introduction to digital communication

1. Digital Communication
Systems
Dr.Eng.
Nashaat Mohamed Hussein Hassan
First Semester 2022-2023
Lecture:
References: Principles of Electronic Communications Systems
Louiz-Frenzel
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2. Ch1
Introduction to Digital Communication
Systems
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3.  Introduction
Signal Types
Communications Types
 Advantages and Disadvantages
Block Diagram of Digital communication Systems
 Source Coding
Presentation Outline
Introduction to Digital
Communications
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4. Signal Types
 Analog Signal: it’s a continuous values in continuous times signal, at this signal
can not be used with digital systems until convert it to be in suitable form.
Analog Signal Digital Signal
Introduction to Digital
Communications
 Digital signal: it’s a discrete values in discrete time signal , at this signal can be
used directly with digital systems.
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 Signal Types: signals that are used in system communications divided into two
types .

5. Types of Analog and digital signal
Introduction to Digital
Communications
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 Analog and digital signal can be founded in varies forms according to
it’s value of the amplitude and it’s time period :
1- according to it’s values:
- deterministic signals : signals with deterministic amplitude values.
- random signals: signals with random values.
2- according it’s period time :
- periodic signals: are repeated in equivalent times (same forms).
- aperiodic (non periodic signals) signals: are repeated with different
forms.

6. 2-Digital Communications Systems
1- Analog Communication Systems
Communications Systems Types
Introduction to Digital
Communications
 Respect to the type of signals the communication
systems can be divided into two types:
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7. Introduction to Digital
Communications
Advantages and Disadvantages of Digital
Communications
1. Simplicity of regeneration of signals that are effected by the noises and
attenuation through the communication channels.
2. Easily of realizing an advanced processing of signals (encoding with it’s
types, security, compression, and so on).
3. The hardware components that are used in digital communications are more
simple, confidante, and flexible than that used in analog communication.
4. Simplicity in using the multiple systems (TDM, CDMA(Code Division Multiple
Access)) with the comparison of the multiple systems that are used in analog
communications such as FDM.
5. Low of the affection with the noises because the receiver device is only
treatment with two values 0 or 1.
6. Ability in sending and receiving different types of information at the same
 Advantages
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8. Introduction to Digital
Communications
Advantages and Disadvantages of Digital
1. High quality when receiving the information
2. More suitable and easily in using with computers and compression systems.
3. Low cost of resources
 Advantages
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9. Introduction to Digital
Communications
Advantages and Disadvantages of Digital
1. It’s necessary to be a synchronization between transmitter and receiver.
2. it’s necessary to convert the analog signals to digital signals .
3. it’s not suitable to use with the analog devices.
 Disadvantages of digital communication systems
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10. General Block Diagram of a Digital Communication
System
Introduction to Digital
Communications
TX
Formatting Source
Coding
Channel
Coding
Multiplexing
Band-pass
Modulation
RX
Reformatting Source
Decoding
Channel
Decoding
Demultiplexing
Band-pass
Demodulation
Transmitter Process
Receiver Process
General Block Diagram of a Digital Communication System
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11. Introduction to Digital
Communications
General Block Diagram of a Digital Communication
System
1. Information Source: it’s the source of information that is needed to
transmit or send through the different communication systems, information
source such as text, voice, music, image, video signals.
2. Formatting: at this stage a converting of the information into a form (integer
values) that is suitable to transmit it through a digital communication system is
done . At this stage an analog to digital converter is done (sampling and
quantization process are realized).
3. Source Encoding: at this stage a converting of the representation of
information is done by means of removing of information that is not needed
(redundancy of information) to reduced the information that is needed to store
or transmit (compression process). 11

12. Introduction to Digital
Communications
General Block Diagram of a Digital Communication
System
4. Channel encoding : another encoding process of the information will be
done at this stage to protect it from the different noises that is created during
the flowing of information through the communication channels.
5. Multiplexing: at this stage is allowed to transmit a multiple signals from
different sources through the same channel and at the same time. Usually is
used the methods Time Division Multiplexing (TDM) and Code Division
Multiple Access (CDMA).
6. Band-pass Digital Modulation: at this stage a converting of the digital
information into a digital waves is done to be suitable for sending through the
communication. Actually, a radio frequency is used for wireless
communications and Audio frequency is used for wire communication. 12

13. Introduction to Digital
Communications
General Block Diagram of a Digital Communication
System
7. Band-pass Digital Demodulation: an inverse process of the previous process
is done at this stage by means a coming back again (recovering, detecting,
extracting) of the digital information instead of the wave information by using a
suitable detection method.
8. Demultiplexing: a distribution of the multiple sending signals to it’s different
sources is don at this stage.
9. Channel Decoding : exactly, an inverse operation of the channel encoding
process is done at this stage, where is a coming back of the original
information that is encoded to prevent the loss which my be happens through
the transmission process of the communication channels.
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14. Introduction to Digital
Communications
General Block Diagram of a Digital Communication
System
10. Source Decoding: a coming back of the original form of the digital
information that is changed in the step of source encoding to make a
compression of the information. A decompression process is done at this
stage
11. Data Reformation: a digital to analog converting process is done at this
stage.
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