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General Knowledge for Kidsmocomi.com/learn/general-knowledge/
A few years a�er Alexander Graham Bell invented the
telephone in 1876, a couple of scientists independently
began doing research on sending electromagnetic
signals, similar to the ones used in a telephone, through
the air.
�e discovery of radio waves transformed communica-
tion around the world because people could send and
receive messages without the use of a wire. It would
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only be a matter of time before the radio and the telephone would be combined into the mobile phone.
A man named Jagdish Chandra Bose was a pioneer in
the eld of wireless communication. However he did
not believe in patenting his research because he be-
lieved that this scientic breakthrough should be avail-
able for all to take and
replicate. �is is why
Guglielmo Marconi is
o�en attributed with the
discovery of wireless technology. Before we learn about the
complex system of mobile telephone networks, we
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should understand how the most basic two-way radio
works. A two-way radio or walkie-talkie has a transmit-
ter to send radio signals and an antenna to receive
them.
A transmitter is the part of a device that has the ability
to change the frequency and amplitude of a wave into
an electromagnetic signal.
In this case it is a sound
wave.
�e antenna of another
walkie-talkie picks up this signal and converts it back
into a sound wave which we can understand. However,
this system is limited because it only allows you to
transmit information over 1 channel and only one Copyright 2012 Mocomi & Anibrain Digital Technologies Pvt. Ltd. All Rights Reserved. ©
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person can be talking at any given time since both talk-
ing and listening occur over the same channel.
Mobile phones are di�erent because they use 1 channel
to transmit and another one to receive. Before mobile
technology was developed the way it is today, there
were radio phones. �e radio-telephone system used
one radio tower that had 25 channels. �is antenna was
responsible for receiving signals from one radio-phone
and sending it to a desired destination.
walkie-talkie
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But the phones themselves were huge because they had
to be powerful enough to transmit and receive signals
for up to 70 kms.
A cellphone network avoids this problem by breaking
up this area into many pieces known as cells. Each cell
has its own radio tower that has a range of about 26
square kms. �ink of each cell as a hexagon placed
beside another hexagon, on a larger hexagonal grid.
Mobile
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Today, in 2012, we have phones and other hand-held
devices that allow you talk on the phone, upload photographs, download music and much more, but this
wasn't always the case. Let's see how this development
came about from the early days of wireless communica-
tion.
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1G refers to the rst generation of mobile communica-
tion technology. �is was an analog system that was
rst introduced in Japan by the Nippon Telegraph and
Telephone in 1979.
�e voice signal from the handset was was sent to a
tower at a high analog frequency.
1G
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�e tower would pick up this signal and convert it to
digital before transmitting it to another tower in the
area. �e second tower would locate the desired re-
ceiver, convert the digital signal back to analog, which
the handset would convert into sound waves.
Japan was very successful
in implementing this
technology and within
ve years it had become
the rst nationwide 1G
network.A single cell
tower in the 1G network had a very limited capacity
because each phone call used 4 channels at any given
time- 2 for listening at each telephone and 2 for talking.
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�is was not a very e�cient system and was not secure
because it used radio frequencies that cannot be easily
encrypted for the purpose of a phonecall. An added
problem was that when a signal moved out of the range
of one tower to another, calls would not be transferred
properly and would get disconnected.
You might be wondering
what exactly an analog
signal is, so before we
make the switch to digi-
tal, let's nd out.
An analog signal is a
continuous signal that
�uctuates i.e. it is always
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evolving and every point of the signal is signicant to
the information it is carrying.
�is means that every part of an analogue signal carries
important data that is di�erent to another point on the
same signal.
Digital data on the other hand is a bundle of informa-
tion that has to be unbundled before it can be interpreted.
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�e big breakthrough with 2G was that it was an en-
tirely digital network. �e 1G network used an analog
signal to connect with cellphone towers which limited
the range and the number of users that could be on a
call at any given time.
�e second generation
(2G) mobile communica-
tion system can be divided
into 3 parts- FDMA,
CDMA and TDMA, which
are basically di�erent ways
in which cellphones could
access the channels of a tower.
FDMA (Frequency Division Multiple Access)FDMA
2G
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was not the most e�cient of the three systems because
while it was able to handle digital data, it was simply a
more sophisticated way of transmitting analog signals.
It split a single channel into uniform pieces of band-
width and allowed multiple cellphones to access the
same channel through small
variations in frequency.
TDMA (Time Division Multiple
Access)One of the basic concepts
of mobile communication is to
allow multiple users to send and
receive information over 1 channel i.e. many people
could share the same bandwidth. Consider any 1 chan-
nel on a mobile tower which is able to send and receive
a xed amount of data per second. TDMA split this one
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second into three and allowed three di�erent users to
share each second of space on a channel. Network
speeds had risen greatly a�er making the switch from
analog to digital signals, which allowed for towers to
relay messages at a fraction of a second.
CDMA (Code Division Multiple Access)Instead of
breaking up the channels into smaller parts, the CDMA
system broke the information into smaller packets of
information. Using a unique spreading code, these
packets were spread over multiple towers along with in-
formation on its destination. Once all the packets
reached the destination tower, it was reassembled into
its original form and sent to the receiver in one part.
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�e third generation (3G) of mobile networking
systems o�ered a wider variety of services than what
came before and also increased the speeds at which in-
formation was relayed.
�e 3G network allowed people to download
information at 14.4 Mb per second and an upload speed
of 5.8 Mb per second. �is network opened the road to
accessing the internet on your mobile device and also
protecting the information you sent and received much
more e�ciently than the 2nd generation.
3G
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�ere is a current generation of a communication
network called the fourth generation (4G) that is still
in its development phase, although some countries
have begun implementing this technology already.
Usually the quality of
speed diminishes when
the location of the phone
is constantly moving. �e
4G system increases the
e�ciency of the network
by improving the antenna in your mobile
device without compro-
mising on design. It
boasts of greater internet
4G
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speeds on highly secure channels. �is new network
is allows people to use multimedia applications that
handle audio, video, and encrypted information with
very little loss of quality.
It took inventors around 100 years to combine the tel-
ephone and the radio into the mobile phone. However,
the advances in mobile phone networks have grown
leaps and bounds since the radio-phone was intro-
duced in the 1970's.
As wired telephones
slowly become a thing
of the past, mobile
phone are packed with
more and more features Copyright 2012 Mocomi & Anibrain Digital Technologies Pvt. Ltd. All Rights Reserved. ©
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as technology experts continually reduce the size of the
device while increasing its power and e�ciency. Mobile
phone technology is moving at a furious pace towards
creating a more connected world. �ese networks allow
us to connect with family living in other countries, it
helps scientists track important information about our
planet over vast distances, and basically makes our
large planet seem a little smaller and connected. So take
a good look at that tiny mobile phone in your hand and
know that this little piece of technology is changing the
way the world communicates and interacts.
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Project
Now that you know how wireless communication
works, go backwards and nd out how regular tel-
ephones (with wires) work. You can start by google the
words 'how a telephone works'.
Some phones, especially those made for the US market
cannot be used with sim-cards from outside the US.
Can you nd out why this is?
Using your amazing research skills, nd out about the
di�erent advances in radio that were put forth by
Nikolai Tesla and Guglielmo Marconi.
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