8:42known as the licensed part of the spectrum

8:45and the unlicensed part of the spectrum.

8:48Now before we get into unlicensed versus licensed,

8:50one thing we might want to realize

8:52is that when we're talking about our wireless spectrum,

8:54this is sort of like real estate,

8:57because as we just established, if I'm communicating

8:59in this range right here, well, I'm

9:02the only one who should be communicating in that range.

9:05And because we only have so many frequencies,

9:07these are not H's, by the way, they're

9:08supposed to represent ranges like this.

9:10But either way, we only have so many ranges

9:13that we can distribute, and we can

9:15allow people to create devices that

9:17speak within these frequencies.

9:19And so in order to avoid interference,

9:20we have this concept of the licensed spectrum.

9:23The licensed spectrum is where a company or a vendor

9:25will actually pay money, and they get a reserved frequency.

9:29And so we think about TV stations

9:31and how they are reserved to use a particular frequency

9:34for their channel ID.

9:36We think of cell towers and such.

9:37And so if somebody has paid money in the regional area with

9:40the regional authorities to reserve a spectrum,

9:44a part of the spectrum for themselves,

9:45then we cannot use that part of the spectrum.

9:49We are operating against the regional authorities

9:52if we try to do that.

9:53And so all of our Wi-Fi devices are actually

9:55going to live inside of this unlicensed spectrum.

9:59And these frequency ranges right here

10:01are all part of that unlicensed spectrum.

10:03But what this means is that we're

10:04going to end up with devices like this over here,

10:07where we have microwaves and Bluetooth

10:09and all kinds of other wireless communications, in this space.

10:12I mean, some of my TV remotes actually

10:15use 2.4 now rather than using infrared or something

10:18like that.

10:19And so we've got all kinds of devices in our homes

10:21that are competing with the Wi-Fi.

10:23But the reason for that is because we all

10:25live in the unlicensed space.

10:27This is to say that, hey yeah, Cisco,

10:28you can make devices for Wi-Fi.

10:31But hey, so can your competitors.

10:33So can HP, for example, they can also

10:35make devices in this frequency range

10:38because Cisco didn't actually purchase this range,

10:41and that's fine because we're looking

10:42for an open environment.

10:44But this is also why we're bound to the frequency spectrums that

10:47have been opened or maybe haven't been opened to us.

10:50For example, the 6 gigahertz spectrum

10:52was never opened to us.

10:53We could never actually use it for Wi-Fi.

10:55But Wi-Fi is starting to become so crowded in the 5 gig range

10:59that the regional authorities in a lot of places in the world

11:01have established that you know what?

11:03We're going to go ahead and open the 6 gigahertz range as well.

11:06And so we're going to have a nice clean start.

11:08I imagine eventually it's going to get crowded just like the 5

11:11gigahertz range did, but at least it's

11:13more real estate for us to work with.

11:15And so this is one of the advantages to Wi-Fi 6,

11:17is just having more real estate to work with

11:19and ideally having lower interference

11:22type of environment.

11:23So as we walk away from this conversation,

11:25we should understand that Wi-Fi communications

11:27exist inside the microwave part of the electromagnetic

11:31spectrum.

11:32But also that they're existing within these specific bands.

11:36So we have the 2.4 gigahertz band, the 5 and the 6.

11:39And especially as we start to see these bands as more

11:41like real estate, we do start to understand that,

11:43oh wow, that 2.4 gigahertz range is

11:45a tenth the size of these other ranges,

11:47and that does impact things like interference.

11:50Now we look at interference, you don't

11:52have to be super technical to understand that Wi-Fi devices

11:55interfere with one another.

11:56I dare say that the non-technical world

11:58has a grasp on that.

11:59But when we look at the physics and the waveforms,

12:02and we start to see why interference occurs,

12:04it starts to make sense for us, number one, what's really

12:06happening, but also number two that, hey, interference

12:10only happens when we have the same frequencies.

12:12And that's really going to impact our designs because we

12:14want to make sure we're spreading out our frequencies

12:17as far apart as possible.

12:18If we do have to use the same frequency,

12:19let's make sure that they never actually are

12:22existing within the same space.

12:23Now lastly, we talked about licensed versus unlicensed.

12:27And this is important to start to understand

12:29as much as anything because even parts of the unlicensed space

12:32are going to be off limits to us.

12:34We have to understand certain channels within the 5 gigahertz

12:36range, we might be able to use in some circumstances,

12:39we might not be able to use in others.

12:40It also depends on where in the world you live,

12:42because what's licensed in one country

12:44or off limits in one country might be fully

12:47available in another country.

12:49And so once we start to understand

12:51once again that OK, these electromagnetic spectrum,

12:54this is like real estate now, we're

12:56assigning different parts of the spectrum out,

12:58we do start to understand what exactly is happening there.

13:01And hopefully, when we hear rules like you

13:04can use this band or you can't use that band, that we

13:07start to understand why.

13:08I hope this has been informative for you,

13:10and I'd like to thank you for viewing.

0:05Well, we have reached the end of a skill.

0:07And I always like to end a skill with a quiz

0:09to make sure that we've got everything down

0:10that we need to know.

0:11First up out of three questions--

0:13identify the crest trough origin and amplitude of this waveform.

0:17And by the way, feel free to always pause these questions

0:19and make sure that you have enough time

0:21to answer them yourself.

0:27All right, so the crest is the top part

0:29of the waveform, the topmost part.

0:31And so we have a crest here.

0:32We have a crest over here.

0:34And then trough's the exact same thing,

0:36but on the opposite side.

0:38And so we have a trough here.

0:39We have a trough here.

0:40Now, the origin that would be the middle point.

0:42And so we should be properly oscillating, actually,

0:45the exact same distance above the line and below the line--

0:49when I say the line, I suppose, the line of origin.

0:51And furthermore, when we're talking

0:53about the amplitude, this arrow that I just drew,

0:55it does represent the amplitude because we're

0:57talking about the distance from the origin,

1:00the point of origin, that the waveform actually extends.

1:03But one key part about the amplitude

1:05is that it only goes in one direction.

1:07So truly, this represents the amplitude, not

1:10the entire thing.

1:11We're not talking about the amplitude from crest

1:13to trough, but from crest to origin-- or hey,

1:15from trough to origin as well.

1:17This right here would also represent the amplitude.

1:20And on a properly formed waveform,

1:22those two numbers should actually be the exact same.

1:25And so hopefully that helps us to understand

1:27what a waveform looks like.

1:28And so as we start seeing more waveforms

1:30in our communications, we do hear something

1:32about the crest of the wave, we know what we're talking about.

1:35Question 2, as the frequency of a light wave increases,

1:38what happens as a result?

1:45So let's think back to the electromagnetic spectrum.

1:47Remember, our visible range is right here in the middle,

1:49and we have all of the infrared and below spectrums

1:52to the left, and we have all of our ultraviolet

1:55on up types of spectrums to the right.

1:57And so we know that radio waves are down here,

2:00and then we've also got cellular towers and Wi-Fi.

2:03And as our frequency is increasing,

2:05we can maybe start to think along

2:06the lines of how these different waveforms operate.

2:09And so we know it's not going to become more visible,

2:11because as frequency continues to increase,

2:14yeah, it does eventually become visible,

2:16starting from a radio wave, for example.

2:18But eventually, it's going to go invisible again.

2:20And so A is out.

2:21Now, the amplitude has nothing to do with the frequency.

2:24We can have a waveform that has a low frequency and that's

2:28got a specific amplitude, but then I

2:30can draw a waveform that has a much higher frequency,

2:33but the amplitude-- remember, from origin

2:35up-- this amplitude is just the exact same as the amplitude

2:40in this drawing down here.

2:41And so B is also out.

2:43Now, C, it becoming safer to humans, absolutely not.

2:46We know the higher the frequency up here,

2:48we start getting into X-rays and gamma rays.

2:50And if you've read enough comic books,

2:52you know that gamma rays are really bad for you.

2:54So all that to say, it definitely

2:56becomes unsafe to humans.

2:57And then the letter D here is our last choice,

3:00so hopefully it's right.

3:01The distance of propagation decreases.

3:03This is the case.

3:04We know that TV and radio waves, those

3:06can go a whole lot further and pass

3:08through objects a whole lot more seamlessly than cellular.

3:12And cellular can do so a whole lot more seamlessly than Wi-Fi.

3:15And it doesn't just stop there, because we

3:17know that going from 2.4 to 5 gigahertz

3:19within the Wi-Fi spectrum actually decreases the distance

3:23that those waveforms propagate.

3:25And so this is an important part of our wireless

3:27designs to understand that frequency is tied to distance.

3:30And so the higher the frequency we go,

3:32we can expect that our range is going to decrease.

3:36And last question, in what situation will two light waves

3:39cancel each other out?

3:45Well, the answer here would be B, when

3:46they're perfectly out of phase.

3:48Remember that concept of phase just depends on how exactly

3:52you start the waveform.

3:53And so if I've got this waveform starting here,

3:55but then I've got another waveform that

3:57starts differently, and so it's actually

3:59very clearly the opposite of the current waveform,

4:02well, at that point, we are completely out of phase

4:04with one another.

4:05And we do our math operation and add it up,

4:07and it's going to result in a big, flat line.

4:09If they're perfectly in phase with one another, so

4:11something like this, where it's the exact same thing,

4:14well, then, now our amplitude is actually

4:15going to go up in that situation.

4:18So definitely not in phase.

4:19If they're partially out of phase or partially in phase,

4:21however you want to say it, it's just

4:23going to result in just really messing up our waveform.

4:26And then if they're going in opposite directions,

4:28it doesn't actually matter.

4:30What we care about is the frequency itself,

4:33as well as how the waves align within the waveforms.

4:36So B, being perfectly out of phase,

4:38that would be our answer.

4:39Well, that wraps up this quiz.

4:41If you found that some of this knowledge and information

4:43actually canceled each other out in your mind,

4:45then be sure to go back and watch the appropriate videos

4:47in order to fill any knowledge gaps that may have occurred.

4:49Otherwise, congratulations on completing

4:51Describe Wireless Physics.

4:52I hope this has been informative for you,

4:54and I'd like to thank you for viewing.