Faculty of Engineering
Alexandria University
Name: Hany Hamza Mohamed Salah
ID: 19016833
Submitted to: Dr. Elsayed Yousef
Why did the author choose this cover?
The purpose of the book is to provide coverage of digital communication
systems. Though the emphasis is on this subject, necessary analog
fundamentals are also included since analog waveforms are used to carry
digital data and transmit it. The book discusses these techniques in terms
of a unified structure, which is the block diagram in the cover letter, and
is also included at the beginning of each chapter. Blocks in the diagram
are discussed in depth when appropriate to cover the subject of that
chapter, so that the student has an idea about the big picture (the whole
structure) while also developing in-depth knowledge about some of its
elements. Signals and key processing steps are traced from the
information source through the transmitter, channel, receiver, and
ultimately to the information sink. Signal transformations are organized
according to nine functional classes: Formatting and source coding,
Baseband signaling, Bandpass signaling, Equalization, Channel coding,
Multiplexing and multiple access, Spreading, Encryption, and
Synchronization.
The block diagram illustrates the flow of a signal in a digital
communication system. The upper part is basically the transmitter, and
all of the processing steps that the signal goes through, while the lower
part is the receiver where all these processes are reversed.
The steps are as follows:
1. The input information is converted to binary bits, which are then
grouped to form digital messages.
2. Encryption adds a security layer to the data to prevent
unauthorized access.
3. Channel encoding adds redundant parts to the bit stream, to make it
more resistant to loss of data.
4. Multiplexing and multiple access allows multiple types of data to
be sent over the same channel and/or multiple users to be able to
5.
6.
7.
8.
access this data, using techniques like frequency division
multiplexing and frequency division multiple access.
A modulator converts this digital signal to an analog signal that
can then travel through a channel, by superimposing the signal on a
carrier waveform.
Frequency spreading can decrease the risk of interference on the
signal, producing a clean signal.
The channel carries the information, whether it be a piece of wire
or air, in case of wireless data.
Synchronization is necessary so that all these processes coordinate
with each other, and the transmitter coordinates with the receiver
and knows when to send, receive and/or process the signal.
All the above steps are then performed in reverse in the receiver, by
means of frequency despread, demodulators, decoders and decryptors, to
finally reproduce the original signal at the information sink.