Mokhtar A. Aboelaze
. CSE 2026 ext. 40607. Digital
Communication 2nd edition, B. Sklar. 15% quizzes (3 ). 10% project. 30%
Midterm.
COSC4214 Digital Communication York University Fall 2005 Based on class notes by Prof: Amir Asif
CSE4214 Digital Communication. Instructor Text Assessment
Office Hours
Mokhtar A. Aboelaze
[email protected] CSE 2026 ext. 40607 Digital Communication 2nd edition, B. Sklar 15% quizzes (3 ) 10% project 30% Midterm 45% Final Tuesday and Thursday 11:00 – 1:00pm
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Course Outline
Objective
Introduce a mathematical representation for noise
Process a random process such as noise with a linear system
Learn about baseband communications: single signal transmission at low frequencies (Baseband Modulation)
Learn about bandpass or broadband communications: multiple signal transmission at high frequencies (Bandpass Modulation)
Detect signal in the presence of noise (Matched filtering)
How to control error using error detection and correction techniques (Channel coding)
Learn advance topics like Spread Spectrum techniques
Demystify terminology !!!!!!
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Introduction
• • • • •
Why Digital Less distortion (no error accumulation) Multiplexing is easier than analog. Hardware is cheaper and more flexible Down side: non-graceful degradation, very SP intensive, and have to worry about synchronization
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DCS • The previous figure shows the different stages(operations) in a digital communication system. • Some of these are essential: Format, Pulse modulation, and bandpass modulation. • The rest is optional, we may or may not perform them based on the type of system. • We briefly explain the following blocks
DCS (essential) • Formatting transforms the source information into bits (binary or M-ary). • Pulse modulation: Generally modulation is message symbols are converted into waveforms that are suitable for transmission. • Pulse modulation means to changes the pulses (1’s and 0’s) to a baseband (its spectrum extends from 0 to x Hz) waveform.(PCM, line code)., M-ary pulse modulation (PAM, ..)
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DCS (essential) • Bandpass modulation: That is required especially for RF transmission. • The baseband signal is frequency translated by a carrier wave to a much higher frequency (more suitable for propagation in the channel). The received signal is (h is the channel impulse response, n is noise) • r (t ) = s (t ) ∗ h(t ) + n(t )
DCS (essential) • Synchronization: Synchronization can be done on more than one level. • The demodulator must know the beginning and end of each symbol (symbol or bit synchronization). • Then, we must know the beginning and end of every frame/packet/message. • Finally,network synchronization is the synchronization of spatially spread processes (users) to access network resources.
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DCS (optional) • Source coding: source coding does A/D conversion and may remove redundant information (to save bandwidth). • Usually either source coding or formatting will be used • Encryption: encryption is used to hide information, or to prevent it from being altered by an intruder.
DCS (optional) • Channel coding: channel coding is used to reduce the probability of error (bit error). • Waveform coding, or structure sequences. • Waveform coding is the use of a new waveform to improve detection and reduce errors. • Structured sequences is the addition of more bits (or modification of the existing bits) in order to make error detection (or correction) easier (block coding, convolution coding, turbo coding).
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DCS (optional) • Multiplexing/multiple access: both involve sharing the channel between many users. • Multiplexing takes place locally and uses a priori known algorithm (FDM, TDM, CDM). • Multiple access takes place remotely and usually uses an adaptive algorithm, also require some overhead.
DCS (optional) • Spreading: originally developed for military applications to combat jamming and to prevent eavesdropping. • Spread spectrum techniques are used in cellular communication (spreading in frequency, time, or both). • Also used to share the channel between many users.
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Classification: Deterministic vs. Random Deterministic Signals: Defined for all time No uncertainty with respect to the value of the signal Represented using a mathematical expression, e.g., x(t) = sin(5πt + 30o). Random Signals: Are not known accurately for all instants of times Different observations may lead to different results Statistical properties such as mean, variance, or probability density function (pdf) are used to define the random signal
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Classification: Periodic vs. Aperiodic
Periodic signals: A periodic signal x(t) is a function of time that satisfies the condition x(t) = x(t + T0) for all t where T0 is a positive constant number and is referred to as the fundamental period of the signal Fundamental frequency (f0) is the inverse of the period of the signal. Nonperiodic (Aperiodic) signals: are those that do not repeat themselves.
Classification: Analog vs. Discrete • Analog: is a continuous function and is defined for all t
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Classification: Analog vs. Discrete • Discrete: is defined only at discrete times x(kT) CT Signal
Sampling
DT Signalx[ k ] =
x(t ) t =kT = sinc(kTs ) = s
sin( πkTs ) πkTs
k
Classification: Analog vs. Discrete • Digital: Defined only at discrete times, and the magnitude is restricted to a finite set of values. CT Signal
Sampling
DT Signal
Quantiza tion
Digital Signal
k
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