WEBVTT

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 Hello and welcome to this video titled
 Wi-Fi modulation techniques.

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 In this video I'm going to talk about
 this term what is modulation, what

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 does it mean, and we're going to look
 at the four primary things that

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 you could modulate in a Wi-Fi signal
 frequency, wavelength, amplitude,

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 and phase. So let's start by talking about
 what is this term called modulation.

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 We know that radio frequency at its
 heart is really just electromagnetic

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 radiation. And electromagnetic radiation
 has several different descriptive

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 properties, several different
 ways we can measure it.

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 These properties or these individual
 characteristics that we can measure

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 can be artificially changed over time
 to encode data and this process

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 is called modulation.

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 Let me give you a real
 life example of this.

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 Let's forget about radio
 waves for a second.

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 Let's say that you and I are best friends
 and I know you're my best friend.

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 So we're not imagining here.

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 You're my best friend but let's take
 it back in time and we were like

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 ten years old. And we live across
 the street from each other.

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 As a matter of fact the window of my
 bedroom faces the window of your

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 bedroom. And we get into our heads that
 hey, it'd be kind of fun at night

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 to use flashlights and shine the flashlights
 to each other to encode signals.

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 Oh my dad was really
 angry tonight.

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 I didn't eat my beans.

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 Oh my mom spanked me tonight.

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 You know, whatever we want to say, we want
 to encode that with our flashlights.

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 Well, how are we actually now, if I
 just turn my flashlight on and shine

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 it in your face and I leave it on,
 can't really encode data that way.

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 I have to somehow change the flashlight
 to encode what I'm trying to tell

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 you. And the change I'm making
 is what's called modulation.

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 Now what I could do is I could
 do real simple modulation.

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 For example, I could do like
 Morse code on off, on off.

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 And depending on how long it's on or
 how long it's off, that is Morse

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 code dictates certain letters.

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 That's one way of modulation.

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 And certainly if I do that, I can get
 my information across to you at

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 a certain rate. It really depends on
 how quickly I can do my dots and

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 dashes in Morse code, you know, turn on
 for certain length, off for certain

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 length, and how quickly
 you can read it.

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 But we could go above
 and beyond that.

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 What if I could modulate two
 or more things at once?

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 What if not only could I modulate whether
 it's on, how long it's on and

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 how long it's off, what if in addition
 to that, I can modulate the color.

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 When it's on, it might be blue.

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 The next time it's on,
 it might be red.

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 Well, if I could modulate the color,
 now it can maybe encode even more

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 data. If it's on for two seconds, but
 it's red, that might be an A and

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 an E. If it's on for two seconds and
 it's blue, that might be a T and

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 an H. I can encode maybe multiple
 letters at once with that.

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 What if I modulate
 even a third thing?

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 Maybe when I have it on, it's facing
 straight at your eyeballs right now.

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 That means one thing.

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 What if I turn it on next time and
 I have it at a slight angle, where

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 it's not quite hitting your face, but
 it's hitting a little bit off to

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 the side? Depending on the angle of
 the light of my flashlight, that can

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 also encode data.

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 That's another thing I could modulate
 or change over time to mean something

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 specific. Let's take a look at what are
 the aspects of radio frequencies?

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 What are the characteristics of radio
 frequencies that I can change over

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 time to actually encode data?

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 Just like in my example there, where
 I was modulating various aspects

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 all at once, like color, direction,
 on or off, I could do that all at

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 once. These various things we're going
 to talk about here could either

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 be modulated individually or we could
 sort of combine them together to

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 get even higher data rates.

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 In no particular order, the first thing
 I'm going to talk about is the

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 modulation of frequency.

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 We know that electromagnetic radiation,
 I'm just going to call it radio

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 waves from this point, radio frequency
 has a certain oscillation.

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 Because it has an electromagnetic component,
 we can measure how strong

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 it is, and like a magnet, we can measure
 it like attractive and repulsive

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 force, and that creates a wave.

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 The greater the frequency, the more this
 wave changes over a given period

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 of time, the more data
 we can encode into it.

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 So for example, both of these waveforms
 here are measured over one second,

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 but the waveform on the left has less
 changes than the waveform on the

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 right. We would say the waveform on the
 right has a higher frequency than

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 the waveform on the left.

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 So the waveform on the right, because
 it's changing more often in that

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 one second period, I could actually
 encode that to mean more ones and

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 zeros of data than the
 waveform on the left.

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 So we actually call this frequency
 modulation, which is modifying the

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 frequency of a signal
 to encode data.

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 Think about your radio
 and your car.

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 A lot of us listen to radio stations
 that are FM radio stations.

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 So now if you think about that,
 that is frequency modulation.

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 Now, here's a big difference.

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 In the world of Wi-Fi, we're talking about
 things are modulating or changing

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 at billions of times
 in one second.

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 That would be in gigahertz.

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 The radio stations you're listening to
 in your car are still pretty fast,

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 but they're not modulating
 that fast.

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 They are megahertz stations,
 millions of times per second.

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 So 98.5, that station is oscillating
 98.5 millions of times per second.

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 The next station down
 might be 96.1.

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 That's oscillating a little bit slower,
 but your radio is able to tune

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 into those. And depending on the oscillation
 rate, it can encode the data

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 as, in this case, audio signals,
 like audio signals.

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 Advertisements or songs
 or something like that.

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 Well, with radio waves with Wi-Fi, we're
 doing the same thing, but we're

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 oscillating much, much faster.

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 So here's an example of by changing
 the frequency, I can actually encode

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 data. So within the first second, we're
 modulating in a certain frequency.

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 That might represent
 a 1 or a 1 and a 0.

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 The next second, we've increased
 the frequency.

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 Now it's oscillating a little bit faster,
 and that could mean something

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 else. So like I mentioned, radio frequency
 changes in the world of radio

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 frequency is millions or more likely
 billions of changes per second.

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 And this is why you'll notice that when
 Wi-Fi first came out, it operated

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 at the slower end of the spectrum.


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 Most Wi-Fi when it first came out
 was in the 2.4 gigahertz space.

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 So that meant roughly 2.4 billions
 of changes in one second of time.

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 Then with the newer Wi-Fi standards,
 they started moving towards the 5

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 gigahertz frequency space,
 5 billion changes per time.

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 And just like we saw right here, the
 faster your frequency, the more data

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 you can encode. Okay, so that's one thing
 you can change or modulate with

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 radio. What's another
 thing you can change?

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 Now this thing here, wavelength, I'm
 going to talk about so you understand

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 the theory of wavelength, but this isn't
 something necessarily that you

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 would artificially manipulate.

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 So wavelength is measured in meters,
 and wavelength is directly related

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 to frequency. So for example, here we
 have a wave, and the distance between

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 point A and point B, that would
 be considered our wavelength.

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 Now wavelength is inversely
 proportional to frequency.

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 What does that mean?

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 That means the more often you're changing
 something, the higher the frequency,

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 the shorter the wavelength.

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 Now here, why do we
 care about this?

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 Well, from a Wi-Fi perspective, the
 longer the wavelength, the better

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 a signal propagates
 through things.

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 So for example, here we
 have two radio waves.

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 The one on the left has a lower frequency,
 so over one second it's not

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 changing as often as
 the one on the right.

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 So we could say, well, you might say,
 well, the one on the right is better,

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 right? Because the one on the right,
 because it has a higher frequency,

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 we can encode more data on it.

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 That's true, but there's
 a trade-off.

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 Because remember, the longer the wavelength,
 the longer the space between

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 point A and point B, the more that radio
 wave will propagate through human

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 beings, through walls, even through
 the air, and maybe through raindrops

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 around us. So if we think about the
 ISM bands, how one was in the 2.4

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 gigahertz space, another was in the 5
 gigahertz space, your initial reaction

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 might be, oh, well, I've got an access
 point that has two radios, 2.4

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 and 5. I don't even want to bother using
 the 2.4 radio because I get faster

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 data rates using the
 5 gigahertz radio.

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 Well, that's true, but if we take a
 look at our environment, if between

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 that access point and your stations,
 your laptops, your clients, your

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 PCs, you have a lot of walls, a lot
 of drywall, a lot of wood furniture,

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 a lot of curtains and hangings, a lot
 of stuff, that 5 gigahertz signal

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 is not going to be able to penetrate
 through those things as well as the

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 slower 2.4 gigahertz signal, because
 the 2.4 gigahertz signal has a longer

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 wavelength, and that's one
 of the properties of RF.

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 The longer the wavelength, the better
 it can push through things.

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 So that would be a consideration
 you might want to have.

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 Another thing that we can
 modulate is the amplitude.

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 Now, amplitude is a measurement of
 the overall strength or power of a

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 radio frequency signal.

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 Amplitude can also be modulated
 to encode data.

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 So, for example, right here, we have
 a signal where at some points in

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 time, if I was measuring the actual raw,
 you know, electromagnetic energy,

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 the electromagnetic energy at this point
 in time is very strong, whereas

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 the electromagnetic energy right here
 at this other point in time is a

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 little bit weaker.

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 I could use that to encode 1s
 and 0s, to encode my data.

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 That is called amplitude
 modulation.

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 And we can certainly
 do that with RF.

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 Now, here's the thing to consider about
 amplitude, the strength, the power,

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 the amplitude of a radio frequency
 greatly weakens over distance, and

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 as it passes through objects.

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 This physical reaction of it weakening,
 we actually have a term for that,

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 we call that attenuation.

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 Look at the signal right here.

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 It starts out really strong, and then
 as it gets further and further away

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 from its source, it weakens.

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 And we call that attenuation.

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 So, in the world of radio frequencies,
 it's actually amazing how fast

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 radio frequency attenuates over
 just a little bit of distance.

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 For example, most of your Wi-Fi transmitters,
 let's take an access point

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 as an example. A Wi-Fi access point,
 when the transmitter inside the guts

0:11:26.320000 --> 0:11:30.320000
 of that access point is sending the
 electrical signal up to the antenna,

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 so that's moving electrons which is
 going to create this electromagnetic

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 radiation that emits from the antenna,
 that starts out relatively weak.

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 A strong and a strong access point might
 be transmitting at 100 milliwatts.

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 That's not from the standpoint of microwave
 ovens and light bulbs and

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 TVs. That would not be enough to power any
 of those things, but it's considered

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 a very strong signal
 in Wi-Fi terminology.

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 So, if my laptop, if my antenna is
 like one quarter of an inch or one

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 quarter of a centimeter away from the
 antenna of the access points, right

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 up next to it, I'm going to
 get most of that signal.

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 But if I'm even just a couple of feet
 away, the power, the amplitude of

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 that signal, drops dramatically.

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 As a matter of fact, I might be getting
 a tiny, if I'm 10 or 15 feet away

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 from that access point, I might be
 getting one one thousandth of that

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 signal. And yet what's awesome about
 this is that Wi-Fi antennas can pick

0:12:32.640000 --> 0:12:38.060000
 up a signal that week and still
 process the data inside of it.

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 So, the takeaway from this here is that
 attenuation happens over distance

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 and it happens very, very
 quickly over distance.

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 And that's just the air.

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 If that signal is trying to push through
 something like a wall or a human

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 body, it's going to attenuate
 even faster than that.

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 And then the last thing that we can
 modulate with regards to Wi-Fi is

0:12:59.460000 --> 0:13:01.520000
 something called phase.

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 Now, phase is really a comparison of
 two Wi-Fi signals against each other,

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 two waveforms between RF signals.

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 We know that RF signal
 has a waveform.

0:13:13.160000 --> 0:13:14.780000
 It gets strong, then it gets weak.


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 It gets strong. Or maybe if we're measuring
 frequency, you know, gets

0:13:19.780000 --> 0:13:22.520000
 real fast and really slow, real fast,
 really slow, but we can look at

0:13:22.520000 --> 0:13:25.540000
 one signal and sort of
 plot it out as a wave.

0:13:25.540000 --> 0:13:30.400000
 What if I was sending you two signals
 at once, simultaneously?

0:13:30.400000 --> 0:13:35.020000
 And during a slice of time, you sample
 the first signal and the second

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 signal and you see how do they
 line up against each other?

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 So now what you're measuring
 is what's called phase.

0:13:42.580000 --> 0:13:46.980000
 At the moment of comparison, if two waveforms
 are exactly identical, they

0:13:46.980000 --> 0:13:50.340000
 both hit their peak at exactly the same
 time or they both hit their trough

0:13:50.340000 --> 0:13:52.160000
 at exactly the same time.

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 That is considered to
 be 100% in phase.

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 So we can actually intentionally
 change this.

0:13:59.200000 --> 0:14:02.920000
 I can intentionally change, so maybe
 I'll send you one waveform which

0:14:02.920000 --> 0:14:04.080000
 is like your carrier signal.

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 This is the one that
 you lock onto.

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 This is always steady
 and consistent.

0:14:08.080000 --> 0:14:11.160000
 And then I got another one right here
 that I'm modifying the phase of

0:14:11.160000 --> 0:14:15.400000
 this waveform, and so depending on how
 it lines up to the first waveform,

0:14:15.400000 --> 0:14:17.260000
 we'll encode certain data.

0:14:17.260000 --> 0:14:18.300000
 Like look at these right here.

0:14:18.300000 --> 0:14:23.600000
 In time sample number one, the two
 waveforms are exactly in sync.

0:14:23.600000 --> 0:14:26.220000
 That might represent like a
 zero and a one or something.

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 In the very next time slot, I slightly
 modify the waveform of the red

0:14:31.080000 --> 0:14:34.200000
 signal, so now it's
 exactly opposite.

0:14:34.200000 --> 0:14:36.680000
 It's 180 degrees out of phase.

0:14:36.680000 --> 0:14:38.780000
 That would mean something else.

0:14:38.780000 --> 0:14:43.440000
 Or maybe the next time slot, I modify
 it so it's just slightly different.

0:14:43.440000 --> 0:14:45.320000
 They almost line up but not quite.


0:14:45.320000 --> 0:14:47.220000
 Well that's also not in phase.

0:14:47.220000 --> 0:14:50.340000
 That might be considered like 30 degrees
 out of phase or something like

0:14:50.340000 --> 0:14:54.240000
 that. That could also be
 used to encode data.

0:14:54.240000 --> 0:14:59.460000
 And with the newer Wi-Fi technologies,
 they incorporate all of this.

0:14:59.460000 --> 0:15:03.040000
 In order to get the really fast data rates,
 they will modulate the amplitude

0:15:03.040000 --> 0:15:07.760000
 and the frequency and the phase all
 together to give you really super

0:15:07.760000 --> 0:15:10.300000
 fast data rates.

0:15:10.300000 --> 0:15:15.140000
 So that concludes this video on modulation
 techniques, and I hope you

0:15:15.140000 --> 0:15:16.240000
 found it useful.

0:15:16.240000 --> 0:15:16.780000
 Thank you for watching.