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Science and Technology
The Nature and Development of Science and Technology
Case study – The important issues of science and technology
Case 4: Telephone communication
Activity and case-based learning & teaching resources
Students’ version
Table of Content (Students’ version)
Outline
Aims of study
Scheme of work
Background information
2
2
3
Teaching Resources
Lesson 1, 2
Background
Activity 1: Worksheet of game
Activity 2: Worksheet of experiment
Additional background information
Extended readings
4
4
4
5-6
7
8
Lesson 3, 4
Background
Activity 3: Science experiment
Additional background information
Extended activity
9
9
10 - 11
12 - 14
15 - 17
Lesson 5, 6
Background
Activity 4: Worksheet of technology demonstration
Additional background information
18
18
18- 20
21- 22
1
Students’ version
Outline
Aims of study
The aim of these lessons is to introduce an important scientific development – telephone
communication to students. Students can understand the contribution of scientists in pursuing a
faster and better communication method from understanding the ways that ancient people
communicate with each other and the invention process of the telephone. Nowadays, the
technological development of modern society is becoming more and more advanced and we can
easily communicate with people all over the world. Students should manage the newest and the
most useful ways of communication, so as to keep in pace with the technological development of
the society.
Scheme of work
Lessons Learning objective
1, 2



3, 4




5, 6


Teaching strategy
How did ancient people

communicate?

What would our lives be
without telephone

communication
technology?
Understand the contribution
of scientists to telephone
communication
development.
How do telephones
operate?
What are the elements
contributed to the invention
of telephones?
How was telephone
invented?
Are there any social or
political factors affecting
the development of this
kind of technology?
What are the modern
telephone communication
development techniques?
What are the means applied
for information


Learning and
teaching resources
Game: Pass a message on  Links of articles
Simple experiment of

PowerPoint
communication

Worksheet of the
Group discussion (living
game
without telephone

Worksheet of the
communication technology
experiment

Extended
activity
Story: The invention of
telephone by A.G. Bell
Science experiment







Explanation of the modern
technological development
Demonstration of the latest
technology
Group discussion (Network



Worksheet of the
experiment
PowerPoint
Links of articles
Extended
activity
PowerPoint
Links of articles
Extended
activity
2
Students’ version
transmission?
of people)
Background information
Do you know what is the first conversation transmitted through telephony? The inventor of
telephone is Alexander Graham Bell. In 10th March 1876, he called his assistant Thomas Watson,
“Mr.Watson- Come here- I want to see you.” (Adapted from Bell’s personal notes at
http://memory.loc.gov/mss/magbell/253/25300201/0022.jpg) If you were Bell, what would you
say?
In the recent 100 years, the development of telephone communication has progressed greatly.
The communication methods used by ancient people were elementary and simple. Igniting signal
fire is a common example. The constraints of this communication method are the distance of
transfer and the accuracy of information since the users could not ensure whether there is any
delay or error during message transmission, as the sender and receiver were not in direct
information transfer..The modern method of information transmission we are using is by written
records through individuals or letters by dove to the destination. Using written records is a more
reliable method for information transmission, so it is still widely used nowadays. However,
people tried to invent new technologies for improving living quality and hope it will bring the
communication technology into a new era.
Many inventors believed that voice messages could be transmitted through wires. Bell made
a telegraph for the experiment and finally, he found out the way of voice reproduction from the
inspiration of a malfunction telegraph. Finally he invented the mouthpiece and earpiece and
received the patent right on 7th March 1876.
Afterwards, the development of telephones went on extensively and their functions became
very versatile. The application of microwaves also induced breakthrough to the development of
telephone technology. Firstly, the introduction of indoor wireless telephones and then followed by
the mobile phones. We can use telephone for chatting, receiving information and even for seeking
emergency help (such as 999 service in Hong Kong). Moreover, telephones can be used for
unidirectional communication such as for paying bills and video communication.
We might ask ‘What are the factors leading to the rapid development of telephone
technology?’ The simplest answer is inevitably people’s in pursuance of quality living. Virtually,
the military contest among countries is also one of the main reasons. For example, the United
States needed transmitting information accurately and effectively during the Second World War,
so the government put a huge amount of money at communication facilities to enhance the
military strength of the nation.
Although telecommunication is developing rapidly, do you think it will entail other
problems while giving convenience to us? These included inter-personal relationship and security
issues. Students should spend more time to think about the problem when studying the history of
telephone development during the lessons.
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Students’ version
Teaching Resources
Lesson 1, 2: How did ancient people communicate with
each other?
Background
Have you ever been to the Great Wall in China? The Great Wall has a history of about 2000
years and all of the states of the lords have started constructing the walls ever since the period of
Spring, Autumn, and Warring States. Until 221 BC, the First Emperor of Qin Dynasty unified
China and started to construct and rebuild a new Great Wall massively to fend off the invasions
from the Xiong Nu (Huns) in the north. There are scattered outposts and watchtowers at the
higher position of the Great Wall, and some of them are used for generating smoke and fire
called ‘Feng Huo Tai’ (the outpost of fire signalling). When the soldiers in the outposts found the
presence of enemies, they would send out signals. They generated smoke during daytime and
igniting fire at night. When the soldiers at distant outposts observed the smoke and fire, they
would immediately generate it so the signal could be transmitted consecutively. The information
would then be transmitted to the commanding units at a faster speed. It was one of the ways
for communication in the ancient time, which is so different from the communication
methods nowadays.
Activity 1: Game (Pass a message on)
How do people communicate with each other before the development of advanced
telecommunication technology? Told from the history, we know that we can generate
smoke and fire for sending out alarming signals, we can transmit a word message by
doves, etc. But how about the time before the word characters were created? Is it reliable
by just relying on direct transmission among people?
Rules of the game:
1. Each group comprises about 7 – 8 students and line up in a straight line.
2. The first student in each group has to come out and remember the paragraph spoke by
the teacher. Students are not allowed to use paper and pens to take notes.
3. The teacher will repeat the paragraph once or twice to ensure students have
remembered the content.
4. When the teacher announces to start, the first student has to tell the content of the
paragraph to the second one. Then the second student would tell the third one
consecutively.
5. After all groups have finished the game, the last student in each group has to give the
answer about what they have remembered and marks are given by the teacher.
6. The time limit is 7 minutes, even if the whole message has not been passed to the last
student, he still has to tell the answer.
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Students’ version
Activity 2: Simple experiment of communication
Use a string to link up two paper cups can make you understand the basic principles
behind telephones easily. Through the vibration of string, sound can be transmitted from
one side to another side.
Students should try to figure out the factors affecting the information transmission and
reception ability of the primitive telephone. Students can think of the substances, the
length, the tightness and the thickness of the linking medium, etc. Then conduct simple
experiments to verify their effects on the ability of information receiving and transmission.
Students can use the table below to record the experimental results.
Observation
Assessment of information receiving capacity (highest quality: 5 points, high: 4 points,
general: 3 points, weak: 2 points, poor: 1 point)
Matters
Assessment of information receiving
capacity
Hemp string
Nylon string
Copper wire
Others
Length
Long hemp string
Short hemp string
Long copper wire
Short copper wire
Others
Tightness
Loose hemp string
Tight hemp string
Loose copper wire
Tight copper wire
Others
Thickness
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Students’ version
Thick-loose hemp string
Thin-tight hemp string
Thick-loose copper wire
Thin-tight copper wire
Others
Summary
Based on the above observation, can students summarize the effects of the different factors
above on the primitive telephone’s reception and transmission capacity?
The effects on reception and transmission
Matters
Length
Tightness
Thickness
Other factors
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Students’ version
Additional Background information:
In the 21st century, phones have become the necessities for communications between people. We
can easily chat and transfer information either with relatives living afar or with the schoolmates
living next to us by picking up the phone. Accompanying with the continue improvement and
development of telephone, general household phones have been developed into indoor wireless
phones and mobile phones. Telecommunication companies also supply long distance call service
and video conferencing service, all of which rest on the technological development.
However, what are the methods for people to communicate before the invention of telephone?
1. Igniting the signal fire
Ancient people would ignite signal fire to generate fire and smoke signals to notify people
located far away. This method is well known especially when performing military operations.
While discovered the enemies were coming or someone was in danger, the signal fire can be used
for communication and let the soldiers get ready to fight with the enemies. But the signal might
fail to transfer when signals were messy or the weather was not good for vision.
2.Beating drums to transmit sounds
The principle is similar to igniting the signal fire, but it relies on sound transmission to generate
signals for notifying distant people. If the route of transmission is not open enough, the obstacles
may block the sound transmission and reduce the effectiveness.
3. Writing letters
Letters have become one of the important and effective communication tools since the invention
of papers. Doves were firstly used for carrying letters and later post offices appeared which
increased the efficiency of sending letters. Citizens’ letters are collected first and then
dispatching according to districts. This method is more systematic than point-to-point
transfer. Nowadays, letters still play an important role although different communication methods
have been arisen in the society.
Up to the 19th century, Morse proved the feasibility of using telegraph for communication and it
brought about the new breakthrough of communication development. Scientists believed that as
information can be transmitted through electrical wires, it should also be feasible for transferring
voices and sounds. The idea of inventing telephones was initiated then.
Message of Morse Telegram
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Students’ version
Extended activity:
Through the explanation during the lessons, students should have understood more about the
communication methods in the past. Before the invention of telephones, the communication
among people was affected by many constraints and limitations. After the appearance of
telephones, it brought more convenience to us and it is the milestone of human communication
services.
If we were living in a society without electricity, all of the high-tech inventions would fail to
function due to lacking electric power. Can students imagine an effective method for
communication? Please try to explain your ideas by drawing and write down its operating
principles.
Figure：
Principle：
8
Students’ version
Lesson 3, 4: How do telephones operate?
Background
The invention of machines not only makes people’s lives become more convenient, but also
raises the quality of life. Among these inventions, telephones facilitate our lives the most. Who
invented telephones? It was by the scientist Bell. Bell noticed the prevailing telegram at that time
relied on wires to transmit electric waves. As a researcher of acoustics, he thought‘Why we
cannot use wires to transmit sound?’This idea initiated in his mind on inventing sound
transmitting device through electric waves, which was the telephone.
Telephone is a device we can hardly live without in our daily lives. We can easily use
telephones to communicate and contact with family and friends and transmit our messages
instantly. Due to the rapid technological development, we can keep in contact with relatives
overseas too. Telephone is the pioneer of modern and advanced technology, which finally
invented by Bell with his industrious effort. It also made a record in the history of communication
development.
Activity 3: Science experiment
Did Alexander Graham Bell invent telephones? The answer may either be ‘right’ or
‘wrong’. Although Bell has received the rewards finally, but some of the other inventors
also had contributions to telephone invention. Bell in Boston and Elisha Gray in Chicago
have had the desire to invent telegram that can transmit series of telegraphic wave signals
in single communication line, but neither of them succeeded. (This problem was then
solved by another inventor Edison) However, Bell and Gray have shifted to researches of
telephone at nearly the same time. They have also requested for the patent right on the
same day (14 February 1876) at the Patent and Trademark Office (PTO) of the United
States. However, Bell was earlier than Gray for a few hours and the patent right was
conferred to Bell (PTO No. 174465). This may be the most valuable patent right since the
introduction of patent right registration. Bell and his colleagues immediately shifted the
aim of their work centre from development of telephones to perfect and promote their
invention.
1. Objective
In this activity, students would become young scientists. They are asked to use some
simple equipment to make a model of telephone network. While communicating with
classmates, they would get hold of the principle of the telephone operation.
2. Theory
When we speak to the mouthpiece the sound wave transmitted in the form of
longitudinal waves would induce changes in the spacing of air molecules. The denser
region is the compressed air of high pressure and the looser region is the expanded air of
low pressure. The change in pressure leads to the forward and backward vibration of the
aluminium diaphragm at the speaker. When the carbon granules of the graphite
contacting plate are compressed with increased density, the resistance reduced and
results in higher electric current. When the density of carbon granules are lower, the
resistance increased and the electric current reduced. This phenomenon shows the
loudness and the frequency of voice would affect the strength of current flow when we
are talking on the phone. As a result, the magnetic field of the electromagnet in the
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Students’ version
earpiece would have the same fluctuation in its strength and frequency.
When the iron made-diaphragm in the earpiece is affected by the magnetic field of
electromagnet, it would be attracted and expelled to generate vibrations and emit sound
waves with comparable strength and frequency with the mouthpiece. The principle of
telephone earpiece is just like a loudspeaker.
Moreover, the earpiece (loudspeaker) can also be used as the mouthpiece, which can be
demonstrated by the experiment below.
3. Materials and apparatus (Each group)
4 loudspeaker
4 electric wires
A pair of scissors
Diagram of experimental apparatus connection:
Loud-
speaker
Loudspeaker
Loudspeaker
(Mouthpiece)
(Earpiece)
(Mouthpiece)
Loudspeaker
(Earpiece)
9V
battery
Loudspeaker
Loudspeaker
Loudspeaker
Loudspeaker
(Earpiece)
(Mouthpiece)
(Earpiece)
(Mouthpiece)
(a) No batteries are used
(b) 9V battery is (speake
used
r)
4. Experiment procedures
a. No batteries are used（as shown in figure a）
Cut the electric wires of 4 loudspeakers and remove the surface layer at two ends to
expose the copper wires. Use the wires to connect according to figure (a). The
distance between each loudspeaker is about 1 m. According to the figure, each
student use two loudspeakers where one is the mouthpiece and one is the earpiece.
Students should investigate its clearness and increase the distance between
loudspeakers to record the results.
b. 9V batter is used（as shown in figure b）
Keep on using the connection methods in figure (a), but use 9V battery in the wires.
Students should investigate the clarity and increase the distance between
loudspeakers to record the results.
Why loudspeakers can be used as both the mouthpiece and the earpiece?
When we speak to the mouthpiece, the sound wave transmitted would induce changes
in the spacing between air molecules. The denser region is the compressed air of high
pressure and the looser region is the expanded air of low pressure. The change in
pressure leads to the forward and backward vibration of the aluminium diaphragm at
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Students’ version
the earpiece, and then a weak current flow is induced.（Faraday’s Law）。
Information recording sheet
Experiment results(highest quality: 5 points, high: 4 points, general: 3 points, weak: 2
points, poor: 1 point)
Equipments \ distance
1m
3m
5m
10 m
a. Use 2 loudspeakers and speakers
b. Use 4 loudspeakers
c. Use 2 loudspeakers
Analysis and explanation
1. Try to explain why the experiment can still be conducted without the power source?
＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿
＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿
＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿
2. What is the effect of the distance between loudspeakers to the clarity of receiving sound?
Why?
＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿
＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿
＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿
3. Is there any difference on the signal transmission by the use of batteries?
＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿
＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿
＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿
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Students’ version
Additional background information:
How were telephones invented?
Various inventors believed that sounds could be transmitted through wires, they endeavoured to
investigate into it then. The first inventor who succeeded to produce telephones according to this
principle was a language teacher in Boston of Massachusetts - Alexander Graham Bell with
Scottish origin.
Bell made a telegraph to carry out his experiment. One day, the components in the machine
loosened and its operation was abnormal then. Bell was inspired from this incident and founds
out the way to copy the sound for transmission to distant places. The mouthpiece and earpiece
were invented as a result and the patent was awarded on 7 March 1876.
How do telephones operate?
Telephone could convert the sound and data into electrical energy and then transmit to distant
places. When we are speaking to the mouthpiece, the sound wave transmitted in the form of
longitudinal waves would induce changes in the spacing of air molecules. The denser region is
the compressed air of high pressure and the looser region is the expanded air of low pressure. The
change in pressure leads to the forward and backward vibration of the aluminium diaphragm at
the speaker.
When the carbon granules are compressed with increased density, the resistance reduced and
results in greater electric current. When the density of carbon granules are lower, the resistance
increased and the electric current reduced. This phenomenon shows the loudness and the
frequency of voice would affect the strength of current flow when we are talking on the phone.
As a result, the magnetic field of the electromagnet in the speaker would have the same
fluctuation in its strength and frequency.
Carbon
particles
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Students’ version
What are the functions of telephones?
The functions of telephones are very extensive. We can use telephones for chatting, handling
commercial business and even for seeking emergency help (such as 999 service in Hong Kong).
Moreover, telephones can be used for unidirectional communication such as for paying bills (the
caller use phones to communicate with distant computer system of the bank) and pick up the
messages in the telephone message box.
How does the sound transmitted by the telephone?
A basic telephone includes: a microphone to transmit the voice of the caller, a speaker equipped
with an electric signal amplifier, a dialling plate or buttons of digits, bell sound or alarm and is
called the set of electrical accessories called anti-side tone network which is for avoiding the
telephone speaker to receive too loud the sound from the caller.
Earpiece
Speaker
(speaker)
Touch-Tone
Keypad and Frequency
Generator
Ringer
Duplex cell
Mouthpiece
Microphone
(microphone)
Hook switch
to wall jack
From the figure above, three very simple components of telephones are shown:

A switch for connecting and interrupting the linkage of telephone and its circuit network.
When the handset is taken up, the phone is connected automatically.

A speaker with the size of a 50 cents coin.

A loudspeaker. The most primitive loudspeaker composed of carbon granule pressed in
between two very thin metal sheets. When sound travels through the loudspeaker, the
resistance of carbon granules would change with the alternations of sound wave
compression that resulted in adjustment of the electric current flow.
The operation of indoor wireless telephones
Indoor wireless telephone can be used in anywhere at home and even at the outdoor garden,
which allows speaker to walk around freely. Before the popularisation of mobile phones, indoor
wireless phones already make people feel free to chat with others at home. Nowadays, indoor
mobile phone can process three people conference, indoor messenger call and hand free devices,
etc.
Same as two-pieces telephone, indoors wireless phone consists of two main parts, the handset and
the base part. It has unified the functions of telephone and the radio receiver and substituted
two-pieces phone by the use of radio wave to connect the handset and the base part. However, the
wire connecting the base part with the telephone cable is still retained. The user may walk around
within a specified area of signal transmission as a result. The handset and the base part rely on the
coordination of a pair of frequency called the duplex frequency to guarantee speaking and
receiving can occur simultaneously.
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Students’ version
The operation of mobile phones
The design of mobile phones enables the user to have the biggest freedom of movement. The area
of mobile phone service divides into many memory cells in the form of hexagonal honey-comb
(called Cellular Network). There is an antenna in each cell, which is connected to the respective
exchange station that process mobile telephone calls through cables. The mobile phone uses the
connection of radio signal and antenna to achieve the highest mobility for telephone
communication.
When making a call, the exchange station that responsible for processing the mobile phone calls
would group it according to its nature. If it is necessary to connect with fixed network telephones,
the signal will be transmitted to general exchange stations. If the call needs to be connected with
another mobile phone, the computer will choose the closest antennae. Followed by phone calls
roaming all over the world, the exchange station would determine the time of changing the
service memory cells according to the strength of the radio signal automatically. The telephone
conversation certainly would not be interrupted or terminated due to the switching movement in
the entire process.
Why does telephone develop rapidly?
After the invention of telephone, it has been recognised as the best communication tool for
people in the future. The patent right owner Bell then started to develop it with his partners with
great efforts. They changed their work focus from developing telephones to improving and
promoting their invention. After 100 years, Bell Company (renamed as AT&T) has developed as
the biggest company of the world, which was even more established than the government
organisations of some nations. Before the restriction made by the US Congress to the AT&T
Empire in 1984, it has employed more than a million staff and had more than 100 millions of
telephones.
During the Second World War, the US Government has invested a huge amount of resources at
telecommunication development for winning the battle and for military contest. This
phenomenon still exists among different countries to date. With its support, telephone
communication technology improves continually. For examples, the Global Positioning System
(GPS) was invested and controlled by the US Department of Defence in early time, but it has
been popularised to apply in daily life in the recent years.
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Students’ version
Extended reading:
Mobile telephone system development
It has been quite awhile since the dawn of mobile phones, and the history of mobile phones can
be categorized into three different stages: analog communication systems, digital communication
systems, and third generation mobile phone systems. Also, how do mobile phone systems
transmit signals? To understand signal transmission, we have to investigate the so-called
hexagonal networking structure first.
Hexagon networking structure
Hexagon networking structure is composed of many broadcasting sites, and every one of the
broadcasting sites manages the local area's wireless communication. The broadcasting sites have
a tower that relates and connects information with neighboring areas, and that is how a wireless
telecommunication web is formed. Since every tower has their own respective area of coverage,
the map of the network of areas resembles the image of a hornet's nest, and that's where the name
hexagon networking structure comes from.
In addition, how is the location of these broadcasting sites determined? Because of the fact that
each broadcasting site can only process a limited amount of signal information, areas with higher
population such as Mongkok, Central, Causeway Bay have higher usage rates and therefore
higher concentration of broadcasting sites to process the large volume of wireless
telecommunication. As for the less populated areas such as countryside (Lamma Island, Shek O,
Kam Tin) and New Territories (Tin Shui Wai, Sheung Shui, Tsing Yi), the usage rates are
relatively lower and therefore have less concentration of broadcasting sites. Thus, the mobile
phone accounts that are located in more remote areas will often experience less signal receipt
than the more populated areas, or sometimes even no signal at all, and this is all due to the lack of
broadcasting sites.
Signal Processing Mode
Signal processing mode refers to process that occurs when signal is transferred from one mobile
phone account to another. First let us introduce the process of signal processing. When two
different mobile phones are connected with each other, the phone will turn the user's voice into a
wireless electronic signal, and then from the broadcasting site's tower, it is distributed as a form
of electronic waves. These processed signals will then be picked up from neighboring
broadcasting sites and relayed to the other mobile phone and transformed back into the user's
original voice. If two users are in between great distance that spans numerous broadcasting sites,
then the electronic waves will travel through the web of broadcasting site network, from one site
to another. Utilizing the web network structure, signals can be sent to many different locations.
After a basic understanding of signal processing, let us go deeper and discuss the two different
modes of signal processing.
Analog Signal Processing
The first generation of mobile phones used analog signal processing, and in the process of analog
signal processing, the signal take on the form of waves, which is different than that of the digital
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Students’ version
signal processing discussed below. In the process of signal processing, signals are first
transformed into electronic waves and then sent out. Due to interference with other electronic
waves during traveling, the signal that is received at the destination will be somewhat reduced.
Analog technology shapes the interfered signals back to its original form. Since the level of
interference varies with the different areas, so the shape of the signal will never be exactly the
same as its original.
Digital Signal Processing
Digital signal processing is branded as the second generation of mobile phones. Compared to
analog signal processing, they are similar in that they both use electronic waves to transmit
signals, and differ in that digital processing uses only numbers 1 and 0 to represent the shape of
the electronic waves. In this process, signals also encounter interference, but since the electronic
waves are binary and can only take on two forms, the reduction in the signal will be much less
and the signal will be shaped back to exactly the same as its original.
GSM System
GSM system uses the prior mentioned hexagon networking structure along with a technology
called channel reusability. Channel reusability refers to the idea of repeatedly using the channel
by first splitting one channel into many narrower frequencies, and then using them as pieces of a
puzzle and spread them onto the different areas. This is the underlying concept of channel
reusability. Using this technology, we can reuse one channel, thus avoiding a lot of channel
establishment as well as labor and resources.
CDMA System
The difference between CDMA system and GSM system is in the frequency looping technology.
CDMA system not only uses both hexagon networking structure and channel reusability, it also
uses frequency looping technology, which is using every available frequency in the vicinity of
the area. However, everyone might wonder about the heavy interference that might come with
using this system, but in reality, there are no such interference issues. Then what exactly is this
frequency looping technology that the CDMA system uses? When CDMA users receive signal,
the frequency in use will loop with time in attempt to reduce the probability of other users using
the same frequency during the same time interval. If there are more than one user receiving the
signal, then the frequency that they are using will loop as well and, in addition, be randomly, thus
reducing the interference, and this is the marvel of frequency looping.
Error Correcting Code
During the process of signal transfer, some interference and errors are bound to occur, and
mobile phone systems have a method to correct such errors. To avoid mistakes in information,
signals are transferred repeatedly for multiple times. When a interference occurs during the
process of transfer, mobile phone systems can correct the signals received. Below are two
methods of such Error Correcting Code.
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Students’ version
The actual method is pretty simple. If the system was to transfer a "1", this signal during transfer
process will repeatedly transfer for multiple times such as five times. Because of interference, the
signal received will have an error such as receiving a "0" instead of the "1" that was transferred.
When the system discovers that the signal does not follow the repeated "1" pattern, it will
recognize the mistake and make the correction, by using the majority as the correct signal. As the
figure shows, when the signal transfer shows the amount of "1" is the majority when compared to
"0", then the "0" will be corrected. Using this method, the system can correct signal errors such as
the other example shown in the figure. Through this Error Correcting Code, the errors will be
corrected.
(Error Correcting Code)
Source: <EDB Wireless telecommunication>
http://resources.edb.gov.hk/physics/articleIE/telecom/telecom_e.htm
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Students’ version
Lesson 5, 6: What are the modern telephone
communication development
techniques?
Background
The application of radio wave should be the most conspicuous revolution of
telecommunication techniques recently. Its application extends from developing indoor wireless
telephone and later mobile phones. In Hong Kong and other places around the world, there are
millions of people using mobile phones. Do you have your own mobile phone? Mobile phones
make use of extremely tiny components that combines the handset of traditional telephones and
the base part into one body. It is not necessary to be connected with the network by cables and
allows wide areas of movement than indoor mobile phones. In addition to general phone services,
the new generation mobile phone supplies wireless Internet connection to allow users to send
e-mails and browse websites by the mobile phone. Other services included video conferencing
and Global Positioning System service (GPS), etc.
Activity 4: Demonstration of the modern technology
1. Voice-over IP (VoIP)
VoIP is the conversational service of carrying packages of voice signals over the IP network.
Assisting with technological improvement in different areas and researches on exploring
various applicable domains, it is becoming more popular in application.
Basic technology of VoIP: Commonly used exchange devices of telephones do not have the
process to package voice signals. The transmission of sound occurs during each timeslot of
the conversation in both sides. Conversely, VoIP would package multiple conversations after
redirecting it into a common communication access. Usually, this access is not only used for
processing voice, but also shared by other information. As a result, the delay of sound and
system stability are the biggest problem of VoIP. If the transfer rate of the network is slow or
there is other information transfer at the same time, the efficiency of VoIP would be affected.
Since the VoIP technology could achieve higher capacity by the use of more powerful CPU
and faster network transmission speed, its quality is almost comparable with conventional
telephones. At some specific locations, it may even achieve at the same high quality as
general telephones.
The teacher would demonstrate the operation of the new technology now.
Materials:
VoIP connector, computer, microphone, loudspeaker
Application:
Register at the website of Free World Dialup (FWD) http://www.freeworldialup.com and
adjust to the appropriate frequency to use the service
Question: What are the advantages of VoIP?
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2.
Third generation (3G) mobile phone system
3G（Third Generation）is the abbreviation of the third generation mobile
phone system. It makes use of a newly developed telecommunication
technology to allow the users of mobile network to enjoy a high-speed
network service. We can surf on the internet, enjoy the information of
leisure and entertainment and to enquire information about different
professional services at the any time. It is different from just limited by
television and personal computers for accessing network services.
Commercially, the electronic trading activity would be more widespreading such as store
and retrieve information from the internet by mobile phones and holding video conferences,
etc. Through 3G technology, the speed of access controls of each user can be accelerated to
2M bits/s, which is faster than the transferring speed of GSM system for 40 times. The data
processing capacity of the system also increased a lot and allowed the system to support
high quality video transmission services. That is why 3G technology is more advanced than
the traditional technology.
What do 3G technology bring to us in general? The characteristics of 3G technology are
characterized by the mobile phones as the-state-of-the-art, easy to control and has a
humanized interface. It can supply instant multimedia communication and the GPS roaming
functions. Moreover, users can access the internet at a high speed and send e-mails. 3G
technology has introduced to Hong Kong now, and we can enjoy those novel services
through the 3G mobile phone system.
The teacher would demonstrate the operation of the new technology now.
Materials:
2 or more 3G mobile phones, demonstrate video telephone, video conference, instant
information transfer and multimedia information reception and dispatching.
Question: What are the advantages of 3G when compared with the conventional mobile
phones?
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＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿＿
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3.
GPS (global positioning system)
The entire GPS system consists of three parts, the control part, the satellite part and the
receptor. For the control, there are a main control station and a few monitoring stations for
tracing the exact position of the satellites. They trace the position of the satellite, check the
operations and send commands to the satellites to ensure they operate properly. The satellite
part is composed of 24 satellites, which travel around the earth in every 12 hours on 6
trajectories. It continual emits orientating signals from 26560 km from the sky to the land.
The receptor parts are the users themselves that can calculate the exact position accurately at
any weather and landscape by the signals emitted from GPS satellites.
GPS was controlled by the US Department of Defence at the early time, but it has become
more popular for using in daily life recently. Many advanced countries are developing in the
direction of constructing digital maps so that people can be aware of their own location and
the surrounding environment through this kind of map. Nowadays, GPS has become widely
used, particularly in navigating planes, ships and cars, etc. as well as applied in phones.
Materials:
Use PDA or equipments having the function of GPS to demonstrate your present location.
Question: What kinds of practical uses does GPS provide?
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Conclusion:
The course of telephone development and the development of telecommunication
technology has been over 100 years, and they are the fruitful results by the continual efforts of
the scientists and researchers. Through the process of telecommunication technology
development, we can understand that the popularised development of individual achievement
needs the supports from various organisations, institutions and governments during the
process of science and technology development. In the same time while science and technology
continuously make progress to and improve our living, we should also notice the appropriate
ways to apply science and technology, which would be beneficial to people and we should
prevent them from being abused causing all possible dangers.
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Students’ version
Additional background information:
Blue Tooth Technology
Blue Tooth products can conduct wireless communication in a short distance. The origin of the
name Blue Tooth came from a tenth century Norway king. This king ruled Denmark, and if you
translate his name to English, it becomes ¡§Blue Tooth¡¨. This technology was named after him
in hopes of the technology will one day become the standard throughout the world.
In the earliest stages of wired-network, every component is connected by a wire that provides the
information transfer, which greatly reduced the flexibility and reach of communication. In the
recent years, Infrared (IR) communication's implementation removed the inconvenience of wires,
but had a big drawback of relying on the position of the IR sensor to provide communication,
similar to a television remote. The user has to be in short distance of the device's sensors and in
range of its line of sight for it to control it properly. When Blue Tooth products are introduced, it
will solve the problems mentioned above; allowing communication in a distance of up to ten
meters and are not restricted to direction and wires. Currently on the market, there have already
been some manufacturers who introduced electronic products that contain Blue Tooth technology,
such as the recently popular wireless headphones. The headphones are popular with users
because it does not need a cable to achieve its purpose, and with the support of other Blue Tooth
products such as noting a destination phone number on a hand-computer, the Blue Tooth wireless
headphones will automatically dial the number fast and conveniently.
Internet
Since the emergence of the Internet in the 90's, it has been developed so fast and we cannot live
without it already. As a result of the technological development, the information transfer rate also
increased from tens of thousands of bytes per second to millions bytes per second. Since then the
transmission of sound and visual image become possible and it is also convenient to use.
Therefore the Internet telecommunication service has already become more and more
popularised.
Optical fiber
The core of simple optical fibres is made of medium with a larger refractive index with the outer
layer made of medium of lower refractive index, which forms a tiny filament. The raw material
of the medium is usually glass or plastics. When shooting light to one of the end of the fibre, the
light will be transmitted in it. Total internal reflection will occur when it reached the boundary of
centre and outer media, the light beam is directed back to the core. Although the light travels in
straight line, it would be transmitted through the direction of optical fibre even though when it is
bended. The optical fibre has broad applications in addition to communication. It can also be used
for making medical equipments such as endoscopes, inductors or for decoration.
Modern optical communication makes use of the strength of light beams to denote different
information. By shooting light beams carrying information at one end of the optical fibre, the
optical fibre would then can direct the light beam and transmit it to the receiver at the other end.
When there is converter to resemble the light signal, the original information can be acquired. As
the loss of light is little in glass fibre, it is not necessary to have transition stations and the
information can be transmitted through a very long distance. As an optical fibre with thickness of
several microns (thinner than hair) is capable for transmitting more than tens of millions of
impulses already, it is more superior than copper wire communication . It could gradually replace
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Students’ version
it as the major communication medium.
Communications satellite
Satellite communication refers to the use of artificial satellite as the transition station to transmit
radio signals through two or more communication stations. Satellite communication makes use of
earth stations to transmit the wanted information signals in the form high frequency radio waves
to satellites in the space, and then the signals are transmitted from the satellites down to the
satellite signal receiving stations. A uni-directional or bi-directional communication satellite
system is established from it.
Source: <EMB Wireless telecommunication>
http://resources.emb.gov.hk/physics/articleIE/telecom/telecom_e.htm
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