I'm not going to lie, I am a little bit of a physics geek. Whenever we talk
about wireless
communications, I love drilling into the details of our wireless waveforms and
how we
encode the data. It's pretty fascinating technology. Now within the scope of
this conversation
and this exam, we're going to be looking at things from the perspective of
being a wireless
network engineer, which is usually going to focus a little bit more on wireless
design
and making sure we understand how a lot of our wireless communications happen, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
and making sure we understand how a lot of our wireless communications happen,
wireless topologies infrastructure, those kinds of things. But at the heart of
wireless communications,
we do need to understand that we are leveraging this concept of radio frequency
, which is abbreviated
as RF. And the question I love to ask is what exactly is radio frequency? If I
've got an access
point here and I've got a mobile device and they're communicating back and
forth, I mean, what
exactly are these waves that they're sending wirelessly? The reality is that WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
exactly are these waves that they're sending wirelessly? The reality is that
this word radio is
kind of unfortunate. We use the word radio to describe something I'm listening
to. And so as
such, we typically are inclined to think that maybe radio frequency is a sound
thing and nothing
could be further from the truth. Radio has nothing to do with sound. In fact,
it has to do with maybe
what we might consider to be the opposite of sound, which is that radio WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
what we might consider to be the opposite of sound, which is that radio
frequency is actually a form
of light. Yes, it's a form of light. When we say that we're communicating to
one another,
these two devices are essentially blinking light at one another. Now
interestingly, this light
is light that we cannot see. So it's unseen light. It exists outside the range
of frequencies that
our eyes can detect. And furthermore, because it is a different set of
frequencies, it's actually
much lower than the light that we see. They can also pass through walls and WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
much lower than the light that we see. They can also pass through walls and
obstacles and all
kinds of things. So it doesn't behave like we might expect light to behave in
some ways. And yet,
light reflects off of mirrors and radio frequency reflects off of mirrors,
reflective surfaces,
these kinds of things. So it shares some properties. It doesn't share other
properties. And yet,
we compare divisible light and yet underlying all of this, it really is just a WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
we compare divisible light and yet underlying all of this, it really is just a
form of light.
And so what we do to describe a waveform is we draw it out like this. This is
what a wireless
waveform looks like. And if you've ever taken a physics class, maybe you had
one person stand on one
end of a jump rope and the other person stand on the other end and you swing
this up and down and
forms these wave forms in the middle. Wave forms exist not just for light rays
or light waves, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
or light waves,
but also it exists in the form of sound waves and jump ropes and all kinds of
things. So we're going
to see these types of wave forms in a lot of places. This specifically is known
as a sinusoidal
waveform. And that's distinguished from things that we might see elsewhere like
a square wave.
We've got all kinds of other waveforms that might exist, but light is very
analog in nature and it
is sinusoidal as a result. Now there's a lot of parts of the waveform that we WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
is sinusoidal as a result. Now there's a lot of parts of the waveform that we
probably don't need to
know necessarily as part of this course, but it's helpful to know. For example,
we see peaks and
valleys. These peaks and valleys have words that we used to describe them. For
example, we have
the crest and the trough at the top and bottom. We also have the waveform
oscillating around a
middle point that we refer to as the origin. And we might also, and this part
is important,
is fine that there's a level of energy at every point along the waveform. And WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
is fine that there's a level of energy at every point along the waveform. And
this level of energy
is described as the amplitude when it's at its peak. So this much energy right
here, or for that
matter, this much energy down here is considered to be the amplitude. The more
energy a waveform has,
the greater its amplitude. We might see smaller waveforms like this that have
much lower energy or
waveforms that do this that have a much higher energy level. So while that's WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
waveforms that do this that have a much higher energy level. So while that's
interesting, the crest,
the trough, the origin, they don't really help us out a lot with wireless
communications, at least
within the scope of this conversation. But instead, what we need to focus on a
lot is going to be
a couple of other elements, namely the frequency, which is right there in the
word radio frequency,
and our wavelength. Now, frequency is defined as the number of oscillations or
modulations in a given
time period. So we're talking about essentially the number of waves per second. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
time period. So we're talking about essentially the number of waves per second.
As this waveform
travels, we can actually measure the amount of time it takes for us to repeat
ourselves,
because these waveforms are going to continue to repeat over and over again.
And so it's really just
a matter of finding a snippet right here in the middle where we say, okay, how
long did this take for
us to oscillate? If we are measuring it in time, we have a word for this. This WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
us to oscillate? If we are measuring it in time, we have a word for this. This
is the period. How long
it takes for one waveform to complete? But then we have this concept of
frequency that now is saying,
okay, but how many of these exist within a one second time period? And in this
case, we see that
we have three different waveforms inside of one second. So we have a fun unit
of measurement for
the frequency. It is known as the hertz, which is actually named after somebody WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
the frequency. It is known as the hertz, which is actually named after somebody
. And so anytime we
have a unit of measurement, we name it after someone, we typically capitalize
it. So we abbreviate
this as a capital H lowercase z. It does sound like we're talking about
something plural, but it's not
plural. It's just somebody's name ends with a z. So if I have one waveform in a
second, I would
indeed say that it's one hertz, not like one hertz or something like that. In
our case here, we say
we have three waveforms in one second. And so this means that we have a WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
we have three waveforms in one second. And so this means that we have a
frequency of three hertz.
Now, this is a very low frequency. If I want to talk about wireless
communications, we're usually
talking about potentially killer hertz or more often times megahertz and even
gigahertz.
So killer hertz, this would be a thousand. If I said it's one killer hertz, it
's a thousand hertz.
A megahertz, this is one million. And yes, a gigahertz is one billion. And this WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
A megahertz, this is one million. And yes, a gigahertz is one billion. And this
is typically the
range that our Wi-Fi communications are going to communicate in. So if we are
communicating at five
gigahertz, we're truly squeezing five billion waveforms into a single second,
which is pretty
incredible. Now, here's the crazy thing. If we want to talk about Wi-Fi, we're
talking about gigahertz.
If we want to talk about visible light, meaning the light that we can see red
and blue and green and WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
and blue and green and
all the beautiful colors that exist out there, then we are actually talking
about the
terror hertz range. And not just the terror hertz, but usually hundreds of
terror hertz. So for
example, we might be talking about 400 terror hertz for seeing visible light
that's actually at
the lower end of the spectrum that we can see. And that is talking about 400,
000 gigahertz.
So that is the difference between visible light and Wi-Fi and why Wi-Fi is so WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So that is the difference between visible light and Wi-Fi and why Wi-Fi is so
much lower frequency
than even what we see from a visible light perspective. Now, if we want to talk
about going to the
doctor and getting X-rays, that's even higher frequencies than visible light.
And we have to be
careful with the higher frequencies because that's where we can see radiation
causing us damage
as human beings. But anything lower than visible light is considered safe,
which is why we use the
lower light ranges for our wireless communications. Now, if we flip frequency WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
lower light ranges for our wireless communications. Now, if we flip frequency
around, we're going to
find that we have another unit of measurement, which is the wavelength. The
wavelength of a wave
form is truly the length that's right there in the name. We can measure this in
feet or inches or
more likely in meters and millimeters and nanometers. So the amount of distance
up here of one of our
cycles, this length, or again, the distance is what the wavelength is. And so WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
cycles, this length, or again, the distance is what the wavelength is. And so
we're typically again
talking about this in terms of nanometers, especially as it relates to anything
in the Wi-Fi space.
But if we're talking about much lower frequencies, then we get much longer
wavelengths. This is
an inversely proportional relationship inversely proportional, meaning that if
we increase the
frequency, the wavelength goes down because I've got more of these in here. And WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
frequency, the wavelength goes down because I've got more of these in here. And
so the length of
this is much shorter versus if I have a much longer wavelength than the
frequency is much lower,
even though the wavelength is much higher or longer, if we want to think of it
that way. In fact,
there's a relationship between frequency and wavelength. If I multiply the
frequency times the
wavelength, and by the way, we measure the wavelength or represent wavelengths
with the
Greek letter lambda here, if I multiply these two together, I get the speed of WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Greek letter lambda here, if I multiply these two together, I get the speed of
the wave form.
Because this wave form is actually moving in free space at a particular speed.
Well, what is the speed of a wireless wave form? Well, we already said it. It's
light, so it's going
at the speed of light. Meaning if I take a Wi-Fi or just ultimately any radio
frequency wave form,
and I multiply the frequency times the wavelength, I'm going to get the speed
of light, which is a
defined constant in the physics space, which I think is pretty cool. We just WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
defined constant in the physics space, which I think is pretty cool. We just
take any Wi-Fi frequency
and multiply it by its wavelength. It will equal the speed of light. So all of
this is cool, and I
guess that I like to geek out on it, but at some point this has to bring us
back to computer networking
and specifically data. So where does the data come from in all of this? If I'm
going to send these
light waves back and forth to one another, how do we make them represent ones
and zeros? And this
is a fascinating conversation around data encoding within the wireless wave WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
is a fascinating conversation around data encoding within the wireless wave
forms. We can't dive into
all the details that really exceeds the scope of this course, but what we'll
find in wireless
networking is that we are going to encode data into the wave forms using this
process called
modulation. And modulation is just a really fancy word that means changing. We
're going to change
the wireless wave forms a little bit. For example, I might send a waveform like WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
the wireless wave forms a little bit. For example, I might send a waveform like
this and this equals
a zero. And then I might completely flip it around. This is called a phase
manipulation. And I might
say that this waveform equals a one. It's the same frequency. It's the same
amplitude, but the phase
is off where it starts and stops is going to be a little bit different. This
waveform starts here,
for example, if I look over here at the exact same spot where it starts, it's
actually here in the
middle. So it's a 180 degree phase shift. We just sort of shift it halfway. I WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
middle. So it's a 180 degree phase shift. We just sort of shift it halfway. I
might also change
the amplitude. So maybe I could say that this waveform here is a zero, but then
I'm going to take
the exact same phase and the exact same frequency, but shorten the amplitude
and say that this is a one.
However, I decide to modulate and change is somewhat arbitrary. So long as the
transmitter and
the receiver, which could be either of these devices, could trade be transm
itting in one direction or
the other, either way, as long as they agree on what represents a zero, what WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
the other, either way, as long as they agree on what represents a zero, what
represents a one,
and even more importantly, if we get to a point where I say I'm going to encode
many bits in here.
So I might say this is a zero, zero, zero, one versus a one, zero, zero, one.
At this point, we have to
be very careful to make sure that we agree on what the rules are for this
communication. And so
in the end, what we find is that by performing one of these transmissions, I
want to send a 1,001. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
want to send a 1,001.
I send a very specific type of waveform to represent this. And the other device
hopefully
receives this well and says, ah, you sent me a 1,001. And that is thanks to the
concept of data encoding
using the modulation of these radio frequency waveforms.