1. EE 3131 EE 3801 Telecommunications Fundamentals
Wei Jin Alan Pak Tao Lau
Professor Assistant Professor
CF CF608
Tel: Tel:
Department of Electrical Engineering

2. Assessment Methods Coursework: 40% Assignments (5%):
Questions and exercise problems at the end of each chapter
Midterm Tests (30%)
Lab. (5%):
One lab report chosen from any of the three experiments needs to be handed in one week before the exam.
Examination: 60%
The duration will be 3 hours. All questions will be compulsory.
Course notes: ftp.ee.polyu.edu.hk/aptlau/telecom

3. Laboratory Experiments
The experiments will be performed in the Control and Signal
Processing Laboratory in EF401.
Three experiments need to be done. The experiments will be on:
(1) Conventional Amplitude Modulation (Envelope Modulation)
(2) Time Division Multiplexing
(3) Pulse Code Modulation
You will be informed of the schedule of the labs in due course.

4. About the Instructor Alan P.T. Lau Office hours: Wed 10-12 am
B.A.Sc. (2003), M.A.Sc.(2004), Electrical and Computer Engineering, University of Toronto, Canada
Ph.D.(2008), Electrical Engineering, Stanford University, USA
Research area: Fiber-optic communication systems
Wireless communication systems
Office hours: Wed am

5. Potential problems I foresee on my side:
Some course logistics
Potential problems I foresee on my side:
Lecture planning
Assumption of Background
Speed of instruction
Background assumed:
AMA 201, 202 or 203: linear algebra, matrix, eigenvalue, eigenvector, Laplace transform, Fourier transform

6. Some expectations For myself From you
Prepare for lecture, on time, free to talk after class
From you
Turn your mobile to silent and don’t disturb others
Most importantly, participate ~

7. Course Outline Main Chapters: Introduction to Telecommunications
Signal and Systems Analysis
Amplitude Modulation (AM)
Angle Modulation
Pulse Modulation
Digital Communications
Optical Fiber Communications

8. Introduction to Telecommunications

9. Introduction to Telecommunications
Objectives:
To provide a broad overview of communication systems
To describe the main components of a communication system
To introduce the concept of a signal
To classify different types of communication systems
To introduce the concept of modulation in communications
To introduce the effect of noises in system performance
To describe the key factors to evaluate the performance of a
communication system

10. Introduction to Telecommunications
What does telecommunications mean?
Telecommunications consists of “tele” and “communications”.
“tele” “over a distance”
“communications” “the process of exchanging information”
Thus , telecommunication means exchanging information over a distance.
What are some communication systems we used everyday

11. Typical Communication Systems
Copper wire communication:
Telephone
Modem, DSL, Broadband
Wireless Communication:
Cellular communication
Radio, TV Broadcast,
Satellite communication
Fiber-Optic Communication
Global Long-Haul communication

12. The importance of communication systems in modern lives
Applications resulting from the development of comm. technologies
Yahoo (1994), (1996), ICQ (1996), Google (1998),
MSN(2000), Friendster (2001), Facebook (2004), Youtube (2005)
HDTV (2008), cell phone with data transfer (GPRS) (2000), Wi-Fi (2001), video phone (2005)
Now, you can:
Buy things online
Do transactions online and through your cell phone (e-banking)
SMS, message people instantly (ICQ,MSN)
Do almost anything ... Even break up with bf/gf online~~~

13. Components of a communication system
Cell phone system
Person who talks on a phone (message source) 
Micro-phone (sound is converted into electrical signal)
Sender antenna to base station to receiver antenna (transmission channel)
Speaker (electrical signal is converted back into sound)
Person who listens (message destination)

14. Components of a communication system
Cable TV Broadcast system
Images or actions to be filmed (message source) 
Video camera (image message is converted into electrical signal)
Underground cables (transmission channel)
Television at home (electrical signal is received and converted back into image message)
Person who watches television (message destination)

15. Components of a communication system
Block diagram of a communication system:
Source
Transducer
Transmitter
Channel
Destination
Receiver
message
Input signal
Transmitted signal
Received signal
Noise, distortion
Output signal
Output message
Channel
a medium for signal transmission (e.g. copper wire, optical fiber, or free space). Introduce noises and distortion.
Receiver
to recover (demodulate) the output signal from the channel.
Output transducer
to convert the message signal back into the original message. (e.g. speaker, TV)
Destination
the unit to which the message is communicated.
Source
generate a message (human voice, TV picture, or data)
Input transducer
convert a message into a signal (message signal). e.g. microphone, video camera, etc.
Transmitter
to modify (modulate) the message signal for transmission into channel.

16. Classification of communication systems
Depending on the transmission media (channel) used:
line communication system
In line communication, transmission is carried out on the transmission line.
e.g. wire, coaxial cable, optical fiber, etc.
wireless communication system.
In wireless communication, signals from various sources are transmitted through a common media – open space.
e.g. radio, microwave, etc.

17. Classification of communication systems
According to the characteristics of transmitted signals, we have
analog communication system and digital communication system.
At present, only AM,FM radio remain to be analog communication systems.

18. Classification of communication systems
Duplex (2-way) communication
Phone Conversation
Internet
Simplex (1-way) communication

19. Signals in communication systems
Source
Transducer
Transmitter
Channel
Destination
Receiver
message
Input signal
Transmitted signal
Received signal
Noise, distortion
Output signal
Output message
Focus of this course
In a communication system, a message must be converted into a signal before it can be transmitted in the transmission channel.
What is a signal?

20. Telecommunications
A signal is a set of information or data and is usually a function of time. A typical example of a signal is a time varying electric current that contains the message.
An example of time domain signal waveform
Should we just simply send a signal from a phone directly to the channel?

21. Modulation for transmission
In a communication system, the function of transmitter is to modify the message signal for efficient transmission to the channel, that is, to perform modulation.
What is modulation?

22. Carrier Wave and Modulation
What is a carrier wave?
In communications, a carrier wave is a sinusoidal wave of high frequency. For example,
Carrier Frequency
Phase
amplitude
Modulation is the process of impressing information onto the carrier for transmission by varying a parameter of the carrier in proportion to a signal. This parameter may be the amplitude, the frequency or the phase of the carrier wave. For example, given a signal m(t), amplitude modulation (AM) can be achieved by multiplying m(t) with the carrier:
m(t) – original signal (baseband signal)
g(t) -- modulated signal (bandpass signal)

23. Carrier Wave and Modulation
Modulation is performed by the use of a modulator.
A modulator is a product device, it varies the carrier wave in accordance with the message signal and the resulting modulated signal “carries” the message information.
It carries no information
It carries m(t)

24. Bandwidth of a signal
Bandwidth is the portion of electromagnetic spectrum occupied by a signal.
Example:
A signal frequency range is
902 to 928 MHz. What is the
signal bandwidth?
f1 = 902 MHz, f2 = 928 MHz,
then
BW = f2 – f1 = 26 MHz
902
928
If a signal has too large of a bandwidth for the channel, it will undergo distortion (explain) and affect system performance

25. Why is modulation necessary?
Why not just transmit the signal directly?
Several reasons:
1. Efficient transmission:
By the use of modulation, message can be transmitted at a desired frequency band.
For example, in radio waves transmission, then for efficient radiation of electromagnetic energy, the physical dimension of the radiating antenna should be at least  0.1.
Frequency range of a speech signal: 100 to 3000 Hz
Since f = c  100 km    3000 km.
An impracticably large antenna!!!

26. Why is modulation necessary?
2. Frequency allocation and efficient spectrum utlilzation:
Modulation can shift the frequency spectrum of the signal to the location centered on the carrier frequency.
e.g. different radio broadcast station has different carrier frequency and modulation allows you to choose the one you like. =
Modulation moves signal spectrum to its assigned frequency range without
overlapping and thus realizing Frequency Division Multiplexing (FDM).
We will talk more about it on Chapter 3

27. Frequency Spectrum Allocation for HK Radio

28. Noise in communication systems
What is noise?
undesired signal which carries no information
random and unpredictable, produced by the natural processes

29. Noise in communication systems
If the noise level becomes high, the information cannot be recovered
Even for lower noise levels, the quality of the information reception will be reduced. (think of bad cell phone reception)

30. Noise in communication systems
In a communication system, there are two main types of noises:
The electrical noise that is introduced in the transmitting medium is termed external noise.
The noise introduced by the components in
the transmitter and receiver is known as internal noise.

31. Noise in communication systems
External Noise
External noise includes two main types:
Man-made noise:
produced by electromagnetic waves generated by things like electric motors, power lines, etc.
Atmospheric noise:
caused by naturally occurring disturbances in the earth’s atmosphere due to, e.g. lightning, etc.

32. Noise in communication systems
Internal Noise
Internal noise is produced by electronic circuits.
There are two types of internal noise:
thermal noise and shot noise.

33. Noise in communication systems
Thermal Noise
Thermal noise is generated in a resistive component due to the rapid and random motion of electrons and atoms inside the component.
This motion increases with increasing temperature (hence, “thermal”).
This random motion of electrons produces an unpredictable component in a current passing through a resistor (hence, “noise”).
It is sometimes referred to as Johnson noise, after its discoverer.

34. Noise in communication systems
Shot Noise
Shot noise exists in all active devices, especially in transistors.
It is caused by random variations in the arrival rate of electrons or holes at the output of the device.

35. Shot noise and thermal noise are additive.
Noise modeling
Shot noise and thermal noise are additive.
Noise is one of the factors that limit communication system performance
 it needs to be measured.
How to measure the amount of noise?
Noise

36. Signal-to-Noise Ratio
Signal-to-Noise Ratio (SNR or S/N) provides a comparison of noise and signal powers at the same point. It is defined as
and in decibel form (which is usually convenient) as

37. Limits of communication systems
Noise imposes a limit on the rate of information transmission Noise is unavoidable.
Why is noise unavoidable?
At any temperature above absolute zero, thermal energy causes microscopic particles to exhibit random motion. The random motion of charged particles such as electrons generates random currents or voltages called thermal noise.
Thermal noise exists in every communication system.

38. Limits of communication systems
Due to various reasons, every communication system supports transmission at certain limited frequency bands only.
Bandwidth and noise limit the communication system performance.
Usable Bandwidth

39. Communication System Performance
How to evaluate the performance of a communication system?
1. Efficiency -- To determine the capacity of transmission channel per given bandwidth;
2. Reliability -- To determine the signal quality.
In an analog communication system,
Efficiency is measured by transmission channel bandwidth, B.
Reliability is measured by system output signal-to-noise ratio (S/N).

40. Communication System Performance
Example
A conventional amplitude modulation telephone system requires 8 kHz bandwidth while a new modulation format requires 4 kHz bandwidth . Therefore,
the new system has a higher efficiency than the conventional system.
A telephone system requires a S/N at least 20 dB and a TV picture needs its S/N above 40 dB.

41. Communication System Performance
In a digital communication system, efficiency is measured by bit rate, R, and reliability is measured by bit error rate, Pb.
Bit rate: R = n/T (bits/sec)
where n is the number of bits sent in T seconds
Bit error rate:
Pb = number of error bits / total number of bits sent
e.g. a digital telephone system requires Pb < 10-3  10-6
and data communication requires Pb < 10-9.

42. Summary

43. Questions: Draw a block diagram of a basic communication system.
What is a transducer? What is a signal? What is carrier?
What are main types of internal noise?
Why is modulation important in a communication system?
How to evaluate a communication system?
What are the factors limiting the performance of a communication system?
Find the SNR in dB if the ratio of signal power to noise power is:(a)10 ?(b) 100 ?
Assuming constant noise power, if signal power is increased by 3dB, by what factor is the SNR increased?

44. Trig. identities Calculus Taylor series Probability
Some math revisions:
Trig. identities
Calculus
Taylor series
Probability

45. Questions
1. Can you increase the SNR by amplifying the signal before the receiver? Why or why not?
2. What type of noise does a transistor has?
3. Find the SNR in dB if the ratio of signal power to noise power is:(a) 10 ?(b) 100 ?

46. Components of a communication system
Cell Phone system
Cable TV Broadcast system
Source
Speaker
TV Station Crew
Transducer
Microphone
Video Camera
Channel
Wireless
Copper wire/Fiber TV
Destination
Listener
Viewers

47. Telecommunications

48. Telecommunications
Modulation can be performed by multiplying the message signal, m(t), by a carrier wave (sinusoidal signal), cosct.
e.g.
g(t) = m(t) cos(ct)
where m(t) is the message signal (baseband signal, modulating signal -- signal before modulation), cos(ct) is the carrier wave, and
g(t) is the modulated signal (bandpass signal, signal after modulation).

49. Telecommunications
Notice that after modulation
the signal transmission takes place at the high frequency carrier which has been modified to carry the lower-frequency message signal.
How to perform modulation?

50. Telecommunications 3. Efficient spectrum utilization:
The channel bandwidth may be much larger than the signal bandwidth. It would be wasteful if only one signal is transmitted over the channel.
Modulation moves signal spectrum to its assigned frequency range without overlapping and thus realizing Frequency Division Multiplexing (FDM).
Multiplexing is the process of combining several signals for simultaneous transmission on one channel.

51. Telecommunications
When a signal changes rapidly with time, its frequency is high or its spectrum extends over a wide range and hence the signal has a large bandwidth.
Similarly, the ability of a system to follow signal variation is reflected in its frequency response or transmission bandwidth.
A rapid signal variation  a large signal bandwidth
 a large transmission system bandwidth
What is the consequence of insufficient transmission bandwidth?
severe distortion.

52. Telecommunications
Thermal Noise
Its frequency content is spread uniformly throughout the usable spectrum, hence it is also known as white noise.