Describe Wireless Physics

0:05Welcome to Describe Wireless Physics. And furthermore, welcome to the ENWLSD course. So we are setting off on a journey to start to explore wireless networking from a design perspective. Now, we might have a whole lot of different backgrounds here. Maybe we're trying to get the CCNP Enterprise, and we know that we need the ENCOR, the core exam, as well as a concentration exam. And so hey, this one qualifies. Maybe we can pass this exam as part of our CCNP journey. However, for other of us, we simply want to step into becoming a network architect.

0:37And part of that might mean that we need to better understand wireless design. And so maybe you have an extensive wireless background, and you've deployed and installed and managed and configured wireless networks. Or maybe you're more on the routing and switching side, and you've spent a lot of time in the IP and Ethernet world, and now you need a better understand design to just make us a better well-rounded design engineer. So whatever the background is, we're going to learn a whole lot about wireless, and again, especially focusing from a design perspective.

1:07Now, as far as this skill is concerned, you may already be scratching your head and saying, wait a second, Jeff, Describe Wireless Physics? I signed up to learn about Cisco wireless networking. Why are we having a physics lesson here? Well, because if we're going to be a well-rounded wireless engineer, and really, generally speaking, if we want to be really good at wireless networking, we need to understand how wireless communications work. And so before we dive into the blueprint of this exam, what we want to do is we want to take a look at making sure that we understand what wireless communication is from the ground up, starting with a physics lesson.

1:42So we need to understand what exactly light is, and why exactly we're talking about it, because Wi-Fi is light communications. We need to make sure that we understand what frequency and wavelength are because we're going to be talking extensively about frequency and wavelength throughout this course. Don't worry. We're going to be relating this constantly back to Wi-Fi to make sure that we're staying grounded, because, yes, it's great to learn the wave particle duality of light, right? I mean, who wouldn't want to know that. It's a great party trick to start to talk about E equals mc squared and what the constant c stands for and such.

2:16But at the same time, if we're not relating this back to why it matters and why Wi-Fi designs need to consider all of this, well, then, we're not doing ourselves any favors. So all that to say, let's go ahead and dive into this physics lesson to make sure that we understand what Wi-Fi communication even is and what this wave particle duality concept is, but how that starts to affect our wireless design, especially as we dive into things like wireless frequency and wavelengths. So with that, I will see you in the next video.

0:05This conversation around the physics of light is giving me some serious flashbacks because I studied this extensively in my university experience. I didn't actually go to get a degree in IT, just sort of ended up here. In fact, my understanding of Wi-Fi is actually what got me into IT. Because I started as a wireless installer, which quickly led to me doing wireless designs very shortly out of college. And so as we start talking about all of these different concepts of physics and light waves and everything like that, we do need to understand that there is a connection to our Wi-Fi networks.

0:37We need to be able to do site surveys, where we're looking at a room and saying, OK, I understand what the light waves are going to do here. I understand how they're going to propagate down a hallway, or how they're going to be maybe absorbed by different types of materials into my environment. And so the more I understand about light from a physics perspective, the better I'm going to be at performing some of these site surveys. So let's go ahead and dive in and start to talk a little bit about the physical nature of light. All right, so first of all, why are we even talking about light at all? Well, it might come as a surprise to some of us, but when we're talking about wireless communications like Wi-Fi, this is using light in order to communicate.

1:12And while we can't just look at a Wi-Fi device and see it blinking, that's effectively what it's doing. However, in this case, it's actually using a range of light that cannot be seen by the human eye. And so once again, I could look up at the access point, and aside from maybe a status LED, I'm not actually going to see the light that's being emitted by that device. And so when we think about wireless communication, we need to start realizing that if I'm going to transmit from this dot on the left, I suppose, and receive from the device or dot here on the right that we're going to be transmitting using light waves.

1:46And so everything that we think about, from, hey, how is this light wave going to propagate, how is the signal going to get absorbed by the environment, all of this comes back to the fact that it is actually light waves that are being transmitted. Now, if you've ever taken any physics courses in high school or college, you may have found that you needed to ask a very important question, which is, what exactly is light? And I'm going to tell you right now that this is a question that physicists have been trying to figure out in greater detail over the last several hundred years.

2:17And the conclusion, as best we can tell today, is that light is sort of like a wave. It sometimes behaves that way. But it's also sort of a particle. You think of a particle as something solid. A little ball, for example, that's being flung across the room-- you could call that a particle. And so is it a wave, or is it a particle? And the answer from a physics perspective is it's actually both. This is what we call the wave particle duality theory. And as fancy as this phrase sounds, it really is just saying that there is a dual nature to light.

2:48It's running in two different fashions. We have the wave side of it, and we have the particle side of it. So it's behaving like both of them, just depending on the situation. A lot of this understanding comes back to, believe it or not, the late 1800s and the early 1900s. This is when a lot of this discovery was taking place. We might know some of the scientists who were involved. Probably a lot of us know who Einstein is. But then we also talk about Maxwell Planck, as well as Niels Bohr. And there are a couple of very famous experiments that ended up explaining this dual nature to light.

3:21First of all, we had the double slit experiment. The double slit simply proved that light behaves like a wave. And so this is to demonstrate the wave nature of light. This experiment allows us to shine light waves through-- we'll call it a barrier-- a paper, what have you, that has two slits in it, one here and one here. And the result is that we actually see that light comes through in waves in such a way that we start to see them interfering with one another here. And this results in a pattern that looks in a specific fashion that more or less proves that this is what's happening, that light is behaving like waves.

3:56And for a long time in the physics world, because of this experiment, it was well thought of that light was simply waves. However, eventually we realized that there is another problem that we needed to solve, which is known as the photoelectric effect. The photoelectric effect says that if I'm going to shine light onto a metal plate that there's going to be some number of electrons that are emitted as a result. And the amount of electrons that are emitted actually has to do with the frequency of the light. And what was ultimately concluded is that the amount of energy that was being absorbed by the plate and converted into electrons being emitted was actually being absorbed in discrete quantities.

4:33Now, if light was purely 100% waves, then we wouldn't ever see anything discrete happening here because this is an analog signal. And so as a little bit is absorbed, we'd fire off electrons, so to speak. But this discrete nature actually tells us that light is also behaving like actual particles. And so this is an experiment that was run by Einstein. And by the way, this actually won him the Physics Nobel Prize in 1921. And so this was a very big deal in discovering that light actually can behave as both, both as waves and as particles.

5:04Now, the last thing I want to talk about as far as the physics of light is concerned would be the speed of light. Light is not actually instantaneous. It's like when we talked about up here, how we said that light is being propagated across this distance. And furthermore, the speed of light is what's known as a constant, meaning that it never changes, at least as far as when it's in a vacuum, when nothing is impeding it. This constant is known as c. And it actually shows up in that famous Einstein equation, E equals mc squared. This c right here is actually the speed of light.

5:34So it's energy is equal to mass times the speed of light squared is what this relationship is describing. And so this value of c has been extensively measured, especially now in our modern era with all of the fancy equipment that we have. And we've got it down pretty well. I'm just going to round here, but essentially, it comes down to being 2.99 times 10 to the eighth meters per second. This is very, very fast. This is why, from the human eye perspective, we can never detect that light is moving over the course of time. However, if we stretch it out across great distances, we start to see this come to life.

6:08Because if I'm going to look at the sun, for example, it actually takes eight minutes for the light to get from the sun to the Earth. And so we could often joke, if I'm looking at the sun, the sun could have exploded five minutes ago and I'm not going to know because the light showing the explosion is still only halfway to Earth. And so it's sort of a funny little concept to say, hey, we're looking back in time, what we're seeing is what was happening on the sun eight minutes ago. Now, we can stretch it out even further to say that, hey, we've got the nearest star is what's known as Alpha Centauri.

6:39And technically, it's a cluster of three stars. But either way, we've got three stars out here that are so far away that it actually takes four years for the light to get to us. And I know. I drew the arrow a little bit backwards here. The light's coming from Alpha Centauri to Earth. And so when I look up at the night sky and I see Alpha Centauri out there, that light is four years old. And the reason why it takes so long for the light to get here is because it's actually about 93 million miles away. Or for those who measure in kilometers, we're talking about 150 million kilometers.

7:11This is where we get that other measurement of distance. We talk about miles and kilometers, but we also talk about the concept of the light year. When we talk about a light year, it sounds like a measure of time because year is a measure of time. However, the light year is talking about distance. It's the distance that the light can go in a single year. And so Alpha Centauri is four light years away-- really, about 4.3, 4.35, something like that. But we'll cover astronomy in another session. Either way, we're talking about four light years away. That's a distance of measurement between Earth and the nearest star.

7:43Now, one thing to keep in mind in all of this is that this speed of light right here, yes, it's a constant, meaning it's always this fast. But at the same time, it is affected by the medium. And when I say medium, what I mean is if it goes through air, for example, or it goes through water or it goes through a material, it's going to get slowed down. This is the speed in a vacuum, meaning nothing is impeding it. And so we should keep that in mind as well. So this is wonderful and all, but let's bring this back to the idea of Wi-Fi. Why are we talking about all of this physics of light when we're really here to learn about Wi-Fi and wireless networking?

8:19Well, as far as Wi-Fi is concerned, we are primarily going to be focusing on the wave nature of light. And so everything we talked about over here, as far as the double slit experiment and the fact that it does behave like a wave, this is very important. If we don't understand this, we're going to have a hard time being wireless design engineers. The wave nature of light is going to lead to conversations around frequency and wavelength, which are extremely important concepts when it comes to doing our wireless site surveys and understanding what we're looking for when we're talking about interference and possibly materials that might absorb wireless signals.

8:52This is going to help us understand how light waves propagate because if we're going to install, for example, two wireless bridges, well, wireless bridges over the course of a great distance. And this can be affected, for example, by the curvature of the Earth. And it can be affected by the fact that Wi-Fi is not a direct line of sight concept. If I have a bridge on this side and a bridge on this side, Wi-Fi signal does not look like that. That would be wonderful if it did. But really, it's looking like this. And so we know that we've got waves, which actually creates quite a larger boundary of space where those Wi-Fi waves are going to exist.

9:27And so this has to do with Fresnel Zone concept that we're going to have to study if we want to deploy wireless bridging. So just a little teaser there for when that comes up. Now, the speed of light isn't going to really affect us that much. This is something that's fun to know. However, I will say this. As far as optical networking is concerned, keep in mind, optical networking relies on the speed of light as well. And if I were to take the distance between New York and London, that's a distance of about 3,500 miles. Well, the speed of light can only travel from New York to London so fast, right?

9:57And so at that point, we're looking at about 18 milliseconds that that light is going to take to travel from one side to the other. Now, while that's not perceptible from a human eye perspective, going through fiber optic communications, the theoretical lowest amount of latency we can ever get is 18 milliseconds one way. And so there's not going to be such a thing as communicating between New York and London at 5 milliseconds because light can't go that fast unless we come up with some crazy technology that teleports light or something along those lines, which, hey, maybe they're working on.

10:29Who knows? But either way, the more we understand about light, the better network and especially wireless design engineers we're going to be. All right, so I don't know about you, but I love having these types of conversations. Physics is just a really entertaining subject for me. But either way, just a quick synopsis. First of all, light operates both as waves and as particles. And so we've got this wave particle duality concept that we should understand. But as far as Wi-Fi is concerned, we're definitely going to focus more on the wave nature of light communications. Now, light also has a constant speed when in a vacuum.

11:02This is that lowercase c. We see this in some famous physics equations, like E equals mc squared. And the velocity is 2.99 times 10 to the eighth meters per second. I don't think Cisco's ever going to ask us that on an exam, but it creates some fun scenarios like we talked about with the optical networking concept. And so from a wireless networking perspective-- I already said it, but I'll say it again-- our focus is going to be on the wave nature. We're going to go into a little bit more specifics here around just starting to study waves and waveforms and what that means for us because eventually, we're going to start talking about Wi-Fi interference and doing our site surveys and understanding absorption and refraction.

11:40And all of these concepts come back to the fact that light is going to operate, yes, as a particle, but also as waves. I hope this has been informative for you, and I'd like to thank you for viewing.

0:05All right, so now that we understand a little bit more about how light behaves from a physics perspective, it's time to start analyzing waveforms. We are going to need to understand these concepts of waveforms, as well as the frequency and the wavelength and some of the terminology that we're going to be studying in this video in order to properly understand wireless propagation. Let's take a look. All right, so when we are drawing out waves like this, this is known as a waveform. Waveforms can be applied to pretty much anything. And we think about light waves, which is going to be the focus of this conversation, because once again, Wi-Fi communication uses light waves.

0:38However, it can also apply to things like sound waves and water waves, and for that matter, jump ropes. A lot of physics teachers will use jump ropes to demonstrate the qualities of waves. Now there are a lot of different types of waveforms. For example, we've got square waves and triangle waves. However, when we have these nice curves, we usually call this a sine wave, or maybe a sinusoidal wave. So at this point, we need to start learning the anatomy of this waveform. For example, we have the crest of the wave. That would be right here, the highest point of the wave.

1:09Now, conversely, we have the trough of the wave. And the trough is going to be down here. And yes, that is actually how you spell it in English. Don't ask me why. But hey, that is how you spell "trough". Now, if we were to draw a line right through the middle of this waveform, we can call this the origin. And every now and again, you might hear something other than origin, like the 0 amplitude or possibly the resting point. But origin is usually what we're going to call this. And so the idea here from the beginning is that we're going to rise above the origin a certain way, come back down, hit the origin again, go below the origin, come back up.

1:43And the path that I just drew here-- let me draw it a little bit thicker. This right here is a single wave on this waveform. We start at the exact same point, so for example, here on the origin. And we end over here, also on the origin. Now, I can also take a single wave from another point. For example, I could start all the way at the crest up here. And I could come down and all the way back up. And this also represents a single wave because I start from one spot, and when I get back to that same spot at the other end of the cycle, then, hey, at that point, once again, this is a single wave.

2:15Now, the amount of time that it took for me to complete a specific wave, this is known as the period. And so we measure the period in seconds. And lastly, from a terminology perspective, we also need to concern ourselves with the amplitude. Now, the amplitude is going to describe how far off of origin the waveform goes. But it's only in one direction. We don't measure amplitude, for example, from the crest down to the trough. That's not the amplitude. Instead, the amplitude is simply from the crest to origin.

2:45Or hey, we can measure it the other way. We can measure it from origin down to the trough. Now there is one other key point of terminology before we get into maybe the most important ones, which are frequency and wavelength, but we want to mention phase. The idea of phase is to indicate where, at what point, do we really start this process right here? Because given this waveform, I could start it right here at this moment in time, or hey, I could also start it right here and do the exact same waveform, but it's just off by a little bit.

3:16And so what we can end up with is a waveform that's actually exactly out of phase of the first waveform. And at that point, what we're talking about is it's basically just going to be exactly backwards relative to it. So all of my crests should line up with troughs and vice versa. And that's not the prettiest waveform. But hey, we'll take it. So for example, again, my crest winds up with the trough here and vice versa. My crest lines up with the trough. And yes, I know it's not exactly right. But we do see that this is perfectly out of phase with one another. And so we might call this 180 degrees out of phase, or maybe negative 180 degrees, however we want to describe it.

3:52And so this will come up in our conversations around interference as well. So keep that in mind. So now the big ones. First of all frequency. We talk a lot about frequency in our wireless communications. For example, we talk about the 2.4 gigahertz spectrum and the 5 gigahertz spectrum. And when we're talking about frequency, this concept of hertz, this is going to tell us how much the frequency is. So what exactly is frequency? Well, it's the number of modulations or the number of waves that we get in a specific time period.

4:25And so we take the number of waves-- it's truly a number-- and we divide it by time. And we're going to measure this using a quantity known as hertz. And yeah, that's somebody's last name. So it's not saying I'm going to hurt you-- I'm going to "Hertz" you, I suppose. But we are going to measure it in this, and we abbreviate it with a big H And a little z. The funny thing about hertz is effectively it is representative of 1 over second. So it's actually measuring a number of occurrences per second. And so seconds here, that is our frame of reference.

4:56Now, typically, we're going to represent frequency as sort of a curly f. Every now and again, you might see it represented by the Greek letter nu, which kind of looks like a v. And especially this is going to be the case in physics circles. I'm going to come over to my pink waveform here, and I'm going to measure out, let's just say, 1 second. So let's just say that this is about 1 second in time. And then I'm going to count how many waveforms happened in that time period. And so here's one waveform right here. Remember, we've got to start at the same spot and end at the same spot. So there's one waveform. Here's another waveform.

5:27So that's two. Here's another waveform. That's three. And so assuming that lines up perfectly with 1 second, we would say that this waveform has a frequency of 3 hertz, three waves per second. And so when you extrapolate this out, if we have a single wave in a second, well, that would be 1 hertz. And it sounds weird to say 1 hertz because it sounds like it's plural, but it's not. Again, it's somebody's last name. So 1 hertz would be one per second. Now, if we were to do 1,000 waves, 1,000 cycles in a single second, this would be known as a kilohertz, "kilo" meaning 1,000.

6:02And so we should be familiar with that in the networking world, kilobits per second and such. And so we are familiar with equating it to 1,000. But then we start to get into more interesting ranges. Because if I say a million cycles per second, well, now we're talking about 1 megahertz. And lastly, if I say a billion, I'll just say 1B here, 1 billion waves in a single second, well, now we're talking about gigahertz, which should start to sound a little bit more familiar, especially since we just set it up here. Our Wi-Fi communications are happening in the 2.4 and 5 and even now the 6 gigahertz bands.

6:36And therefore, we're talking about a billion of these waveforms occurring within a single second. And that is absolutely incredible, at least it is to me. I'm pretty impressed by that. Now, the other big concept, which is actually the inverse of frequency, is the concept of the wavelength. Whereas the frequency measures the amount of waves over the course of time, the wavelength is going to actually measure the actual physical distance of the wave itself. So what I mean by that is coming back to-- let's just look at this waveform right here.

7:07So I'm trying to kind of chop it off there. So we've got a single waveform. We're going to measure from here to here, and that's going to be a physical distance. Now, for most of our conversations, this physical distance is going to be pretty small. So maybe it's in the nanometer range. That would be one-billionth of a meter. And for that matter, we might even be talking about a picometer, which is a trillionth of a meter. However, our waveforms can actually be quite long as well. We might actually be talking about actual meters when it comes to our waveforms.

7:37Or we can talk about millimeters. So at least at that point, we're talking about thousandths of a meter and something we can visualize, rather than something like a micrometer or a nanometer. And so that's really, just to flesh this all out, we've got meters, millimeters, micrometers, nanometers, and picometers. Now, wavelength is represented by the Greek letter lambda. It sort of looks like this. I believe it was chosen because it actually looks sort of like a wave, doesn't it? And what we're going to find is that as frequency increases, our wavelength is going to decrease and vice versa. If frequency decreases, then our wavelength is going to increase.

8:10They are actually directly related to one another via a specific equation that's going to involve, guess what, the speed of light, that constant c that we already talked about. The reason why is because this light wave is propagating at the speed of light. And so the distance that it's covering here is relative to that speed. And that's why this constant is going to bind our two concepts together. And so the equation here is c is equal to our wavelength times our frequency. And this relationship should make sense because if I draw a waveform that looks like this, well, that has a very high frequency.

8:43We've got 5 waveforms. Let's say that's in a second. So maybe this is a full second. There's five waveforms in there. And our wavelength right here, that measurement is very small. Now conversely, if I draw a very long wavelength, and so maybe this is 1 second as well, well, now I'm not even barely at-- what is that? About 1 and 1/2 maybe of hertz? And so frequency is a lot lower, and therefore my wavelength from here to here is much greater. This is why they're inversely proportional to one another.

9:13And so it's important to start to understand that relationship as we get deeper into Wi-Fi communications. So coming out of this conversation, we should have a good comfort level around the anatomy of the waveform. We should know what the crest is and the trough and the period and the amplitude. And we should be able to identify what these are given a specific waveform. Now, beyond those concepts, we have these two big ones, the first of which is frequency. Frequency is measuring how many waves are on this waveform per second. And we measure that in hertz. Hertz literally is just a per second type of measurement.

9:44And so if we have 1,000 waves all crammed into this waveform in a single second, well, that's going to be 1 kilohertz. Now, inverse to the frequency is the wavelength. And so the more waves that we cram into 1 second, the shorter those waves are going to have to be. And that would be the wavelength measurement. And so we just need to understand this inverse relationship. We don't necessarily have to have memorized, especially for this exam, that the speed of light is equal to wavelength times frequency. It's more just understanding that as frequency goes up, wavelength size has to go down and vice versa because that c on the other side of the equation is a constant.

10:17It never changes. And so if we do increase frequency, we will expect to see wavelength go down and vice versa. I hope this has been informative for you, and I'd like to thank you for viewing.

0:00[MUSIC PLAYING] I don't know about you, but for me, I just absolutely love a splendid sunset. Seeing all the different colors of the rainbow right there at the horizon stretching up from this bright red at the horizon to sometimes even see the oranges and the greens and then the blue of the atmosphere. And so as beautiful as that is, we can actually start to break that down into physics level conversations about what's happening, because every different color that we see is a different frequency of light.

0:32And there's an entire spectrum of light out there that the human eye can't even see. And so what we're going to do in this video is we're going to talk about this electromagnetic spectrum, we're going to understand the visible range of light that we see, but then also all of the light that we can't see, which is very important because our wireless communications, as we've already mentioned, is using light we cannot see. Let's dive in. For most of us humans, we're going to see a pretty wide range of colors. And so we see, for example, red and orange and yellow. And if you grew up English speaking, you probably learned about this concept of ROYGBIV, although I think they've gotten rid of the I now and it's just blue and violet, and we kind of got rid of indigo because we never really knew what indigo was anyways.

1:14But either way, we've got this a range of colors that is described as a spectrum. The reason why we call it a spectrum is because it's analog. We don't really know where red ends and orange begins. We just sort of see the colors blend together as we look into the sky, again looking at a rainbow or possibly looking at the sunset or maybe a reflection in the water or whatever it is that we're seeing. Now the reason we have this beautiful spectrum is because our eyes are actually equating each different frequency of light with a specific color.

1:45And so when we look at the spectrum, really what it's arranged by is it's arranged by frequency. And so we have an increasing level of frequency on the spectrum. So red would actually be the lowest frequency within the visible spectrum of light. And then violet is going to be the highest frequency that we can see. And naturally, we can see everything in between. So orange and yellow and green and blue, these all show up, even though they're in the middle of the range, so to speak. Well, this is well and good, other than that this spectrum, the visible spectrum is just a tiny sliver of the overall spectrum of light that exists.

2:19And what we find is that we've got a whole lot of light at lower frequencies we can't see, and then we've got light at higher frequencies we can't see. And we call this the electromagnetic spectrum. Now just like with the visible spectrum how red blends into orange, this electromagnetic spectrum, this is also an analog concept. And so we've got every single range of frequency possible all the way from very low to very, very high. But in order to simplify our lives a little bit, we just grouped a lot of these frequencies together into what we call different regions. Now the regions right around the visible spectrum are actually appropriately named, because this first region to the left, this is called infrared.

2:56And we look at the root word infra, it means below. So we're truly talking about light frequency that is just below red. Now on the other side, we have this light range that we call ultraviolet, because the root word ultra actually implies above or beyond. And so we've gone beyond violet, we're talking about ultraviolet light. And so here we sometimes call this UV light, it's the light that we often talk about as far as the sun is concerned. And sometimes we just need to make sure that we're protecting our skin with sunscreen because we don't want too much UV or ultraviolet light.

3:27Now the other regions down here on the left, these are called radiowaves and microwaves. And then the regions on the right, we have X-rays and we have gamma rays. So what are these different frequencies look like? Well, radiowaves are going to be really in the realm of kilohertz for the most part. If we hear that we're talking about kilohertz, that probably is going to be the radiowaves that we use, for example, to send radio and TV broadcasts in the air. Then we enter into the microwave realm, which yes, this is where our kitchen microwaves operate. But more than that, it's where our networking devices operate and our cell towers operate.

4:01We're usually talking more in the megahertz to gigahertz range when it comes to our microwave communications. And then once we start getting into the terahertz range, this is when we're talking about infrared. Now by the time we get to ultraviolet, we can no longer really use mega, giga, terra because we've really gone beyond some of those words. And so ultraviolet, for example, we're talking about maybe a 10 to the 15 kind of concept here as far as Hertz is concerned. We're talking about X-rays, you might hear something like 10 to the 18th and 10 to the 21st for gamma rays.

4:32But keep in mind that we also have to cover the full range. And so 10 to the 19th power also exists within this discrete X-ray region. And so these are estimations that we can use. However, we're not really trying to lock this down to memorize where microwaves and an infrared begins and that kind of thing. Instead, mostly what we care about are down here. Hearing kilohertz, megahertz, and gigahertz should clue us in to what type of communications we're talking about. Now something we find, especially as we analyze this range of the electromagnetic spectrum, which is really where we use light for communications, what we start to see is that the higher the frequency that we have, it's going to end up meaning that our distance that's traveled with the same amount of energy goes down.

5:18This happens for a few reasons. First of all, light is going to lose energy across what we'd call free space propagation. Well, probably more importantly as frequency increases, our ability to pass through materials is going to go down. For example, a brick wall is going to absorb higher frequencies a whole lot easier than it's going to be able to absorb lower frequencies. For example, when we think about TV and radio broadcasts, what do we think about? We think about a TV station that's probably miles away from us.

5:50We don't need to be within a half mile of the TV station in order to get that signal. We also expect it to pass through walls, because my TV antenna, I mean, yes, I can stick it up into the sky and that will get me a better reception. However, a lot of times, it's going to pass through my walls and get right to my TV. And so we compare this type of wireless communication with a different type of wireless communication, such as, well, let's just talk about cellular. Cellular is best when I'm maybe within, well, let's just say one mile of a cellular tower. And a lot of times, I know if I step inside my house, for example, my signal is actually going to go down, because the cellular signal is absorbed a whole lot more by my walls and my insulation.

6:31And so forget it, if I go into the basement, then I'm not going to get any amount of cellular signal because those waveforms are getting absorbed before they ever get to my cell phone. And lastly, we look at Wi-Fi. Wi-Fi is a higher frequency than cellular. And so when we're talking about Wi-Fi, I mean, I'd love to be able to get a Wi-Fi signal one mile away. But oftentimes, I can't even get across my house with a Wi-Fi signal. And that's just because we're using a much higher frequency. So sometimes my walls inside my house actually will absorb the Wi-Fi signal, even though I only have one wall between me and the access point.

7:07And furthermore, by the way, we are going to find, especially in our wireless designs that 2.4 gigahertz actually performs a whole lot better than five gigahertz. So I'm not by any stretch saying that we should be designing inside the 2.4 gigahertz spectrum because we should not these days. But one of the ramifications of that is my access points aren't going to go nearly as far in this five gigahertz spectrum. And so especially if I'm deploying two different frequencies and I'm supposed to be designing around these two different frequencies for some reason, that's going to make my wireless designs really tricky because an access point here will have a range that it can reach for the five gigahertz spectrum, but I'll have a much larger range that can reach for the 2.4.

7:47And so I either need to turn down the power of the 2.4 gigahertz radio in order to match the five gigahertz range, or I need to otherwise be very, very careful in my wireless designs, even though again, this example I don't expect to encounter this very often, but it is an interesting side effect to this whole frequency and distance conversation. Now, one last thing to consider as far as light frequency is concerned would be the safety to people running this type of technology. What we find as we look at light and frequency is as light increases in frequency, it actually starts to become very dangerous to the human body.

8:21The reason for this is because our light waves, our wavelengths are so small is why we're talking about maybe picometers or smaller, they can actually break into human cells. And once they break into human cells, they start to break down our chromosomes and start to result in mutations, and this results in some very bad situations. This is why the medical world is very careful around x-rays, even though it's very beneficial to us from a medical perspective to get an x, they have to track how many X-rays that we've exposed ourselves to recently because the more X-rays that 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, they have to push it right up against me because it's got to be really, really close for the distance. But this is also-- this machine right here, I suppose, the X-ray machine. But there's also why the person who's administrating the X-ray, they run behind a lead wall to make sure that they're not exposing themselves to X-rays as part of their day-to-day job. So the reason I bring this up is because the lower frequencies are considered to be very safe. So when we're talking about lower frequencies, we're talking about this entire spectrum down here.

9:29In theory, all of this frequency is a whole lot safer even than the visible spectrum, which is sitting right in the middle. So if ROYGBIV type of lighting isn't causing us any kind of health issues, then none of the frequencies down here should be causing us health issues either. Now there have been a lot of studies out there that have, some of them are leave us skeptical maybe about the health implications of some of this. It also certainly matters how close we are to access points and even our cell phones and such. But all that to say, one of the reasons why we are deploying our cellular and Wi-Fi communications into this range is in order to keep us all safe.

10:07So hopefully, that places our minds a little bit at ease, but also maybe we need to place other people's mind at ease. As a wireless design expert, we can point to the electromagnetic spectrum to assure everyone around us why we consider this technology to be safe. So as we break down this conversation of light and physics, we do find that when we're looking at different colors, that represents different frequencies to our eyes. And so when we look at the visible range of light, we see it range from red at low frequencies to violet at high frequencies.

10:38Now that's just a very small part of the overall electromagnetic spectrum. The electromagnetic spectrum goes way lower frequencies than we can see and way higher frequencies that we can see. This is why we can't see our Wi-Fi devices talking to each other, because they're communicating at a range that is too low of a frequency for us to see. And so the higher the frequency we also find, the shorter distances that we can go with the same amount of energy. And so this is why TV and radio broadcasts can go so far, and cellular towers can go not quite as far, but still pretty far, and our wireless device might be on the other side of that wall, and I'm not getting a good signal.

11:14And so understanding light frequency and understanding how that affects our distances and our propagation, as you can imagine, this is going to matter a whole lot when we start doing our wireless site surveys. I hope this has been informative for you, and I'd like to thank you for viewing.

0:00[MUSIC PLAYING] All right, we said at the start of this that if we're just going to have a physics lesson, then that's kind of fun, I suppose, but it's not going to make me a better Wi-Fi engineer. Now it's time to take all of the lessons that we've been learning and actually apply it to wireless communications. So in this video, we're going to start to introduce these concepts of interference, for example, as well as the different frequencies that we might deploy in a wireless network and start to talk about these bands and the unlicensed and the licensed spectrum.

0:30So let's just go ahead and dive in and cover it. All right, it's time to start talking about Wi-Fi communications. Now as we discovered in the last video, Wi-Fi is going to exist inside of the microwave portion of the electromagnetic spectrum. So our traditional bands of operation are going to be, for example, 2.4 gigahertz and 5 gigahertz and Wi-Fi 6, otherwise called 802.11ax is actually introducing to us the 6 gigahertz spectrum as well. Well, now that we understand frequency, we can actually start to break this down and maybe see, hey, why was a 2.4 gigahertz such a disaster?

1:05At least why don't we deploy our wireless communications into 2.4 these days? Well, one of the first things we find is that 2.4 implies that we only have 100 megahertz of frequency range in here. And so we can have a whole lot fewer channels in this space, where a channel actually represents a small range of frequencies that we would use for communications. Whereas the 5 and the 6 gigahertz, these are each roughly 1,000 megahertz. These are 10 times as large as the 2.4 gigahertz space. And so that means we get a whole lot more channels of operation.

1:36Furthermore, and this is something that will change over time, but there is a whole lot fewer devices out here that are currently using these spectrums as well. But as far as today is concerned, the 2.4 gigahertz base is so much more crowded because number one, it's just a smaller space, and number two, there are once again, a ton of different devices. And for that matter, a ton of different protocols out there and technologies that are using it. It's not just Wi-Fi, for example. I mean, it's great that we get Wi-Fi in this range, but we also have our kitchen microwaves operating in the 2.4 gigahertz spectrum.

2:08And then we also, on top of that, have other technologies such as Bluetooth. Bluetooth is not Wi-Fi, it just happens to be using the exact same wireless frequency spectrum that Wi-Fi is using. Now, this whole concept about having a crowded space, whether it's because of microwaves and Bluetooth or just because, hey, we've got other Wi-Fi devices in the range that we're trying to operate. Either way, this is where this concept of interference starts to come into play. At a surface level, I think we probably all have an understanding of what interference is. Just simply have too many talkers in the same space.

2:40I mean, imagine a sizable ballroom. And let's say you and I are sitting here having a conversation, and just for the fun of it, I'm on one end of the room, you're on the other end of the room. And so maybe we've got, I don't know, 20 feet between us. We're just sitting here having a communication. Well, our sound waves are going to be just like light waves, and that we can propagate across this free space and we can hear each other, no problem. However, now fill this ballroom with 100 other people. And let's say everybody in this ballroom is having conversations around us.

3:10How likely is it that we're still going to be able to communicate clearly with one another 20 feet away? It's probably pretty unlikely. We're probably not even going to be able to hear each other at 5 feet apart, let alone at 20. And so we're going to have to get really close to each other and start screaming at each other, which hey, screaming at one another, it's going to increase the amplitude of our waves, and so we're going to be able to hear each other even if there's interference. But here's the question. Why does this actually work? Because they're still just as many people talking around us, and so functionally speaking from a physics perspective, why does increasing my amplitude actually make it so we can hear one another?

3:48Well, this has to do with the concept of wave collisions. Because when light waves collide with one another, let's say we've got this kind of situation here where they're going to hit an impact point, they actually are going to affect one another in some fashion. In fact, if we have equal frequency and we have equal amplitude, then we're going to see some dramatic effects, because first of all, what happens if my waves are actually out of phase with one another? So out of phase, meaning that they're completely backwards. I'm doing my best here to make this about an opposite type of phase for these two different waveforms.

4:24What's going to happen here, this is basically like a math equation. I can add these two together, and I'm going to end up with a straight line. This is now my waveform down here. Well, what happened? Well, my crest got canceled out by a trough, and then my trough got canceled out by a crest here, and something in the middle got canceled out by something in the middle here, and this ends up with a big fat zero. We just completely killed both of these waveforms by colliding them with one another. Now conversely, what if I take another waveform, to be very careful here.

4:55And so I take this waveform and I combine it or I collide it, I suppose, however you want to say it, with a waveform of the same frequency, but now they're in phase with one another. Well, once again, I do my math equation, what's going to happen is I'm going to have the same frequency other than my amplitude is going to be a whole lot greater. And the reason for this is because I've added my crests together, and I've added my troughs together. Now in real life with the chaos of wireless communications, we're very rarely going to see either one of these situations exactly. Instead, we're going to have something like we grew up here, where they're intersecting at a weird angle.

5:29And as a result, some parts of the waveforms are going to get amplituded up. I imagine a better way of saying that would be amplified. I think that's what I meant to say. But either way, we're going to get amplitude it up or at some parts of the waveform are going to be canceled out, what we might call de-amplification. And so my waveform might have started like this, but by the time that it got to the other side, it actually looks sort of like this. And so these are the types of waveforms that we're really dealing with when our devices are actually receiving them.

6:00And so the question is, can I still interpret that offbeat waveform, because it doesn't look quite like it did when it was first sent. So these wave collisions actually lead us to have two different key points that we need to make sure that we have down. The first of which is that we absolutely want to make sure that we are avoiding collisions where we can. You say, well Jeff, how in the world do we avoid collisions? Well, look back up here at our ballroom example. What happens if I were to say, hey, everyone be quiet. I'm going to talk. And then I very quickly just tell you something, like hey, your shoes are untied.

6:35OK, everyone can talk again right. And so you and I have our communication first, and then somebody else has their communication second, and then somebody else goes third. And if we do this fast enough, like literally if our human brains could process like hey, I'm going to say one word at a time, and then it's your turn to say a word, well then, none of us are actually communicating at the same time. We're all effectively taking turns, and this is a big concept in the wireless world. And so we can avoid collisions that way. However, this primarily is going to affect our standards. So how we go about doing our wireless communications.

7:06In other words, how we define this in 802.11 and all of its sub standards. That's going to help people who work at Cisco to develop access points that are going to affect wireless communications. This isn't really going to affect our wireless designs. However, there is a second key point that is going to affect our designs, which is that if we have two different frequencies, then there's actually no collisions here. So I would say not equal to. That's a programmer term right there. Frequency is not equal to the other frequency. Well, then that results in no interference.

7:39So what do we mean by this? Well, what we're saying here is that if I've got a waveform that looks like this, and then I've got another waveform that looks like this, well, these two waveforms can't really affect one another. I mean, there's going to be ways that they do, but in very minuscule ways and in theory, not enough that it's going to affect the outcome. And so, for example, I deploy an access point that's going to communicate like this, and maybe we call this channel 1 operation. And then we deploy a second access point, and it's operating in channel 2 in our case, let's just say, and these two frequencies don't actually align with one another well enough to cause interference.

8:14Well, guess what? We just avoided interference, even though we're talking at the exact same time. And as you can imagine, this absolutely will affect our wireless designs because we need to make sure that we're deploying the proper frequencies and the proper channels that are not going to result in interference either with one another or, by the way, with our environment. Now speaking of our environment, we do need to understand a little bit about what's happening around us as far as the wireless spectrum is concerned. And this is going to introduce a concept to us that's known as the licensed part of the spectrum and the unlicensed part of the spectrum.

8:48Now before we get into unlicensed versus licensed, one thing we might want to realize is that when we're talking about our wireless spectrum, this is sort of like real estate, because as we just established, if I'm communicating in this range right here, well, I'm the only one who should be communicating in that range. And because we only have so many frequencies, these are not H's, by the way, they're supposed to represent ranges like this. But either way, we only have so many ranges that we can distribute, and we can allow people to create devices that speak within these frequencies.

9:19And so in order to avoid interference, we have this concept of the licensed spectrum. The licensed spectrum is where a company or a vendor will actually pay money, and they get a reserved frequency. And so we think about TV stations and how they are reserved to use a particular frequency for their channel ID. We think of cell towers and such. And so if somebody has paid money in the regional area with the regional authorities to reserve a spectrum, a part of the spectrum for themselves, then we cannot use that part of the spectrum. We are operating against the regional authorities if we try to do that.

9:53And so all of our Wi-Fi devices are actually going to live inside of this unlicensed spectrum. And these frequency ranges right here are all part of that unlicensed spectrum. But what this means is that we're going to end up with devices like this over here, where we have microwaves and Bluetooth and all kinds of other wireless communications, in this space. I mean, some of my TV remotes actually use 2.4 now rather than using infrared or something like that. And so we've got all kinds of devices in our homes that are competing with the Wi-Fi.

10:23But the reason for that is because we all live in the unlicensed space. This is to say that, hey yeah, Cisco, you can make devices for Wi-Fi. But hey, so can your competitors. So can HP, for example, they can also make devices in this frequency range because Cisco didn't actually purchase this range, and that's fine because we're looking for an open environment. But this is also why we're bound to the frequency spectrums that have been opened or maybe haven't been opened to us. For example, the 6 gigahertz spectrum was never opened to us.

10:53We could never actually use it for Wi-Fi. But Wi-Fi is starting to become so crowded in the 5 gig range that the regional authorities in a lot of places in the world have established that you know what? We're going to go ahead and open the 6 gigahertz range as well. And so we're going to have a nice clean start. I imagine eventually it's going to get crowded just like the 5 gigahertz range did, but at least it's more real estate for us to work with. And so this is one of the advantages to Wi-Fi 6, is just having more real estate to work with and ideally having lower interference type of environment.

11:23So as we walk away from this conversation, we should understand that Wi-Fi communications exist inside the microwave part of the electromagnetic spectrum. But also that they're existing within these specific bands. So we have the 2.4 gigahertz band, the 5 and the 6. And especially as we start to see these bands as more like real estate, we do start to understand that, oh wow, that 2.4 gigahertz range is a tenth the size of these other ranges, and that does impact things like interference. Now we look at interference, you don't have to be super technical to understand that Wi-Fi devices interfere with one another.

11:56I dare say that the non-technical world has a grasp on that. But when we look at the physics and the waveforms, and we start to see why interference occurs, it starts to make sense for us, number one, what's really happening, but also number two that, hey, interference only happens when we have the same frequencies. And that's really going to impact our designs because we want to make sure we're spreading out our frequencies as far apart as possible. If we do have to use the same frequency, let's make sure that they never actually are existing within the same space. Now lastly, we talked about licensed versus unlicensed.

12:27And this is important to start to understand as much as anything because even parts of the unlicensed space are going to be off limits to us. We have to understand certain channels within the 5 gigahertz range, we might be able to use in some circumstances, we might not be able to use in others. It also depends on where in the world you live, because what's licensed in one country or off limits in one country might be fully available in another country. And so once we start to understand once again that OK, these electromagnetic spectrum, this is like real estate now, we're assigning different parts of the spectrum out, we do start to understand what exactly is happening there.

13:01And hopefully, when we hear rules like you can use this band or you can't use that band, that we start to understand why. I hope this has been informative for you, and I'd like to thank you for viewing.

0:05Well, we have reached the end of a skill. And I always like to end a skill with a quiz to make sure that we've got everything down that we need to know. First up out of three questions-- identify the crest trough origin and amplitude of this waveform. And by the way, feel free to always pause these questions and make sure that you have enough time to answer them yourself. All right, so the crest is the top part of the waveform, the topmost part. And so we have a crest here. We have a crest over here. And then trough's the exact same thing, but on the opposite side.

0:38And so we have a trough here. We have a trough here. Now, the origin that would be the middle point. And so we should be properly oscillating, actually, the exact same distance above the line and below the line-- when I say the line, I suppose, the line of origin. And furthermore, when we're talking about the amplitude, this arrow that I just drew, it does represent the amplitude because we're talking about the distance from the origin, the point of origin, that the waveform actually extends. But one key part about the amplitude is that it only goes in one direction. So truly, this represents the amplitude, not the entire thing.

1:11We're not talking about the amplitude from crest to trough, but from crest to origin-- or hey, from trough to origin as well. This right here would also represent the amplitude. And on a properly formed waveform, those two numbers should actually be the exact same. And so hopefully that helps us to understand what a waveform looks like. And so as we start seeing more waveforms in our communications, we do hear something about the crest of the wave, we know what we're talking about. Question 2, as the frequency of a light wave increases, what happens as a result?

1:45So let's think back to the electromagnetic spectrum. Remember, our visible range is right here in the middle, and we have all of the infrared and below spectrums to the left, and we have all of our ultraviolet on up types of spectrums to the right. And so we know that radio waves are down here, and then we've also got cellular towers and Wi-Fi. And as our frequency is increasing, we can maybe start to think along the lines of how these different waveforms operate. And so we know it's not going to become more visible, because as frequency continues to increase, yeah, it does eventually become visible, starting from a radio wave, for example.

2:18But eventually, it's going to go invisible again. And so A is out. Now, the amplitude has nothing to do with the frequency. We can have a waveform that has a low frequency and that's got a specific amplitude, but then I can draw a waveform that has a much higher frequency, but the amplitude-- remember, from origin up-- this amplitude is just the exact same as the amplitude in this drawing down here. And so B is also out. Now, C, it becoming safer to humans, absolutely not. We know the higher the frequency up here, we start getting into X-rays and gamma rays.

2:50And if you've read enough comic books, you know that gamma rays are really bad for you. So all that to say, it definitely becomes unsafe to humans. And then the letter D here is our last choice, so hopefully it's right. The distance of propagation decreases. This is the case. We know that TV and radio waves, those can go a whole lot further and pass through objects a whole lot more seamlessly than cellular. And cellular can do so a whole lot more seamlessly than Wi-Fi. And it doesn't just stop there, because we know that going from 2.4 to 5 gigahertz within the Wi-Fi spectrum actually decreases the distance that those waveforms propagate.

3:25And so this is an important part of our wireless designs to understand that frequency is tied to distance. And so the higher the frequency we go, we can expect that our range is going to decrease. And last question, in what situation will two light waves cancel each other out? Well, the answer here would be B, when they're perfectly out of phase. Remember that concept of phase just depends on how exactly you start the waveform. And so if I've got this waveform starting here, but then I've got another waveform that starts differently, and so it's actually very clearly the opposite of the current waveform, well, at that point, we are completely out of phase with one another.

4:05And we do our math operation and add it up, and it's going to result in a big, flat line. If they're perfectly in phase with one another, so something like this, where it's the exact same thing, well, then, now our amplitude is actually going to go up in that situation. So definitely not in phase. If they're partially out of phase or partially in phase, however you want to say it, it's just going to result in just really messing up our waveform. And then if they're going in opposite directions, it doesn't actually matter. What we care about is the frequency itself, as well as how the waves align within the waveforms.

4:36So B, being perfectly out of phase, that would be our answer. Well, that wraps up this quiz. If you found that some of this knowledge and information actually canceled each other out in your mind, then be sure to go back and watch the appropriate videos in order to fill any knowledge gaps that may have occurred. Otherwise, congratulations on completing Describe Wireless Physics. I hope this has been informative for you, and I'd like to thank you for viewing.