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ECE4058 Digital Communication
Digital Communication
Electronics and Communication EngineeringHanyang University
Haewoon Nam
Lecture 1
(ECE4058)
1
ECE4058 Digital Communication
Course Outline
• Lecture Time and Room:– Mon. 10:30am - 12:00pm, Eng. Bldg 1, Room 302 (Y05-302)– Tue. 02:30pm - 04:00pm, Eng. Bldg 1, Room 303 (Y05-303)
• Office Hours: Wed. 10:00am - 12:00pm or email for appointment
• Instructor: Haewoon Nam• Email: [email protected]• Office: Engineering Building 3, Room 304
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ECE4058 Digital Communication
Course Outline
• Textbook:1. “Communication Systems Engineering”” by John G. Proakis and M. Salehi,
Pearson/Prentice Hall2. “Introduction to Analog and Digital Communications”, by Simon Haykin and
Michael Moher, Wiley
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ECE4058 Digital Communication
Course Outline
• Prerequisites: – ECE3008 Signals and Systems– ECC3004 Theory of Random Variables– ECC1015 Communication System I– Students who have not completed the prerequisites may still take this course.
Please discuss it with the instructor.
• Homeworks– Tools: Matlab and Simulink
• Grading:– Midterm exam 30%– Final exam 30%– Attendance and participation 10%– Project 20%– Homework 10%
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ECE4058 Digital Communication
Course Schedule
• Week 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Course introduction• Week 2 . . . . . . . . . . . . . . . . . . Digital Modulation in an AWGN Baseband Channel• Week 3 . . . . . . . . . . . . . . . . . . Digital Modulation in an AWGN Baseband Channel• Week 4 . . . . . . . . . . . . . . . . . . Digital Modulation in an AWGN Baseband Channel• Week 5 . . . . . . . . . . . . . . . . . . Digital Modulation in an AWGN Baseband Channel• Week 6 . . . . . . . . . . . . . . . . . . Digital Modulation in an AWGN Baseband Channel• Week 7 . . . . . . . . . . . Transmission of Digital Information via Carrier Modulation• Week 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Midterm exam• Week 9 . . . . . . . . . . . Transmission of Digital Information via Carrier Modulation• Week 10 . . . . . . . . . . Transmission of Digital Information via Carrier Modulation• Week 11 . . . . . . . . . . Transmission of Digital Information via Carrier Modulation• Week 12 . . . . . . . . . . . . . . . . . . . . . . . . . . . Comparison of Modulation Methods• Week 13 . . . . . . . . . . . Digital Transmission through Bandlimited AWGN Channels• Week 14 . . . . . . . . . . Digital Transmission through Bandlimited AWGN Channels• Week 15 . . . . . . . . . . . Digital Transmission through Bandlimited AWGN Channels• Week 16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Final exam
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ECE4058 Digital Communication
Data Communications
• Elements of communication systems– Source of information
• video, audio, text message, file data– Transmitter– Channel
• radio frequency, cable, visible light, underwater– Receiver
6[Ref] Introduction to Analog and Digital Communications,
by Haykin and Moher, Wiley
ECE4058 Digital Communication
Underlying Theories of Communications
• Modulation Theory– Sinusoidal carrier wave
• Whose amplitude, phase, or frequency is the parameter chosen for modification by the information-bearing signal
– Periodic sequence of pulses• Whose amplitude, width, or position is the parameter chosen for modification
by the information-bearing signal– The issues in modulation theory
• Time-domain description of the modulation signal.• Frequency-domain description of the modulated signal• Detection of the original information-bearing signal and evaluation of the
effect of noise on the receiver.
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ECE4058 Digital Communication
Underlying Theories of Communications
• Fourier Analysis– Fourier analysis provides the mathematical basis for evaluating the
following issues• Frequency-domain description of a modulated signal, including its
transmission bandwidth• Transmission of a signal through a linear system exemplified by a
communication channel or filter• Correlation between a pair of signals
• Probability Theory and Random Processes– Probability theory for describing the behavior of randomly occurring
events in mathematical terms– Statistical characterization of random signals and noise.
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ECE4058 Digital Communication
Underlying Theories of Communications
• Detection Theory– Signal-detection problem
• The presence of noise• Factors such as the unknown phase-shift introduced into the carrier wave
due to transmission of the sinusoidally modulated signal over the channel– In digital communications, we look at
• The average probability of symbol error at the receiver output• The issue of dealing with uncontrollable factors• Comparison of one digital modulation scheme against another.
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ECE4058 Digital Communication
Analog and Digital Signals
• Analog– Most of the signals in daily life are analog in nature.– Signals are functions of time, frequency, and space and usually
take values in a continuous range.– The signals can be directly processed in its analog form.
• Digital– Signals are represented by discrete variables and discrete time.
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Analog input signal
Analog output signal
Analog signalprocessor
Digitalinput signal
Digitaloutput signal
Digital signalprocessor
D/Aconverter
A/Dconverter
Analog output signal
Analog input signal
ECE4058 Digital Communication
Comparison of Digital and Analog
• Advantages of digital signal processing– Easy (software) and stable processing by microprocessor– Easily stored in memory without deterioration– Lower cost due to VLSI technology (lower costs of memory, etc)– Efficient resource management (e.g. data compression)– More robust data management (e.g. coding)
• Limits of digital signal processing– Speed of operation is limited by A/D and D/A converters and
digital signal processors
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Digitalinput signal
Digitaloutput signal
Digital signalprocessor
D/Aconverter
A/Dconverter
Analog output signal
Analog input signal
ECE4058 Digital Communication
Classification of Signals
• Continuous-Time versus Discrete-Time signals• Continuous-Valued versus Discrete-Valued signals• Deterministic versus Random signals
– Deterministic signal• All past, present, and future values of the signal are known precisely with no
uncertainty.
– Random signal• Signals can not be described accurately (noise signals, seismic signal, etc).• Probability and stochastic theory provides the mathematical framework for
the theoretical analysis of random signals.
• Periodic versus Aperiodic signals
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T
ECE4058 Digital Communication
Classification of Signals• Continuous and discrete signals
– Continuous-time andcontinuous-valued signal
– Discrete-time andcontinuous-valued signal
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f(t)
f(n)
t
n
– Continuous-time and discrete-valued signal
– Discrete-time and discrete-valued signal
g(t)
t
g(n)
n
Sampling
Quantization
ECE4058 Digital Communication
Sampling Process
• Instantaneous Sampling and Frequency-Domain Consequences– Sample the signal g(t) instantaneously and at a uniform rate,– Instantaneously (ideal) sampled signal
• The signal obtained by individually weighting the elements of a periodic sequence of Dirac delta functions :
– Reproduce the relationships listed at the bottom of the right-hand side• The process of uniformly sampling a continuous time signal of finite energy
results in a periodic spectrum with a repetition frequency equal to the sampling rate.
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∞
−∞=
−=n
ss nTtnTgtg )1.5()()()( δδ
∞
−∞=
∞
−∞=
∞
−∞=
=−=−⇔−n n
ssn
ssss fGfnTjnTgmffGfnTtnTg )2.5()()2exp()()()()( δπδ
ECE4058 Digital Communication
Sampling Process
• What is sampling?
• Nyquist sampling theorem
• Aliasing problem
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ECE4058 Digital Communication
Sampling Theorem
• Aliasing problem– The phenomenon of a high-frequency component in the spectrum of
the signal seemingly taking on the identify of a lower frequency in the spectrum of its sampled version.
– To combat the effects of aliasing in practices • Prior to sampling : a low-pass anti-alias filter is used to attenuate those
high-frequency components of a message signal that are not essential to the information being conveyed by the signal
• The filtered signal is sampled at a rate slightly higher than the Nyquist rate.– Physically realizable reconstruction filter
• The reconstruction filter is of a low-pass kind with a passband extending from –W to W
• The filter has a non-zero transition band extending form W to fs-W
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ECE4058 Digital Communication
Sampling Theorem
• Aliasing problem
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ECE4058 Digital Communication
Quantization Process
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ECE4058 Digital Communication
Announcement and Assignment
• Reading assignment– Fourier Transform chapter of Signals and Systems– Details of convolution– Relationship between time and frequency– Analog-to-digital conversion (Chapter 7)
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