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I'm not going to lie, I am a little bit of a physics geek. Whenever we talk

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about wireless

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communications, I love drilling into the details of our wireless waveforms and

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how we

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encode the data. It's pretty fascinating technology. Now within the scope of

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this conversation

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and this exam, we're going to be looking at things from the perspective of

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being a wireless

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network engineer, which is usually going to focus a little bit more on wireless

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design

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and making sure we understand how a lot of our wireless communications happen,
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and making sure we understand how a lot of our wireless communications happen,

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wireless topologies infrastructure, those kinds of things. But at the heart of

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wireless communications,

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we do need to understand that we are leveraging this concept of radio frequency

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, which is abbreviated

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as RF. And the question I love to ask is what exactly is radio frequency? If I

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've got an access

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point here and I've got a mobile device and they're communicating back and

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forth, I mean, what

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exactly are these waves that they're sending wirelessly? The reality is that
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exactly are these waves that they're sending wirelessly? The reality is that

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this word radio is

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kind of unfortunate. We use the word radio to describe something I'm listening

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to. And so as

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such, we typically are inclined to think that maybe radio frequency is a sound

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thing and nothing

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could be further from the truth. Radio has nothing to do with sound. In fact,

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it has to do with maybe

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what we might consider to be the opposite of sound, which is that radio
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what we might consider to be the opposite of sound, which is that radio

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frequency is actually a form

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of light. Yes, it's a form of light. When we say that we're communicating to

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one another,

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these two devices are essentially blinking light at one another. Now

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interestingly, this light

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is light that we cannot see. So it's unseen light. It exists outside the range

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of frequencies that

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our eyes can detect. And furthermore, because it is a different set of

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frequencies, it's actually

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much lower than the light that we see. They can also pass through walls and
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much lower than the light that we see. They can also pass through walls and

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obstacles and all

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kinds of things. So it doesn't behave like we might expect light to behave in

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some ways. And yet,

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light reflects off of mirrors and radio frequency reflects off of mirrors,

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reflective surfaces,

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these kinds of things. So it shares some properties. It doesn't share other

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properties. And yet,

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we compare divisible light and yet underlying all of this, it really is just a
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we compare divisible light and yet underlying all of this, it really is just a

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form of light.

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And so what we do to describe a waveform is we draw it out like this. This is

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what a wireless

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waveform looks like. And if you've ever taken a physics class, maybe you had

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one person stand on one

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end of a jump rope and the other person stand on the other end and you swing

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this up and down and

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forms these wave forms in the middle. Wave forms exist not just for light rays

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or light waves,
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or light waves,

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but also it exists in the form of sound waves and jump ropes and all kinds of

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things. So we're going

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to see these types of wave forms in a lot of places. This specifically is known

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as a sinusoidal

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waveform. And that's distinguished from things that we might see elsewhere like

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a square wave.

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We've got all kinds of other waveforms that might exist, but light is very

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analog in nature and it

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is sinusoidal as a result. Now there's a lot of parts of the waveform that we
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is sinusoidal as a result. Now there's a lot of parts of the waveform that we

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probably don't need to

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know necessarily as part of this course, but it's helpful to know. For example,

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we see peaks and

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valleys. These peaks and valleys have words that we used to describe them. For

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example, we have

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the crest and the trough at the top and bottom. We also have the waveform

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oscillating around a

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middle point that we refer to as the origin. And we might also, and this part

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is important,

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is fine that there's a level of energy at every point along the waveform. And
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is fine that there's a level of energy at every point along the waveform. And

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this level of energy

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is described as the amplitude when it's at its peak. So this much energy right

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here, or for that

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matter, this much energy down here is considered to be the amplitude. The more

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energy a waveform has,

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the greater its amplitude. We might see smaller waveforms like this that have

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much lower energy or

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waveforms that do this that have a much higher energy level. So while that's
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waveforms that do this that have a much higher energy level. So while that's

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interesting, the crest,

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the trough, the origin, they don't really help us out a lot with wireless

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communications, at least

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within the scope of this conversation. But instead, what we need to focus on a

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lot is going to be

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a couple of other elements, namely the frequency, which is right there in the

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word radio frequency,

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and our wavelength. Now, frequency is defined as the number of oscillations or

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modulations in a given

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time period. So we're talking about essentially the number of waves per second.
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time period. So we're talking about essentially the number of waves per second.

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As this waveform

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travels, we can actually measure the amount of time it takes for us to repeat

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ourselves,

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because these waveforms are going to continue to repeat over and over again.

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And so it's really just

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a matter of finding a snippet right here in the middle where we say, okay, how

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long did this take for

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us to oscillate? If we are measuring it in time, we have a word for this. This
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us to oscillate? If we are measuring it in time, we have a word for this. This

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is the period. How long

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it takes for one waveform to complete? But then we have this concept of

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frequency that now is saying,

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okay, but how many of these exist within a one second time period? And in this

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case, we see that

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we have three different waveforms inside of one second. So we have a fun unit

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of measurement for

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the frequency. It is known as the hertz, which is actually named after somebody
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the frequency. It is known as the hertz, which is actually named after somebody

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. And so anytime we

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have a unit of measurement, we name it after someone, we typically capitalize

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it. So we abbreviate

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this as a capital H lowercase z. It does sound like we're talking about

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something plural, but it's not

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plural. It's just somebody's name ends with a z. So if I have one waveform in a

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second, I would

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indeed say that it's one hertz, not like one hertz or something like that. In

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our case here, we say

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we have three waveforms in one second. And so this means that we have a
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we have three waveforms in one second. And so this means that we have a

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frequency of three hertz.

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Now, this is a very low frequency. If I want to talk about wireless

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communications, we're usually

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talking about potentially killer hertz or more often times megahertz and even

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gigahertz.

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So killer hertz, this would be a thousand. If I said it's one killer hertz, it

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's a thousand hertz.

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A megahertz, this is one million. And yes, a gigahertz is one billion. And this
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A megahertz, this is one million. And yes, a gigahertz is one billion. And this

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is typically the

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range that our Wi-Fi communications are going to communicate in. So if we are

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communicating at five

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gigahertz, we're truly squeezing five billion waveforms into a single second,

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which is pretty

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incredible. Now, here's the crazy thing. If we want to talk about Wi-Fi, we're

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talking about gigahertz.

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If we want to talk about visible light, meaning the light that we can see red

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and blue and green and
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and blue and green and

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all the beautiful colors that exist out there, then we are actually talking

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about the

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terror hertz range. And not just the terror hertz, but usually hundreds of

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terror hertz. So for

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example, we might be talking about 400 terror hertz for seeing visible light

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that's actually at

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the lower end of the spectrum that we can see. And that is talking about 400,

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000 gigahertz.

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So that is the difference between visible light and Wi-Fi and why Wi-Fi is so
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So that is the difference between visible light and Wi-Fi and why Wi-Fi is so

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much lower frequency

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than even what we see from a visible light perspective. Now, if we want to talk

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about going to the

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doctor and getting X-rays, that's even higher frequencies than visible light.

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And we have to be

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careful with the higher frequencies because that's where we can see radiation

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causing us damage

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as human beings. But anything lower than visible light is considered safe,

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which is why we use the

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lower light ranges for our wireless communications. Now, if we flip frequency
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lower light ranges for our wireless communications. Now, if we flip frequency

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around, we're going to

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find that we have another unit of measurement, which is the wavelength. The

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wavelength of a wave

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form is truly the length that's right there in the name. We can measure this in

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feet or inches or

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more likely in meters and millimeters and nanometers. So the amount of distance

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up here of one of our

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cycles, this length, or again, the distance is what the wavelength is. And so
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cycles, this length, or again, the distance is what the wavelength is. And so

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we're typically again

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talking about this in terms of nanometers, especially as it relates to anything

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in the Wi-Fi space.

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But if we're talking about much lower frequencies, then we get much longer

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wavelengths. This is

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an inversely proportional relationship inversely proportional, meaning that if

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we increase the

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frequency, the wavelength goes down because I've got more of these in here. And
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frequency, the wavelength goes down because I've got more of these in here. And

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so the length of

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this is much shorter versus if I have a much longer wavelength than the

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frequency is much lower,

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even though the wavelength is much higher or longer, if we want to think of it

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that way. In fact,

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there's a relationship between frequency and wavelength. If I multiply the

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frequency times the

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wavelength, and by the way, we measure the wavelength or represent wavelengths

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with the

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Greek letter lambda here, if I multiply these two together, I get the speed of
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Greek letter lambda here, if I multiply these two together, I get the speed of

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the wave form.

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Because this wave form is actually moving in free space at a particular speed.

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Well, what is the speed of a wireless wave form? Well, we already said it. It's

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light, so it's going

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at the speed of light. Meaning if I take a Wi-Fi or just ultimately any radio

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frequency wave form,

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and I multiply the frequency times the wavelength, I'm going to get the speed

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of light, which is a

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defined constant in the physics space, which I think is pretty cool. We just
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defined constant in the physics space, which I think is pretty cool. We just

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take any Wi-Fi frequency

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and multiply it by its wavelength. It will equal the speed of light. So all of

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this is cool, and I

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guess that I like to geek out on it, but at some point this has to bring us

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back to computer networking

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and specifically data. So where does the data come from in all of this? If I'm

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going to send these

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light waves back and forth to one another, how do we make them represent ones

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and zeros? And this

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is a fascinating conversation around data encoding within the wireless wave
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is a fascinating conversation around data encoding within the wireless wave

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forms. We can't dive into

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all the details that really exceeds the scope of this course, but what we'll

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find in wireless

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networking is that we are going to encode data into the wave forms using this

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process called

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modulation. And modulation is just a really fancy word that means changing. We

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're going to change

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the wireless wave forms a little bit. For example, I might send a waveform like
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the wireless wave forms a little bit. For example, I might send a waveform like

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this and this equals

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a zero. And then I might completely flip it around. This is called a phase

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manipulation. And I might

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say that this waveform equals a one. It's the same frequency. It's the same

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amplitude, but the phase

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is off where it starts and stops is going to be a little bit different. This

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waveform starts here,

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for example, if I look over here at the exact same spot where it starts, it's

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actually here in the

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middle. So it's a 180 degree phase shift. We just sort of shift it halfway. I
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middle. So it's a 180 degree phase shift. We just sort of shift it halfway. I

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might also change

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the amplitude. So maybe I could say that this waveform here is a zero, but then

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I'm going to take

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the exact same phase and the exact same frequency, but shorten the amplitude

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and say that this is a one.

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However, I decide to modulate and change is somewhat arbitrary. So long as the

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transmitter and

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the receiver, which could be either of these devices, could trade be transm

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itting in one direction or

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the other, either way, as long as they agree on what represents a zero, what
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the other, either way, as long as they agree on what represents a zero, what

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represents a one,

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and even more importantly, if we get to a point where I say I'm going to encode

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many bits in here.

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So I might say this is a zero, zero, zero, one versus a one, zero, zero, one.

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At this point, we have to

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be very careful to make sure that we agree on what the rules are for this

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communication. And so

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in the end, what we find is that by performing one of these transmissions, I

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want to send a 1,001.
WEBVTT
X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000

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want to send a 1,001.

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I send a very specific type of waveform to represent this. And the other device

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hopefully

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receives this well and says, ah, you sent me a 1,001. And that is thanks to the

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concept of data encoding

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using the modulation of these radio frequency waveforms.