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  • - [Presenter] For most of us,

  • a mobile phone is a part of our lives.

  • But I'm sure you're curious minds

  • have always been struck by such questions

  • as how a mobile phone makes a call,

  • and why there are different generations

  • of mobile communications?

  • (upbeat music)

  • Let's explore the technology behind mobile communications.

  • When you speak on your phone,

  • your voice is picked up by your phone's microphone.

  • The microphone turns your voice into a digital signal

  • with the help of MEMS sensor and IC.

  • The digital signal contains your voice

  • in the form of zeros and ones.

  • An antenna inside the phone receives these zeros and ones

  • and transmits them in the form of electromagnetic waves.

  • Electromagnetic waves transmit the zeros and ones

  • by altering the wave characteristics,

  • such as the amplitude, frequency, phase,

  • or combinations of these.

  • For example, in the case of frequency,

  • zero and one are transmitted

  • by using low and high frequencies respectively.

  • So, if you could find a way

  • to transmit these electromagnetic waves

  • to your friend's phone,

  • you would be able to establish a call.

  • However, electromagnetic waves

  • are incapable of traveling long distances.

  • They lose their strength due to the presence

  • of physical objects, electrical equipment,

  • and some environmental factors.

  • In fact, if there were no such issues,

  • even then, electromagnetic waves would not carry on forever,

  • due to the Earth's curved structure.

  • To overcome these issues, cell towers were introduced,

  • using the concept of cellular technology.

  • In cellular technology,

  • a geographic area is divided into hexagonal cells

  • with each cell having its own tower and frequency slot.

  • Generally, these cell towers are connected through wires,

  • or more specifically, optical fiber cables.

  • These optical fiber cables are laid under the ground

  • or the ocean,

  • to provide national or international connectivity.

  • The electromagnetic waves produced by your phone

  • are picked up by the tower in your cell

  • and convert them into high frequency light pulses.

  • These light pulses are carried to the base transceiver box,

  • located at the base of the tower

  • for further signal processing,

  • After processing, your voice signal is routed

  • towards the destination tower.

  • Upon receiving the pulses,

  • the destination tower radiates it outwards

  • in the form of electromagnetic waves,

  • and your friend's phone then receives the signal.

  • This signal undergoes a reverse process,

  • and your friend hears your voice.

  • So, it's true that mobile communications

  • are not entirely wireless,

  • they do use a wired medium too.

  • This is how mobile communications are carried out.

  • However, there was a big issue

  • that we intentionally left unanswered.

  • Mobile communication is only successful

  • when your tower transfers the signal to your friends tower.

  • But how does your tower know

  • in which cell tower area your friend is located?

  • Well, for this process, the cell tower gets help

  • from something called a mobile switching center.

  • The MSC is the central point of a group of cell towers.

  • Before moving further,

  • let's explain more information about the MSC.

  • When you purchase a SIM card,

  • all the subscription information

  • is registered in a specified MSC.

  • This MSC will be your home MSC.

  • The home MSC stores information such as service plans,

  • your current location, and your activity status.

  • If you move outside the range of your home MSC,

  • the new MSC, which serves you instead,

  • is known as a foreign MSC.

  • As you enter a foreign MSC region,

  • it communicates with your home MSC.

  • In short, your home MSC always knows

  • which MSC area you are in.

  • To understand in which cell location the subscriber is

  • within the MSE area,

  • the MSC uses a few techniques.

  • One way is to update the subscriber location

  • after a certain period.

  • When the phone crosses a predefined number of towers,

  • the location update is again done.

  • The last one of these is when the phone is turned on.

  • Let's try to understand all of these procedures

  • with an example.

  • Suppose, Emma wants to call John.

  • When Emma dials John's number,

  • the call request arrives at Emma's home MSC.

  • Upon receiving John's number,

  • the request will be forwarded to John's home MSC.

  • Now, John's MSC checks for his current MSC.

  • If John is in his home MSC,

  • the call requests will be immediately sent

  • to his current cell location,

  • and it checks whether John is engaged on another call,

  • or if his mobile is switched off.

  • If everything is positive, John's phone rings,

  • and the call will be connected.

  • However, if John is not in his home MSC,

  • John's home MSC simply forwards the call request

  • to the foreign MSC.

  • The foreign MSC

  • will follow the previously explained procedure

  • to locate John's phone,

  • and will then establish the call.

  • Now, let's discuss why the frequency spectrum

  • is quite important in mobile phone communications.

  • To transfer zeros and ones in digital communication,

  • each subscriber is allocated a frequency range.

  • However, the frequency spectrum available

  • for cellular communications is quite limited,

  • and there are billions of subscribers.

  • This issue is solved with the help of two technologies,

  • one frequency slot distribution,

  • and two, multiple access technique.

  • In the first technique,

  • different frequency slots are carefully allocated

  • to different cell towers.

  • In the multiple access technique,

  • this frequency slot is efficiently distributed

  • amongst all the active users in the cell area.

  • Now, the big question.

  • Why are there different generations

  • of mobile phone technologies?

  • 1G originally allowed users, for the first time,

  • to carry a phone without a cable attached to it.

  • But 1G suffered from two major problems.

  • The first problem was that the wireless transmission

  • was in an analog format.

  • Analog signals that are easily altered by external sources.

  • So, it provided poor voice quality and poor security.

  • The second problem was that it used

  • the frequency division multiple access technique,

  • which used the available spectrum in an inefficient way.

  • These factors paved the way for the second generation

  • of mobile communications,

  • 2G used digital multiple access technologies, namely TDMA,

  • or CDMA technology.

  • The second generation

  • also introduced a revolutionary data service, SMS,

  • and internet browsing.

  • 3G technology was focused

  • on giving a higher data transfer speed.

  • It used a WCD multiple access technique,

  • along with an increase in bandwidth.

  • To achieve this, the 3G speed of two Mbps

  • allowed the transfer of data for uses

  • such as GPS, videos, voice calls, et cetera.

  • 3G was a huge step in the transformation

  • of the basic phone to a smartphone.

  • Next came 4G, which achieved speeds of 20 to 100 Mbps.

  • This was suitable for high resolution movies and television.

  • This higher speed was made possible

  • due to the OFD multiple access technology,

  • and MIMO technology.

  • MIMO uses multiple transmitter receiver antennas

  • inside both the mobile phone and the towers.

  • The next generation of mobile communication, 5G,

  • to be rolled out soon,

  • will use enhanced MIMO technology and millimeter waves.

  • It will provide seamless connectivity

  • to support the internet of things,

  • such as driverless cars and smart homes.

  • Would you like to learn how a touchscreen works?

  • Please check out this video.

  • Please don't forget to subscribe to Learn Engineering,

  • and your support at patreon.com is invaluable.

  • Thank you.

- [Presenter] For most of us,

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How does your mobile phone work? | ICT #1

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    kt_joanna に公開 2021 年 07 月 17 日
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