Course Overview
1. ELEMENTS OF A DIGITAL COMMUNICATION SYSTEM
(Chapter‐1 & Chapter‐2)
2. SIGNALS, SYSTEMS, AND SPECTRAL ANALYSIS (Chapter‐3)
3. Analog‐to‐Digital Conversion (Chapter‐5)
4. DIGITAL PULSE MODULATION (Chapter‐5)
5. Baseband Digital Transmission (Chapter‐6)
6. Passband Digital Transmission (Chapter‐7)
7. Synchronization (Chapter‐8)
8. ERROR‐CONTROL CODING (Chapter‐10)
Course Overview
1. ELEMENTS OF A DIGITAL COMMUNICATION SYSTEM
(Chapter‐1 & Chapter‐2)
2. SIGNALS, SYSTEMS, AND SPECTRAL ANALYSIS (Chapter‐3)
3. Analog‐to‐Digital Conversion (Chapter‐5)
4. DIGITAL PULSE MODULATION (Chapter‐5)
5. Baseband Digital Transmission (Chapter‐6)
6. Passband Digital Transmission (Chapter‐7)
7. Synchronization (Chapter‐8)
8. ERROR‐CONTROL CODING (Chapter‐10)
Required Textbook/Materials
• Ali Grami, “Introduction to Digital Communications”, Elsevier Inc., 2016
• Bernard Sklar, Digital Communications, Fundamentals and
Applications, Prentice Hall PTR, Second Edition, 2001. ISBN: 0‐13‐
084788‐7.
• John G. Proakis and Masoud Salehi, “Digital Communications, 5thed.,”
McGraw Hill, Fifth Edition, 2008. ISBN: 978‐0‐07‐295716‐7.
Supplemental Books and Materials
• John G. Proakisand MasoudSalehi, “Communication Systems Engineering,
2nd ed.”, Prentice Hall, 2002. ISBN: 0‐13‐061793‐8.
• A. Bruce Carlson, P.B. Crilly, “Communication Systems, 5th ed.”, McGraw‐
Hill, 2010. ISBN: 978‐0‐07‐338040‐7.
• https://www.tutorialspoint.com/digital_communication/digital_communic
ation_digital_modulation_techniques.htm
LECTURE 1
ELEMENTS OF A DIGITAL COMMUNICATION SYSTEM
SIGNALS, SYSTEMS, AND SPECTRAL ANALYSIS
Communications System
Sklar’s Communications System
Digital Communications System
• The digital data are usually a sequence of Zeros (0) and Ones (1).
• The digital modulator may transmit 1 coded information bit that may simply
map the binary digit (0) into a waveform s0(t) and the binary digit (1) into a
waveform s1(t).
We call this binary modulation (M=2).
• The modulator may transmit b coded information bits at a time by using
M=2b that simply mapped as si(t), i= 0, 1, ..., M‐1.
We call this M‐ary modulation (M>2).
• Depending on the nature of the communication channel, data can suffer from
one or more of certain channel losses including Noise, Attenuation, Distortion,
and Interference.
• We need to generate a signal that should match the characteristics of the
channel, and it should be able to resist the channel losses.
Simplified Communications System
011010 01101011
011010 01101011
• Format: making the message compatible with digital processing
• Source Coding: efficient descriptions of information sources
• Channel Coding: signal transformation enabling improved reception performance
after expected channel impairments
• Modulation: formation of the baseband waveform
• RF Mixing: frequency domain translation of baseband signal to passband signal
• Transmit/Receive: RF Amplifiers and Filters
Communication Channel
• The channel greatly effects received RF signals
Frequency,
Affect
Bandwidth,
Transmitted Signal Power,
RF Propagation,
Attenuation,
Effect
Nonlinear Distortion,
Multipath,
Direction,
Signal‐to‐Noise Ratio (SNR), Bit Error Rate (BER),
Metrics
Impact
Signal‐to‐Interference Ratio (SIR), Maximum Data Rate
Minimum Detectable Signal Level (MDS).
Received Signal
• The receiver must extract the original message as best as
possible!
• Multiple signals with similar channel characteristics may be
present.
• The RF channel(s) must be allocated and efficiently utilized.
Frequency band assignments and regulations (power,
direction, etc.).
Signal modulation structures have different characteristics.
Why Digital?
• Good processing techniques are available for digital signals, such as
‐ Storing Capability
‐ Inexpensive with respect to the analogue
‐ Using of repeaters make the system easy to regenerate the distorted
signal
‐ Privacy and security through the use of encryption
‐ Data compression, error detection & correction
‐ Flexible hardware implementation (just by changing the program of
the system)
‐ Easier and more efficient to multiplex several digital signals
‐ Better overall performance
Disadvantages of Digital Communication Systems
1. Requires larger bandwidth.
2. Requires reliable “synchronization”. Without this
synchronization an error will occur.
3. High power consumption due to multiple stages.
4. Complex circuit.
5. Requires A/D conversions at high rate.
6. Probability of error or Bit Error Rate.
Sklar’s Communications System
Classification of Signals
1‐ Continuous‐Value and Discrete‐Value Signals
2‐ Continuous‐Time and Discrete‐Time Signals
3‐ Analog and Digital Signals
4‐ Deterministic and Random Signals
5‐ Real and Complex Signals
6‐ Periodic and Nonperiodic Signals
Classification of Signals
7‐ Even and Odd Signals
8‐ Energy and Power Signals
9‐ Causal and Noncausal Signals
10‐ Time‐Limited and Band‐Limited Signals
11‐ Baseband and Bandpass (Passband) Signals
Classification Of Systems
1‐ Baseband and Passband Systems
2‐ Invertible and Noninvertible Systems
3‐ Lumped and Distributed Systems
4‐ Adaptive and Fixed Systems
5‐ Systems with or without Feedback
6‐ Systems with or without Memory
Classification Of Systems
7‐ Systems with Single/Multiple Inputs and
Single/Multiple Outputs
8‐ Passive and Active Systems
9‐ Causal and Noncausal Systems
10‐ Continuous‐Time and Discrete‐Time Systems
11‐ Power‐Limited and Band‐Limited Systems
Classification Of Systems
12‐ Stable and Unstable Systems
13‐ Linear and Nonlinear Systems
14‐ Time‐Invariant and Time‐Varying Systems
15‐ Linear Time‐Invariant (LTI) Systems
Baseband and Bandpass Signals
The baseband signal may be sent using a wired
connection or network to a receiver.
Bandwidth Consideration
Bandwidth Consideration
LECTURE 2
ANALOG‐TO‐DIGITAL CONVERSION
ANALOG‐TO‐DIGITAL CONVERSION
Formatting
• Insure that the message is compatible with digital processing
• Transmit formatting is where the source information is
translated into digital symbols
• When data compression is also employed, the process is
called source coding.
Data Format
• A character consists of
– one start bit (0‐level)
– 7 to 8 data bits (often, an ASCII character plus a parity bit)
– an optional parity bit
– one or two stop bits (1‐level)
– least significant bit is transmitted first
– most significant bit is transmitted last
Textual Data
• 5‐bit coding – Baudot Code: 32 characters, alphabet plus 6
• 7‐bit coding – ASCII Code: American Standard Code for
Information Interchange
– Originally designed for telegraph; therefore, extra fields
• 8‐bit coding – EBCDIC Code: Extended Binary Coded Decimal
Interchange Code
– IBM system
• 16‐bit coding – Unicode
Code may be sent serially with start, parity and stop bits
Code may be structured as words/symbols
Sampling
Sampling Process
Ideal – An impulse at
each sampling instant.
Natural – A pulse of
short width with varying
amplitude.
Flat Top – Uses sample
and hold, like natural
but with single
amplitude value.
Sampling Process
1. Under‐sampling and Aliasing Effect
Under‐sampling occurs when a signal is sampled too
slowly (i.e., 𝑓 Nyquist rate . This phenomenon called
Aliasing or frequency overlapping or fold‐over distortion
or spectral folding. This frequency overlapping prevents
the recovery of the original signal.
2. Up‐sampling and
When a signal cannot be sampled much above the
Nyquist rate, and yet more samples are needed, a
process known as up‐sampling or interpolation is
required.
3. Oversampling
When a signal is sampled at a rate much higher than the
Nyquist rate, the process is then called oversampling or
decimation. Oversampling helps avoid aliasing and
reduces noise.
Quantization
Quantization
Uniform Quantization
There are two types of uniform
quantization.
o Mid‐Rise type
o Mid‐Tread type.
Non‐Uniform Quantization
Quantization: (Example)
Encoding
Data Encoding Types
1‐ Polar line codes
o Polar NRZ
o Polar RZ
2‐ Unipolar NRZ
NRZ
3‐ Bipolar Line Codes
4‐ Manchester Line Codes
Manchester
One Zero
