409 Lecture Note 2018 - Intro
409 Lecture Note 2018 - Intro
409 Lecture Note 2018 - Intro
EEE 409:
Communication
Principles
Lecture Note
Communication Principles Assume That The Students Have Some
Basic Fundamental Knowledge Of Electrical & Electronic Circuit
Theory and Linear System Analysis. The Major Goal Of The Course
Is To Teach Students About Some Of The Basic Principles
Underlying The Analysis, Design And Operation Of Communication
Systems. The Course Is Structured To Provide Detailed Knowledge
of How Information Is Processed At The Transmitter, Transferred
Over A Noisy Channel And Retrieved At The Receiver With Minimal
Degradation. Thus, One of The Aims of Signal Analysis And
Processing Is To Receive A Replica Of The Transmitted Signal At
The Receiver. Different Types Of Signal Modulation and
Demodulation Techniques Are Discussed.
COURSE OUTLINE
◊ Review of Baseband Signals and Systems Analysis: Fourier series, Fourier Transforms, Impulse response,
frequency response, distortion and group delay.
◊ Comparison of AM systems: Double Sideband Suppressed Carrier (DSBSC), Single Sideband (SSB),
Vestigial Sideband (VSB)
◊ Angle Modulation and Demodulation: Frequency Modulation (FM) and Phase Modulation
◊ Quantization
◊ Companding
◊ Pulse Modulation: Pulse Amplitude Modulation (PAM), Pulse Width Modulation (PWM) and Pulse Code
Modulation (PCM)
○ http://www.integral-calculator.com/
COMMUNICATION PRINCIPLES
• To give you basic understanding of a communication system, Figure 1 shows the typical elements of a
communication system.
Communication system
Source of User of
Information Message Transmitter Receiver Estimate Information
signal of message
signal
Communication systems can be classified based on the nature of output of the information source and
the types of modulation scheme utilised
• Basic modes of Communications include Telephony, Radio or Television Broadcasting, Radar, Mobile
Communication, Computer communication, etc.
• Sources of information: The message originates from the information source. Messages can be in the
form of words, code, symbols, sound signal etc. The function of the information source block is to
produce the required message to be transmitted.
• Transmitter: It comprises of blocks of electrical and electronic components that convert the message
signal into a form suitable for transmission over the communication channel. The conversion is achieved
by succession of processes that include modulation that will be studied in details in this course.
◊ Analog
◊ Digital
Thus, a signal is converted from analog to digital form by first discretizing the signal. This will
require the study of sampling theorem and techniques in this course.
• Channel:
Channel refers to the medium through which the information-bearing signal travels from the output of
the transmitter to the input of the receiver. The function of the channel is to provide connection
between the transmitter and the receiver. The channel can be
▪ Guided transmission channel e.g telephone lines, coaxial cables, fibre optics cables
▪ Free propagation channel e.g microwave link, radio wave links, free space optics,
• Noise/Interference
During the process of transmission and reception, the signal gets distorted due to noise in the system.
Noise
▪ could be internal or external to the system but the noise that has greatest effect on the signal is
an external noise within the channel.
• Receiver
The function of a receiver is to retrieve the transmitted signal and then process the signal to obtain
estimates of the transmitted information.
▪ Transmission power
▪ Channel bandwidth
◊ There is thus need for representation of the signal in the frequency domain
▪ Fourier series is a particular type of orthogonal series that is very useful in solving engineering
problems, especially communication problems. The orthogonal functions that are used are
either sinusoids or, equivalently, complex exponential functions.
▪ Fourier transform can be described as the method used for finding the frequencies of
waveform of any type
▪ Distortion means any change in a signal that alters the basic waveform or the relationship
between various frequency components and it usually leads to degradation of the signal.
▪ Group delay is the time delay of the amplitude envelopes of the various sinusoidal components
of a signal, and it is a function of frequency for each sinusoidal component.
• Another very important aspect of communication process is modulation of signal to be transmitted and
demodulation of the received signal. The design principles of a communication system deals with how
to efficiently use the available communication resources usually in a tradeoff manner.
Modulation is a process that causes a shift in the range of frequencies in a signal. Reasons for
employing modulation technique include:
▪ practical antenna length: in order to transmit a wave effectively, the length of the transmitting
antenna should be approximately equal to the wavelength of the wave;
▪ modulation helps in noise immunity and attenuation (depending on the physical transmission
medium);
▪ multiplexing: several modulated signal can be combined for their simultaneous or concurrent
transmission over the channel. The signals that occupy the same range of frequencies can be
separated at the receiver.
Source of Message signal Estimate of message signal User of
Information Information
… Receiver
…
Transmitter Receiver
Modulator Demodulator
Transmitter
Waveform
Received signal
Channel
Communication System
Modulation
▪ Continuous-wave (CW) modulation: A sinusoidal wave is used as the carrier. A parameter of the
sinusoidal carrier wave is varied continuously in accordance with the message signal. Parameters
that can be varied include:
▪ AM Systems
◊ Single Side Band (SSB) Modulation: In DSB-SC it is observed that there is symmetry in the side
band structure. So, even if one half is transmitted, the other half can be recovered at the
receiver. By doing so, the bandwidth and power of transmission is reduced by half. Depending
on which half of DSB-SC signal is transmitted, there are two types of SSB modulation
To overcome these drawbacks, VSB modulation is used. VSB can viewed as a compromise
between SSB and DSB-SC. Thus, in VSB
- one sideband is transmitted fully and a small part (vestige) of the other sideband is
transmitted alongside.
▪ Pulse modulation: The carrier consist of a sequence of periodic rectangular pulses. The following parameters
of the pulse are modified in accordance with the message signal:
▪ Digital Pulse Modulation: In digital pulse modulation, message signal is represented in a form that is discrete
in both amplitude and time.