CSN200 Introduction to Telecommunications, Winter 2000 Lecture_13 Communication Basics
Communication Basics:

Signals:

Communication happens in the form of signals.
Signals are transmission of energy (mechanical, electrical or light) through appropriate
media.
A signal that is constant and changed once conveys single information.
The more changes in the signal, the more information that the signal can convey.
For example, a push can mean one thing and removing it can mean another thing.

But how do we send more information than just these two?
We can do that by varying the amplitude, i.e., a strong push or a light push could have two
different meaning.
Or, a rate of change of push, i.e. 10 pushes per minute or 1 push per minute could have different
meaning too.
Or, even phase, i.e., pushing at a different angle could have different meaning too.

Amplitude, frequency and phase are the attributes of a signal that changes with time.

This pushing, transfer of mechanical energy has a limit. How many different amplitude, rate and
phase of pushing can we transmit and distinguish (receive)? God gave us organs like vocal cord
which can create higher rate of pushing and ears to sense that.
Higher the rate of pushing the more information it can convey and even the mixing of these
different rate could mean different information. And our vocal cord is able to do that as well.
We have even media (air) which will carry that signal far, so we don't have to stay close to
communicate. But that has a limit too.

Then we came out with a solution of converting this pressure wave to electrical signals and then
transmitting over long distances.

Speakers:
Moving coil speakers - public address systems
Piezoeletric speakers - Newer telephones, toys

An electromagnetic signal is a function of time, but it can also be expressed as a function of
frequency.
The frequency-domain view of a signal is far more important to an understanding of data
transmission than a time-domain view.
The characteristics and quality of a data transmission are determined by both the characteristics
of the medium and the characteristics of the signal.

Time-domain concept:
Viewed as a function of time, an electromagnetic signal can be either analog or digital.
An analog signal is one in which the signal intensity varies in a smooth fashion over time. There
are no breaks or discontinuities in the signal.
A digital signal is one in which the signal intensity maintains a constant level for some period of
Information
Electromagnetic
signal
Lecture 13.doc Page 3 (9)
CSN200 Introduction to Telecommunications, Winter 2000 Lecture_13 Communication Basics
time and then changes to another constant (discrete) level.

Analog
Time, t
Signal
Amplitude,
A

CSN200 Introduction to Telecommunications, Winter 2000 Lecture_13 Communication Basics
Amplitude: Frequency:

Phase:
Lecture 13.doc Page 5 (9)