How does your mobile phone work

Humzzaa

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Transcript

00:00For most of us, a mobile phone is a part of our lives.

00:04But I'm sure your curious minds have always been struck by such questions as

00:08how a mobile phone makes a call

00:10and why there are different generations of mobile communications.

00:17Let's explore the technology behind mobile communications.

00:22When you speak on your phone, your voice is picked up by your phone's microphone.

00:26The microphone turns your voice into a digital signal with the help of a MEMS sensor and IC.

00:35The digital signal contains your voice in the form of zeros and ones.

00:42An antenna inside the phone receives these zeros and ones

00:46and transmits them in the form of electromagnetic waves.

00:51Electromagnetic waves transmit the zeros and ones

00:54by altering the wave characteristics such as the amplitude, frequency, phase or combinations of these.

01:03For example, in the case of frequency, 0 and 1 are transmitted by using low and high frequencies respectively.

01:11So if you could find a way to transmit these electromagnetic waves to your friend's phone,

01:21you would be able to establish a call.

01:24However, electromagnetic waves are incapable of traveling long distances.

01:28They lose their strength due to the presence of physical objects, electrical equipment and some environmental factors.

01:39In fact, if there were no such issues, even then, electromagnetic waves would not carry on forever due to the Earth's curved structure.

01:47To overcome these issues, cell towers were introduced using the concept of cellular technology.

01:58In cellular technology, a geographic area is divided into hexagonal cells,

02:03with each cell having its own tower and frequency slot.

02:07Generally, these cell towers are connected through wires or, more specifically, optical fiber cables.

02:15These optical fiber cables are laid under the ground or the ocean to provide national or international connectivity.

02:23The electromagnetic waves produced by your phone are picked up by the tower in your cell and convert them into high-frequency light pulses.

02:32These light pulses are carried to the base transceiver box located at the base of the tower for further signal processing.

02:40After processing, your voice signal is routed towards the destination tower.

02:45Upon receiving the pulses, the destination tower radiates it outwards in the form of electromagnetic waves,

02:52and your friend's phone then receives the signal.

02:55This signal undergoes a reverse process, and your friend hears your voice.

03:01So, it's true that mobile communications are not entirely wireless.

03:05They do use a wired medium, too.

03:08This is how mobile communications are carried out.

03:11However, there is a big issue that we intentionally left unanswered.

03:16Mobile communication is only successful when your tower transfers the signal to your friend's tower.

03:22But how does your tower know in which cell tower area your friend is located?

03:26Well, for this process, the cell tower gets help from something called a mobile switching center.

03:34The MSC is the central point of a group of cell towers.

03:39Before moving further, let's explain more information about the MSC.

03:43When you purchase a SIM card, all the subscription information is registered in a specified MSC.

03:52This MSC will be your home MSC.

03:55The home MSC stores information such as service plans, your current location, and your activity status.

04:01If you move outside the range of your home MSC, the new MSC which serves you instead is known as a foreign MSC.

04:10As you enter a foreign MSC region, it communicates with your home MSC.

04:15In short, your home MSC always knows which MSC area you are in.

04:20To understand in which cell location a subscriber is, within the MSC area, the MSC uses a few techniques.

04:27One way is to update the subscriber location after a certain period.

04:36When the phone crosses a predefined number of towers, the location update is again done.

04:42The last one of these is when the phone is turned on.

04:48Let's try to understand all of these procedures with an example.

04:53Suppose Emma wants to call John.

04:55When Emma dials John's number, the call request arrives at Emma's home MSC.

05:03Upon receiving John's number, the request will be forwarded to John's home MSC.

05:09Now, John's MSC checks for his current MSC.

05:14If John is in his home MSC, the call request will be immediately sent to his current cell location,

05:20and it checks whether John is engaged on another call or if his mobile is switched off.

05:25If everything is positive, John's phone rings and the call will be connected.

05:32However, if John is not in his home MSC, John's home MSC simply forwards the call request to the foreign MSC.

05:40The foreign MSC will follow the previously explained procedure to locate John's phone, and will then establish the call.

05:49Now let's discuss why the frequency spectrum is quite important in mobile phone communications.

05:55To transfer zeros and ones in digital communication, each subscriber is allocated a frequency range.

06:02However, the frequency spectrum available for cellular communications is quite limited, and there are billions of subscribers.

06:10This issue is solved with the help of two technologies.

06:14One, frequency slot distribution, and two, multiple access technique.

06:20In the first technique, different frequency slots are carefully allocated to different cell towers.

06:27In the multiple access technique, this frequency slot is efficiently distributed amongst all the active users in the cell area.

06:34Now the big question, why are there different generations of mobile phone technologies?

06:451G originally allowed users, for the first time, to carry a phone without a cable attached to it.

06:51But 1G suffered from two major problems.

06:55The first problem was that the wireless transmission was in an analog format.

07:00Analog signals are easily altered by external sources,

07:03so it provided poor voice quality and poor security.

07:07The second problem was that it used the frequency division multiple access technique,

07:12which used the available spectrum in an inefficient way.

07:17These factors paved the way for the second generation of mobile communications.

07:212G used digital multiple access technologies, namely TDMA or CDMA technology.

07:28The second generation also introduced a revolutionary data service, SMS, and internet browsing.

07:383G technology was focused on giving a higher data transfer speed.

07:42It used a WCD multiple access technique, along with an increase in bandwidth, to achieve this.

07:49The 3G speed of 2 Mbps allowed the transfer of data for uses such as GPS, videos, voice calls, etc.

07:593G was a huge step in the transformation of the basic phone to a smartphone.

08:04Next came 4G, which achieved speeds of 20 to 100 Mbps.

08:10This was suitable for high-resolution movies and television.

08:15This higher speed was made possible due to the OFD multiple access technology and MIMO technology.

08:23MIMO uses multiple transmitter-receiver antennas inside both the mobile phone and the towers.

08:30The next generation of mobile communication, 5G, to be rolled out soon,

08:35will use enhanced MIMO technology and millimeter waves.

08:40It will provide seamless connectivity to support the internet of things,

08:44such as driverless cars and smart homes.

08:49Would you like to learn how a touch screen works?

08:52Please check out this video.

08:54Please don't forget to subscribe to Learn Engineering,

08:57and your support at Patreon.com is invaluable.

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