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How WiFi and Cell Phones Work | Wireless Communication Explained


How many of us really understand what goes
on when you text your friend across the ocean and they get the ping, almost instantaneously! Allow me to entertain you with a little thought
experiment. When you press “send” on your favourite
messaging app, where’s your message really going? “Into the air,” you’d say, “like radio
waves..” But let’s back up a bit. When you press send on whatsapp, you’re
essentially sending instructions to your mobile processor via tiny copper wires on a printed
circuit board in your smartphone. Now, these instructions are essentially electrical
impulses, right? And electrical impulses are just electrons
flowing along the potential difference. How exactly does your message “jump” into
thin air from being electron flows in copper wires? At one stage you had a circuit board that
you could touch and feel (and even smell) and then suddenly you have radio waves in
the invisible part of the spectrum, flying away into thin air at light speed. What’s in between? What’s in between is this odd looking device:
It’s an antenna, which translates to a “pole” in Latin. An antenna is a metal-tongued voodoo device
that swallows electrical impulses and spits out radio waves. It is silent as the dead, but its screams
can be heard for miles. Specifically, a Wi-Fi antenna like in the
picture, screams at 2.4 GHz (2 billion beats per second!) and spits out waves of length
12.5 centimeters. Unlike visible light, these waves can pass
through walls, and even bend around the corners! How does an antenna produce radio waves? Before we answer this question, let’s take
a small detour. Do you remember the recent buzz in pop-science
about gravitational waves? They’re basically fluctuations in gravitational
field, propagating as radiant energy. Einstein’s general relativity predicted
their existence a hundred years ago, and we’ve only recently discovered them. Just like gravitational waves, electromagnetic
waves are fluctuations in electromagnetic field, propagating as radiant energy. And, not much unlike the story of gravitational
waves, the existence of invisible electromagnetic waves was predicted by Maxwell’s equations
well before their discovery by Heinrich Hertz! So, to produce radio waves, you need to create
fluctuations in electromagnetic field. And to create those fluctuations, you need
electrons moving around in a conductor! The act of radio wave synthesis is a carefully
choreographed, rhythmic dance of electrons in tiny copper wires. Like perturbations in still water that radiate
outward from the point of disturbance, the electron flows in an antenna cause perturbations
in electromagnetic field which radiate out into space like electromagnetic waves. When you press “send” on your favourite
messaging app, your mobile OS sets off a chain of events that ultimately encode the message
as a careful choreography of electron dance. This dance results in rhythmic ebbs and flows
in the electromagnetic field in the surrounding space, which radiate outward towards a cell
tower. The receiving antenna on the cell tower feels
these ebbs and flows on its conducting surface, inducing an electron dance very similar to
the one at the transmitter. This electron dance is again a set of electric
impulses in tiny copper wires, which are decoded by the hardware at the cell tower. The decoded information is then carried on
high-throughput cables for thousands of miles across countries, continents and even oceans
through Transatlantic communications cables or some other Submarine communications cables,
to a cell tower near your friend across the ocean. From the tower to your friend’s phone is
another wireless jump. And finally, your friend hears the familiar
ping. How does the phone know where the cell tower
is? It doesn’t, and it doesn’t need to! Your phone broadcasts your message in all
directions for anyone to listen to. But don’t worry, your message will be encrypted
and only the cell tower can decode your message. How does the cell tower know that the message
is from me? With every message you transmit, you also
include a code that uniquely identifies your device. That is how the cell tower knows it’s you. How does the cell tower differentiate between
messages from different phones? The phones all agree on a protocol to send
messages to the tower either at different times, different frequencies, different locations,
or using different codes. The best analogy I have for this is that of
a classroom. Imagine a classroom with a 100 students and
just one teacher. Now, if all the students start speaking at
once, the teacher cannot understand any of them. So, they agree on a protocol. If a student wants to speak, they raise their
hand and wait for the teacher to point to them. The student does not speak unless they are
asked by the teacher to speak. If multiple students raise their hands at
once, the teacher picks them out one by one so that only one student is speaking at any
point in time. The cell tower is the teacher, and the devices
are students. While students can speak at different times
to avoid interference, devices can speak at different times, different frequencies or
different codes to avoid interference. So, you’re telling me that the majority
of the communication is not really wireless? Yes! Unless you’re using a Satellite phone, wireless
communication is only used for two steps along the road: sender to tower-1, and tower-2 to
receiver. The communication between the cell towers
happens through ultra high speed communication cables underground. But, aren’t cables so out of fashion for
21st century? Why not use wireless all the way? Well, the cables we’re talking about here
like the Transatlantic communications cable are definitely very high-tech. They can carry terabytes of data every second,
and do not face the problem of interference nearly as much as their wireless counterparts. Also, you’ll need a lot of satellites to
cater to billions of users and their data needs if you want to go wireless all the way. And, launching satellites is really really
expensive. That’s it for today guys. We’ll meet you with an another interesting
video. Till then stay happy stay curious. And ya, don’t forget to like share and subscribe
this channel if you haven’t subscribed yet.

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