Communication systems design for the CM.pptx

EE 401
Communication Systems
Lecture #1

Lecture Overview
 The objectives of today’s lecture are
 Explain the course mechanics
 Provide an overview of the course
 Describe the major components of the
course

Required Course Materials
 Textbook:
 B.P. Lathi, Modern Digital and Analog
Communication Systems, 4th Ed.
 References:
 Slides will be posted online on Google
classroom
 Live Zoom sessions
 Some videos

Course Components
 The course has two main components:
 Lectures – These are meant to introduce the key
concepts in the course and provide you with
fundamental understanding. This is the primary
source of information in the class. I will provide
you with lecture notes on the website typically
the weekend before class. Attending the lectures
is absolutely crucial to successfully completing
this course!
 Exams – These are meant to show me how well
you have grasped the material .

Grading
 Quizzes
 Assignments
 CP
 Mid Exam
 Final Exam
20%
5%
5%
30%
40%

Course Objectives
 After successfully completing this course
the student should
 have information about the
communications, types of
communication systems,
 be able to explain the operation of the
system components, modulation,
multiplexing, analog and digital
communications, satellite communicaitons

What is Communication?
 Definition: Communication is the
transfer of information at one time or
location to another time or location.
 Generic Communication System:
Channel
Receiver
Transmitter
Received
signal
Transmitted
signal
Communication System
Estimate
of message
signal
User of
information
Source of
information Message
signal

Fundamental Steps in
Communication
1. Generation of message signal: image,
voice, music, video
2. Description of the message signal by a set
of symbols : electrical, aural, visual
3. Encoding of the symbols in a form suitable
for transmission
4. Transmission of the encoded symbols to
the desired destination
5. Decoding and reproduction of the original
symbols
6. Recreation of the original signal

Primary Communication Resources
 Transmitted power
 The average power of the transmitted
signal
 Channel bandwidth
 The band of frequencies allocated for the
transmission of the message signal
 band-limited channels
 Telephone systems: 300-3100 Hz
 Power-limited channels
 Satellite channel

A Communication System
 Source of Information
 Information may take many forms: computer
data, image, voice, music, video.
 Information can be either analog or digital.
 Analog information can also be
‘digitized’.
 Information is defined as the amount of
“surprise” at the rx (reciever).
 Transmitter
 Processes information and puts it into a form
suitable for transmission
 This typically means transforming into an
electromagnetic signal
 Can be either ‘baseband’ or ‘bandpass’

A Communication System (Contd.)
 Channel
 Relays information between locations (without
perfect fidelity)
 Guided propagation and free propagation are
possible.
 telephone channels, coaxial cables, optical
fibres
 Wireless broadcast channels, mobile radio
channels, satellite channels.
 Receiver
 Must reconstruct transmitted information from
the corrupted/received waveform as accurately
as possible

Communication System (Detailed)
 Transducer
 Converts the input signal to electrical waveform (baseband
signal) and vice versa

Communication Systems (Contd.)

A Communication System (Contd.)
 Modulation
 Modification of the
message signal by the
transmitter in a form
suitable for transmission.
 Demodulation
 Recreation of the
message signal from
received signal (a
degraded version of the
transmitted signal)
Modulated
signal
Message
signal
Carrier

Modulation
 Continuous-wave (CW) modulation
 A sinusoidal wave is used as the carrier
 Amplitude modulation (AM)
 Frequency modulation (FM)
 Phase modulation (PM)
 Pulse modulation
 Carrier consists of periodic sequence of rectangular
pulses
 Analog pulse modulation
 Pulse-amplitude modulation (PAM)
 Pulse-duration modulation (PDM)
 Pulse-position modulatiob (PPM)
 Digital pulse modulation
 Pulse-code modulation (PCM)

Bandpass vs. Baseband
 The information signal or message signal m(t) is a
baseband signal, that is it contains energy about D.C.
(f = 0)
 The transmitted signal may be at baseband or may be
a bandpass signal, that is it contains energy about f
= fc where fc >> 0.
 Wireless signals are (almost) always bandpass due to
physical antenna limitations whereas wireline signals
could be either bandpass or baseband .
 Each wireless application is assigned a specific
frequency band in which it can radiate energy. This is
one reason why Fourier Transforms (spectral
information) are so important in communications.

Examples of Communication Systems
 Broadcast Radio
 Music and voice are transmitted from a broadcast station to
large number of receivers (i.e., radios) over the air
 Broadcast Television
 Images are transmitted from a broadcast station to a large
number of receivers (i.e., TVs) over the air
 Telephone system
 Voice (digital data also possible) transmitted from one point to
another point (i.e., one phone to another) through wires
(both copper and optical fiber)
 Cellular telephone
 Voice (digital data also possible) transmitted from one point to
another point through both wires and over the air
 Internet (computer networks)
 Digital data transmitted from one point to another point
through wires
 Satellite communication systems
 Digital data or voice transmitted from one point to another
point using satellite as an intermediate transmitter/receiver

What Makes a Good
Communication System
 Good Received Signal Fidelity
 Analog System: high Signal-to-Noise Ratio
(SNR)
 Digital System: low Bit Error Rate (BER)
 Low Transmit Signal Power
 A large amount of information is
transmitted
 Signal occupies a small
bandwidth
 System has a low cost
(complexity?)
 Complex digital operations have steadily
grown cheaper
 Communications engineers must trade off
all of these

Examples of Tradeoffs in
Communications
Designs
 Satellite and Deep Space Communications
 Power is expensive to generate in space and
transmission distances are enormous – Must be
very energy efficient
 Microwave Relay Towers
 Power is cheap, but available bandwidth is
restricted by regulation - Must be very
bandwidth efficient
 Cellular Phones
 Power is costly (impacts battery life and size)
but bandwidth is also limited - Must be both
bandwidth and power efficient

Digital vs. Analog Communications
 Digital Communication System
 transmit a finite number of signals
 text & data are naturally digital information
sources
 Digital signal are more robust to noise.
 Analog Communication
 transmit a continuous (uncountably infinite)
range of signals
 voice and video are natural analog information
 An analog information source can be
converted into a digital source by
 Sampling the signal in time
 Quantizing the signal amplitude to a finite
number of levels

Analog to Digital Conversion (A/D)
 An analog signal is converted to a digital signal by
means of an analog to digital (A/D) converter
 The signal m(t) is first sampled in the time domain.The
amplitude of the signal samples ms(kT) is partitioned
into a finite number of intervals (quantization)
 The sampling theorem states that if the highest
frequency in the signal spectrum is B, the signal can be
reconstructed from its samples taken at a rate not less
than 2B sample per second

Key Inventions in the History
 1844 Telegraph (Morse)
 Morce code of variable-length ternary
code
 1864 Maxwell’s equations (Maxwell)
 Formulation of the electromagnetic
wave propagation
 1875 telegraph code of fixed-length
(Baudot)

 Words consists of 5 equal length code
elements
Elements are assigned to two possible
states: a mark or a space (0 or 1 in
difital systems)
 1875 Telephone (Bell)
 Real-time transmission of speech by
electrical encoding and replication
of sound
 1894 Wireless Communication
(Lodge)
 Short distance (150 yards)
 1897 Automatic Switch (Strowger)
 Electromechanical switch
 1901 Wireless Communication
(Marconi)
 1700 miles over Atlantic
ocean
 1918 Practical AM receiver
(Armstrong)
 Superheterodyne radio
receiver
 1920 First Radio
Broadcasts
 1928 Television (Farnsworth)
 1928 Nyquist criteria (Nyquist)
 1933 FM Radio (Armstrong)
 1936 BBC begins first TV broadcasts
 1937 Pulse-code Modulation (Reeves)
 1948 Information Theory (Shannon)
 1948 Transistor (Brattain, Bardeen,
Shockley)
 Electronic switching and digital
communications
 1950 Digital Long Distance Telephone
Lines (Bell Labs)
 1962 Telstar I communication satellite
(Bell Labs)
 1979 First commercial cellular
telephone (Motorola/AT&T)
 1990 Second Generation (Digital)
cellular systems (TDMA)
 1993 CDMA Cellular systems
 2002 - Third Generation
 Cellular Systems

EE 401
Communication Systems
Lecture # 4
Fourier Integral
Fourier Transform

Overview
The Objectives of Today’s Lecture
• To introduce Fourier integral, Fourier transformation
• To present transforms of some useful functions
• To discuss some properties of the Fourier transform

Aperiodic Signal Representation

Fourier representation of gT0(t)

Computing the limT0 ∞
→ of gT0(t)

Fourier & Inverse Fourier Transform

Communication systems design for the CM.pptx

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