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Session 2013Lecture # 2
InstructorKashif Shahzad
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Course Details Text Book: Electronic Communication System by
Kennedy and Davis
Reference Text: Modern Digital and Analog Communication System by B.P. Lathi
(Soft copy is available on group page)
Course Instructor: Kashif Shahzad Email: [email protected] Cell: +92 333 5186231
Course homepage: http://groups.yahoo.com/group/prestonadvcommsystems
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Course Breakdown
Assignments: 10%Quizzes: 10%Others: 05%Mid Term: 25%Terminal: 50%
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Learning Objective Explain the principles of a communication
systems Discuss the nature of information, different types
of signals involved and their characteristics Make the distinction between Analog and Digital
communication systems Determine the need of modulation and
differentiate various type of modulation techniques in time, frequency domain
Important steps in analog to digital conversion, PCM, PAM, PPM etc
“We will deal with almost every important phenomenon at physical layer level”
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Review of last week (Lecture 1) Basic concept of Data, Information and Redundancy
Relationship of Data and Signals
Signals and Systems
Different types of Signals (Chp 2 Reference) Analog vs Digital Continuous vs Discrete Periodic vs Aperiodic Energy vs Power Stochastic vs Deterministic
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Today’s MenuEssential Parts of Communication System
TransmitterReceiverChannel
Time and frequency domain relationshipConcept of Spectrum & BandwidthConcept of Passband & Baseband SignalsModulation & DemodulationFourier Series (3 types)
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COMMUNICATION OVER LONG DISTANCES IS NO LONGER A PROBLEM.
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Communication : To transfer information from one place to another
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Communication System History 1837 – Samuel Morse invented telegraph. 1858 – First telegraph cable across Atlantic (Canada –
Ireland) 1876 – Alexander Graham Bell invented telephone. 1988 – Heinrich Hertz introduce electromagnetic field theory. 1897 – Marconi invented wireless telegraph. 1906 – Radio communication system was invented. 1923 – Television was invented. 1938 – Radar and microwave system was invented for World
War II. 1950 – TDM was invented. 1956 – First telephone cable was installed across Atlantic. 1960 – Laser was invented 1962 – Satellite communication 1969 – Internet DARPA 1970 – Corning Glass invented optical fiber. 1975 – Digital telephone was introduced. 1985 – Facsimile machine. 1988 – Installation of fiber optic cable across Pacific and
Atlantic. 1990 – World Wide Web and Digital Communication. 1998 – Digital Television. 9
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The Real AimThe Real Aim“If the information that you want to send is your voice, how to make sure that what you are saying is understood by your friend?”
Basic Parts of a Communication System
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Basic Communication System
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Transmitter Transmission Medium Receiver
InputTransducer
Output Transducer
Noise
wired / wirelessmtx(t)
s(t) r(t)
ptx(t)
n(t)
mrx(t)prx(t)
s(t) – Input signal; audio, video, image, data etc.mtx(t) – Modulating signal; input signal that has been converted to electrical
signal.ptx(t) – Modulated signal transmit by the transmitter.n(t) – Noise signal.prx(t) – Modulated signal receive by the receiver.mrx(t) – Modulating signal at the receiver.r(t) – Output signal.
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Component Function in Basic Communication System
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Input Transducer – convert input signal, s(t) in electrical forms. eg: microphone.
Transmitter – involve modulation process – convert modulating signal, mtx(t) to modulated signal, ptx(t). And finally transmit the signal.
Transmission medium – connecting the transmitter and the receiver that enable the modulated signal, ptx(t) propagate through the medium.
Receiver – receive the modulated signal, prx(t) and then convert the signal to modulating signal, mrx(t) through the process called demodulation.
Output Transducer – convert the modulating signal, mrx(t) to its original forms (output signal), r(t) that is useful to the users. eg: loud speaker.
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Transmission Medium (Guided)Twisted pairUnshielded Twisted Pair (UTP)Shielded Twisted Pair (STP)
Coaxial
Fiber Optic
Waveguide
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100 Mbps is how many bits per sec?
Which is bigger: 10,000 Mbps, 0.01Tbps or 10Gbps?
Wireless channel capacity:
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Concept of Time Domain and Frequency DomainAll signals exist in real world in time domainOscilloscopes shows signals as a function of timeBut it is yet again the representation of data as a
function of time
We can view the same information as a function of some other variable which may have a useful meaning
In analysis composite signals are hard to analyzeHence we use frequency domain
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WHAT IS FREQUENCY SPECTRUM
IT CONSISTS OF ALL FREQUENCIES CONTAINED IN THE WAVEFORM AND THEIR RESPECTIVE AMPLITUDE IN THE FREQUENCY DOMAIN.
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Another Look
Time Domain Sine wave viewed as an impulse function in frequency domain
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Spectrum Analyzer
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Oscilloscope vs Spectrum Analyzer
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10
0M
Hz
Waveguide
Coaxial Cable
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Optical Fiber
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Line-of-sight radio
Skywave radio
Groundwave radio
Wavelength
Frequencydesignations
Transmission media
Propagation modes
Representativeapplications
Frequency
Laser beam
100km 10km 1km 100m 10m 1m 10cm 1cm 10-6m
Tele
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Concept of Bandwidth IT IS THE DIFFERENCE BETWEEN
THE HIGHEST FREQUENCIES AND THE LOWEST FREQUENCIES OF THE INPUT SIGNAL FREQUENCIES (fB = 2fm ).
The bandwidth of a communication signal bandwidth of the information signal.
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Data (nonelectrical)
Electrical Waveform
Without any shift in the range of frequencies of the signalThe signal is in its original form, not changed by modulation.
Baseband is the original information that is to be Sent.
It starts from zero and to some specific frequency
WHAT IS BASEBAND SIGNAL ?WHAT IS BASEBAND SIGNAL ?
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WHAT IS PASSBAND SIGNAL ?WHAT IS PASSBAND SIGNAL ?
After modulation, the original baseband signal is moved to a range of frequency which far more higher than the baseband signal
So it’s a range of frequency shifted after modulation
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What is Modulation MODULATION IS THE PROCESS OF
CHANGING SOME PROPERTYOF THE INFORMATION SOURCES INTO SUITABLE FORM FOR TRANSMISSION THROUGH THE PHISICAL MEDIUM/CHANNEL
“Process of coverting baseband signal into passband signal is called modulation”
It is performed in the Transmitter by a device called Modulator. 26
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Transmitter
Carrier
Information to be transmitted
(Baseband signal)
Transmittedsignal
Channel
Receivedsignal
Receiver
Recovery of information
Typical Modulation
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Modulation
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TYPE OF MODULATION
Amplitude Modulation (AM)
Frequency Modulation (FM)
Phase Modulation (PM)
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TYPE OF MODULATION
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Need for Modulation Channel assignment (various information
sources are not always suitable for direct transmission over a given channel)
Efficient Utilization of bandwidth and multiplexing
Reduce noise &interference
Reduction in antenna size31
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What is Demodulation DEMODULATION IS THE REVERSE
PROCESS OF MODULATION BY CONVERTING THE MODULATED INFORMATION SOURCES BACK TO ITS ORIGINAL INFORMATION (IT REMOVES THE INFORMATION FROM THE CARRIER SIGNAL).
It is performed in the Receiver by a device called Demodulator.
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Example If human voice frequencies contain
signals between 300 Hz and 3000 Hz, a voice frequency channel should have bandwidth equal or greater than 2700 Hz.
a communication channel cannot propagate a signal that contains a frequency that is changing at a rate greater than the Channel Bandwidth.
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Transmitter Block Diagram
Lecture 27 34
Signal
SourceModulator
Power
Amplifier
Antenna
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AM TransmitterBlock diagram
In Modulator the audio modulates the RF amplitude
RFoscillator
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ModulatorThe modulator converts the frequency of the
input signal from the audio range (0-5kHz) to the carrier frequency of the station (i.e.. 605kHz-615kHz)
Lecture 27 36
frequency
5kHz
Frequency domain representation of input
Frequency domain representation of output
frequency
610kHz
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Receiver Block Diagram
Lecture 27 37
RF
Amplifier
IF
Mixer
IF
Amplifier
Envelope
Detector
Audio
Amplifier
Antenna
Speaker
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Trigonometric Fourier SeriesA signal g(t) in the interval
t1 t t1+T0 can be represented by
1
000 )sin()cos()(n
nn tnbtnaatg 011 Tttt
01
1
)(1
00
Tt
t
dttgT
a
01
1
)cos()(2
00
Tt
t
n dttntgT
a
01
1
)sin()(2
00
Tt
t
n dttntgT
b T0 = 2 / 0
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Reduced Form of Trigonometric Fourier SeriesOr, in the compact form
If g(t) is even then bn = 0 for all nIf g(t) is odd then an=0 for all n.
1
00 )cos()(n
nn tnCCtg
;22nnn baC
n
nn a
b1tan
011 Tttt
C0 = a0 ;
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Remarks on Fourier Series (FS) Representations
The frequency 0= 2/T0 is called the fundamental frequency and the multiple of this frequency n0 is called the nth harmonic.
FS of g(t) is equal to g(t) over the interval t1 t t1+T0 only.
The FS for all t is a periodic function of period T0 in which the segment of g(t) over the interval t1 t t1+T0 repeats periodically.
If the function g(t) itself is periodic with period T0 then the FS represents g(t) for all t.
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Exponential Fourier Series
Dn is related to Cn and n as
| Dn | is called the amplitude spectrum of the signal.
Dn is called the phase spectrum of the signal.
They provide a frequency-domain representation of the signal.
011 Tttt
)0(
000)(
nn
tjnn
n
tjnn eDDeDtg
dtetgT
DT
tjnn
0
0)(1
0
nnn CDD2
1|||| nnn DD
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NoteMaterial for today was from Chapter 1 text book
This concludes Chapter # 1
Concepts of time, frequency, baseband, passband, bandwidth and spectrum are not exclusively available in chapter 1 but are available in subsequent chapters buried within text.
Questions ????