How Information Travels Wirelessly

How Information Travels Wirelessly


[MUSIC PLAYING] All right, so in
this video we’re going to understand how
information travels wirelessly. And what I mean by
this is that we’re going to understand how devices
like Wi-Fi, wireless internet work. How things like radios,
say, in cars work. And how things like cellphones,
which definitely use wireless communication,
how they work. And the reason that we
can understand all these in one pretty short
video is that they all use the same principles
communication. And they all use
communication via waves. So waves is something we’re
all intimately familiar with. We know from childhood
that if we have say a lake, and someone throws a
rock into this lake, then the rock is going to cause
ripples to form in the lake. And the key point
about these ripples– what makes them called
waves– is that they move. They propagate. And because they propagate,
they can carry information out about the initial disturbance
that created them. For example, the way that you’re
listening to my voice right now is that your
speaker– this is a very poor drawing
of a speaker– but your speaker is moving. And your speaker is
creating sound waves. And what sound wave is just
regions of high and low density in the air. These are supposed
to be air molecules. And so these sound
waves reach your year. And your ear does some
complicated process to transcribe that into sound. But again, these waves–
this information transition is possible because
the waves propagate. Now, to understand how
all these devices work we’re going to have to
talk about something called electromagnetic,
or EM, waves. And the exact nature
of these waves is too complicated
to go into now, and it’s not important
for understanding this. But let’s just give
you some examples of waves you already know about
that are, in fact, EM waves. So light, for example, is
an electromagnetic wave. Microwaves use electromagnetic
waves to heat up food. X-rays, whenever
you go to the doctor and you get an
x-ray image taken, the waves that form
that image are x-rays. And lastly, of
course, radio waves are another special type
of electromagnetic waves. So how do we use waves
to transmit information? That’s what we’re going
to try to understand now. And before we do that,
we need to understand two characteristics
of waves, two ways that we can quantify what makes
one wave different from other. So if I consider this
way of that I have here, there are two things
that I can ask about it. One, I can ask how
large is this way? And to answer such a
question what I might do is I might simply
measure the difference between the maximum value
and the central value or the equilibrium point. And that is something we
call the amplitude in wave terminology. So let’s say that the amplitude
is A. So this distance is A. And obviously,
this distance is A. And the difference between
the peak and trough, called the peak
to peak distance, is equal to, obviously, 2
times the amplitude or 2A. So amplitude is a very
easy, very intuitive concept about how to characterize
how big a wave is. So the other concept that’s
important is called frequency. And frequency is just the
answer to the question how fast do cycles
of the wave go by. So by cycle I mean a
region like this of a wave. The basic unit of the way that
repeats, each one of these is a cycle. And basically frequency
is equal to the number of cycles that occur in a unit
time, let’s say, a second. So a wave that looks like this
has a much higher frequency than a wave that looks
like this, even though they have the same amplitude. So now that we understand what
frequency and amplitude mean, we can use these concepts
to transmit information. And the first way that
I’m going to tell you about how to do this is
called amplitude modulation. And this is what the AM
stands for in AM radio. So the basic idea is best
to see by this example. So say I have some signal. Maybe it’s a sound
signal or something else. Say I have some signal
that I want to send you, and that signal looks like this. So how do I send
you this signal? Well, just for
convenience– you’ll see why I do this
in a second– but I want to draw the
negative of the signal. So this is the signal
that I want to send you. And I want to send it to you
via an electromagnetic wave. So what I do is I send you a
way of a particular frequency. And I tell you to look for
waves of that frequency. And what I’m going
to do is I’m going to send you this wave where
I change the wave based on the signal that
I want to send you. So whatever the
signal is low, I make the amplitude of my wave low. And wherever the signals
I make the amplitude of my way of high. So here we have two
distinct pieces. This is signal. And this wave that
I’m sending you is called the carrier wave,
because it carries the signal. So to decode this
all you have to do is you have to look at how big
the wave is at any given point. And then you can
get to the signal that l I was trying to send you. So this scheme’s called
amplitude modulation. And it’s the one that’s
used in radios most often, AM radios specifically, to get
you the songs that you here, say, in a car when
you’re driving and listen to the radio. Now there’s AM and also FM. And you’ve probably
guessed by now that FM means
frequency modulation. So frequency modulation
is another way I can send you information. And of course, we can
use frequency modulation in the same way that I used
amplitude modulation to send you some like sound file. But what I want
to talk about now is how things like cellphones
use frequency modulation to send digital information. And what I mean by that is if
cellphones want to send to each other, or to wireless towers
that communicate with them, they want to send information
in the forms of 1’s and 0’s. And later they transmit–
some hardware in the cellphone translate those 1’s and 0’s
into text or sounds or whatever. But to do that what
we can simply do is we can agree that if your
cellphone and you receive a frequency that looks like
this, then you call that a 0. But if you receive a frequency
that looks like this, then you call that a 1. So if I want to send
someone a message, 1 0 1 1. All I do I send them
this signal in which I change the frequency. So I want to send a 1 first. So here’s a 1. Then I want to send a 0. So then I’ll send another 1. [INAUDIBLE] low frequency. Then I want to send another 1. So to decode this message,
all you have to do is you have to look
at different points, and you have to see
what’s the frequency here. Is it a 0? Or is it a 1? And so this idea, FM, is the
basis how digital communication takes place wirelessly. It’s actually called
something more complex, frequency shift keying. So these two concepts
that I’ve outlined for you guys, FM and AM,
constitute the majority of how information is traveled
via electromagnetic waves between wireless devices.

Comments

  1. Post
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    Oliver Fawcett

    I have a question. If some radio stations transmit information via frequency modulation and others transmit information via amplitude modulation. How do radio's that pick up these waves distinguish between different radio stations

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    TheAmazeer

    so much thanks you made it clear how information is sent on AM and FM modulation? does that mean that Fm modulation send only digital information ?

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    Phat Vu

    I just wonder how cell phone sent infomation to telephone stations. I mean the energy of cell phone is so much lower than telephone stations. How can telephone stations can get the wave infomation from cellphone ? Thanks you in advanced

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    Susil Sahoo

    If I click a picture in my smartphone, then send this picture
    To someone through internet. Then how the picture is converted to 1011100.

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    Julio Blind

    Can anyone help me please , I want to create something ( a chip or something else ) that It (the chip) can understand when I answer my phone? What is the difference between a electromagnetic wave with information and another without information ? And if we have 2 electromagnetic waves one with and one without information how can I find which one is with information ?

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    cooldude 4172

    So the FM wave is also transported by a carrier wave? In that case, does a higher frequency carrier wave imply larger data transfer rates?

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    Bojavis.

    What I don't understand is how are these waves transmitted from one computer to another, especially without any plug-in. It's like fucking magic!!?

  43. Post
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    KnownAsCLH

    No but how does the information stay in the wave and for how long and is this information stored some where ? And do different waves have sizes per frequency like you have a much stronger wave but at a higher or lower frequency. Ok you might have answered this i will go do my own research. Thank you for sharing what you have learned. It may help me in the future.

  44. Post
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    chonchol sabbir

    sorry but i want to ask a stupid question as i am not the student of science. just i am curious to know about that. you know the radio signal or radio wave, is that all already have in nature or we need to make it through device?

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    Ian RioT

    i was guessing waves were being used like binary code. man im a genius.lmao

    how are the waves manipulated to produce longer and shorter waves?
    is there a universal radio binary language?
    also to receive the wave and have it produce the sound or information do you have to have a program that knows how to translate the waves? if you dont have a preprogramed anttenna with binary wave reading installed does ur waves holding the frequencies produce nothing on the other end?

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    Jordan Rinella

    But how does images, files and our voice get get through those frequencies? We understand how it travels but how these signals actually contain audio and visual material is something i can not find an answer to.

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    rishwana sekar

    Im studying electrical engineering 1st year
    I have an idea for my project but i don't have any basic technical knowledge about that i tell u that idea if u know any thing about my idea u plzz guide me

    The idea is watch which can transmit the information of heart pumping rate of person who wear that.
    Example if the person is going alone in the road,suddenly he getting accident,then his heart pumping is attending abnormality….then the watch made to transmit locations and about his condition to top 5 conntects which is already saved …
    And call ambulance too
    So that he can survived …..

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    Banaja Dandasena

    But I need a complete video about the this. How information are travel through waves? How mobile or any device receive it?

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    3bodyZZ

    If you want to find the key to the universe think in terms of energy , Frequency and vibration – Nikola Tesla 1856 – 1943

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    Zezo

    I am in love with how you teach and simplify all of the problems the most of the student face your genius well done I hope all the teacher and professors out there learn from you

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    Daniel Wright

    Don't forget to say that when receiving the waves of FM the device that receives them decodes the waves from a already written library of numbers for each wave. So this is why its so fast, each wave is already programmed to read FM .This is why AM radio is not as good as FM As am does not decode it just reads the waves as a high or low pitch wave. The reason this is so important is people still don't understand how it works as a whole.

    So each radio depending on who created it, works with a already written program to decode each wave as a one or zero.

    If you only have a AM radio it does not have any prerecorded information in it so it just picks up the waves and send them to your speaker. We use to call it a echo machine as it would just echo wave sounds into your speaker.

    But FM will read the waves like zeros and ones depending on the burst of frequency of each wave. If its one short blast or wave, then its a one. if there is a relaxed wave its a zero. The higher the range for the wave, the higher the pitch, the lower the wave or the more relaxed the burst, the lower the pitch.

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    awandererTJ

    No you don't answer the question. The waves of WHAT? Sound is transmitted by air. What is carrying the EM waves through the 'empty' outer space for example?

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    Nox NC

    How come modulating the frequency doesn’t change the channel the device is tuned to? Isn’t it the frequency that determines what station you are listening to?

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    Dark Thoughts

    Yeah but what about PSK and the attributes of each method? Nice simple approach, but what if someone doesn't get the initial explanation?

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    Wei Pao

    That's really helpful!It took me less than ten minutes to understand the basic of wireless communication.

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    metitusable

    It's all fine and solid and it nakes sense if there was only one receiver and one transmitter but that's hardly the case. If two devices are sending radio waves at the very same frequency how do you how which is which?

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    A's Networks Technology & Electrical Contractor

    Thats been my question for tjehe last 5 years I mean I knew it had to been 0's amd 1's bit I didn't know if within the same wave but you're saying shorter waves are 0's and longer waves are the 1's????

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