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How does your mobile phone work? | ICT #1 - YouTube
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- [Presenter] For most of us,
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a mobile phone is a part of our lives.
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But I'm sure you're curious minds
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have always been struck by such questions
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as how a mobile phone makes a call,
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and why there are different generations
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of mobile communications?
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(upbeat music)
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Let's explore the technology
behind mobile communications.
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When you speak on your phone,
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your voice is picked up by
your phone's microphone.
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The microphone turns your
voice into a digital signal
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with the help of MEMS sensor and IC.
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The digital signal contains your voice
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in the form of zeros and ones.
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An antenna inside the phone
receives these zeros and ones
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and transmits them in the
form of electromagnetic waves.
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Electromagnetic waves
transmit the zeros and ones
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by altering the wave characteristics,
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such as the amplitude, frequency, phase,
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or combinations of these.
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For example, in the case of frequency,
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zero and one are transmitted
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by using low and high
frequencies respectively.
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So, if you could find a way
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to transmit these electromagnetic waves
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to your friend's phone,
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you would be able to establish a call.
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However, electromagnetic waves
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are incapable of traveling long distances.
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They lose their strength
due to the presence
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of physical objects, electrical equipment,
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and some environmental factors.
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In fact, if there were no such issues,
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even then, electromagnetic waves
would not carry on forever,
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due to the Earth's curved structure.
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To overcome these issues,
cell towers were introduced,
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using the concept of cellular technology.
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In cellular technology,
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a geographic area is
divided into hexagonal cells
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with each cell having its
own tower and frequency slot.
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Generally, these cell towers
are connected through wires,
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or more specifically,
optical fiber cables.
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These optical fiber cables
are laid under the ground
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or the ocean,
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to provide national or
international connectivity.
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The electromagnetic waves
produced by your phone
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are picked up by the tower in your cell
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and convert them into high
frequency light pulses.
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These light pulses are carried
to the base transceiver box,
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located at the base of the tower
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for further signal processing,
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After processing, your
voice signal is routed
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towards the destination tower.
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Upon receiving the pulses,
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the destination tower radiates it outwards
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in the form of electromagnetic waves,
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and your friend's phone
then receives the signal.
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This signal undergoes a reverse process,
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and your friend hears your voice.
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So, it's true that mobile communications
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are not entirely wireless,
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they do use a wired medium too.
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This is how mobile
communications are carried out.
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However, there was a big issue
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that we intentionally left unanswered.
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Mobile communication is only successful
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when your tower transfers the
signal to your friends tower.
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But how does your tower know
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in which cell tower area
your friend is located?
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Well, for this process,
the cell tower gets help
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from something called a
mobile switching center.
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The MSC is the central point
of a group of cell towers.
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Before moving further,
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let's explain more
information about the MSC.
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When you purchase a SIM card,
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all the subscription information
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is registered in a specified MSC.
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This MSC will be your home MSC.
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The home MSC stores information
such as service plans,
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your current location,
and your activity status.
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If you move outside the
range of your home MSC,
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the new MSC, which serves you instead,
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is known as a foreign MSC.
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As you enter a foreign MSC region,
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it communicates with your home MSC.
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In short, your home MSC always knows
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which MSC area you are in.
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To understand in which cell
location the subscriber is
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within the MSE area,
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the MSC uses a few techniques.
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One way is to update
the subscriber location
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after a certain period.
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When the phone crosses a
predefined number of towers,
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the location update is again done.
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The last one of these is
when the phone is turned on.
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Let's try to understand
all of these procedures
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with an example.
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Suppose, Emma wants to call John.
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When Emma dials John's number,
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the call request arrives
at Emma's home MSC.
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Upon receiving John's number,
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the request will be
forwarded to John's home MSC.
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Now, John's MSC checks
for his current MSC.
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If John is in his home MSC,
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the call requests will be immediately sent
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to his current cell location,
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and it checks whether John
is engaged on another call,
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or if his mobile is switched off.
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If everything is positive,
John's phone rings,
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and the call will be connected.
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However, if John is not in his home MSC,
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John's home MSC simply
forwards the call request
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to the foreign MSC.
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The foreign MSC
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will follow the previously
explained procedure
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to locate John's phone,
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and will then establish the call.
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Now, let's discuss why
the frequency spectrum
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is quite important in
mobile phone communications.
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To transfer zeros and ones
in digital communication,
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each subscriber is
allocated a frequency range.
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However, the frequency spectrum available
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for cellular communications
is quite limited,
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and there are billions of subscribers.
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This issue is solved with
the help of two technologies,
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one frequency slot distribution,
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and two, multiple access technique.
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In the first technique,
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different frequency slots
are carefully allocated
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to different cell towers.
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In the multiple access technique,
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this frequency slot is
efficiently distributed
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amongst all the active
users in the cell area.
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Now, the big question.
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Why are there different generations
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of mobile phone technologies?
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1G originally allowed
users, for the first time,
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to carry a phone without
a cable attached to it.
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But 1G suffered from two major problems.
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The first problem was that
the wireless transmission
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was in an analog format.
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Analog signals that are easily
altered by external sources.
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So, it provided poor voice
quality and poor security.
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The second problem was that it used
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the frequency division
multiple access technique,
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which used the available
spectrum in an inefficient way.
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These factors paved the way
for the second generation
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of mobile communications,
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2G used digital multiple access
technologies, namely TDMA,
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or CDMA technology.
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The second generation
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also introduced a revolutionary
data service, SMS,
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and internet browsing.
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3G technology was focused
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on giving a higher data transfer speed.
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It used a WCD multiple access technique,
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along with an increase in bandwidth.
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To achieve this, the 3G speed of two Mbps
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allowed the transfer of data for uses
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such as GPS, videos,
voice calls, et cetera.
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3G was a huge step in the transformation
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of the basic phone to a smartphone.
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Next came 4G, which achieved
speeds of 20 to 100 Mbps.
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This was suitable for high
resolution movies and television.
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This higher speed was made possible
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due to the OFD multiple access technology,
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and MIMO technology.
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MIMO uses multiple
transmitter receiver antennas
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inside both the mobile
phone and the towers.
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The next generation of
mobile communication, 5G,
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to be rolled out soon,
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will use enhanced MIMO
technology and millimeter waves.
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It will provide seamless connectivity
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to support the internet of things,
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such as driverless cars and smart homes.
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Would you like to learn
how a touchscreen works?
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Please check out this video.
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Please don't forget to
subscribe to Learn Engineering,
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and your support at
patreon.com is invaluable.
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Thank you.
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