Introduction to Communication Systems

Flexible · Affordable · Accessible
the people’s university
TEL 213/05
Telecommunication
Principle
Course Overview
Semester January 2012

Course Organization
Unit Title Weeks Assessment
1 Introduction to Communication Systems
3
2 Principles of Digital Communication
3
Assignment #1 -
15%
3 Radio frequency communication
systems, Microwave Devices and
Antennas
4
Assignment #2 -
15%
4 Fixed Line Telephony, and Satellite
Communication Systems 4
Assignment #3 –
20%
5 Computer Communication Networks &
Internet 4
TOTAL 18

Tutorial Classes Planning
• Tutorial 1
• – 2 hours classroom
• Tutorial 2 -2 hours classroom
• (TMA 1 submission)
• Tutorial 3 -2 hours classroom +3 Hours Lab
• (TMA 2 submission)
• Tutorial 4 – 2 hours classroom
(TMA 3 +Lab Report submission)
• Tutorial 5– 2 hours classroom

Overall Assessment
Type Marks Due Date
TMA 1 15% Tutorial 2
Lab 5% Tutorial 4
Final Examination 50% After week 19
100%

Tips for Effective Tutoring
• Punctuality and attire
• Telephone Tutoring
• Internet Support
• Encouraging students to ask questions
and get to know them

Self-Study
• Six to seven hours per week
– Averagely one hour a day
• Suggested weekly reading and
corresponding assignments
– Please follow strictly the Course Guide, Table 1.0

What to do when you have
problems?
• Contact your tutor immediately.
• Do not delay in seeking help
– if you straighten out a problem when you first identify
it as a problem, you’ll be able to understand the work
that comes later.
• It’s rather like getting back on the right path
after making a wrong turn.
– The longer you delay, the harder it is to get back
• Your tutor is there to help you to learn and to
avoid frustrations in your learning.

TEL 213/05 Telecommunication Principle
Tutorial 1
Semester January 2012
Writer:
Clarence Goh

Welcome to Telecommunication
Principle !
• Subject Code: TEL 213/05
• Class:
• Tutor Name: ABC
• Tutor Telephone: ABC
• Contact Hours: ABC

Welcome!
• Tutorial 1

Why are we learning this?
• Everything we have today is based on telecommunications
including:
– Cell Phones
– Television
– The internet
– Satellite

3 Main components of a
communication system
• Transmitter
• Receiver
• Transmission line
Can you identify which is which from the picture above?
Note: If the tin can acts as both a receiver and a transmitter, it is known as a transceiver

Simplex/Half Duplex/Full
Duplex
• The following is a discussion on the THREE main types of transmission
circuits (channels), simplex, half duplex and full duplex.
• Simplex
– Data in a simplex channel is always one way. Simplex channels are not
often used because it is not possible to send back error or control
signals to the transmit end. An example of a simplex channel in a
computer system is the interface between the keyboard and the
computer, in that key codes need only be sent one way from the
keyboard to the computer system.
• Half Duplex
– A half duplex channel can send and receive, but not at the same time. Its
like a one-lane bridge where two way traffic must give way in order to
cross. Only one end transmits at a time, the other end receives.
• Full Duplex
– Data can travel in both directions simultaneously. There is no need to
switch from transmit to receive mode like in half duplex. Its like a two
lane bridge on a two-lane highway.

Simplex System
Example: Radio

Half Duplex System
Example: Walkie-talkie

Full Duplex System
Example: Telephone

Definition
• Baseband signal – original unmodulated signals
• Broadband signals – modulated signals
• Modulation - is the process of having baseband
voice, video or digital signal modify another
higher-frequency signal, the carrier to enable
transmission at greater distance with less loss
• Multiplexing – Process of “queuing” up signals
for transmission.

Modulation
Why modulate?
1.Combines the signal with the carrier in a unique way.
2.Makes the signal less susceptible to noise.
3.Decreases the size of the antenna needed to transmit signals.
4.Increases the distance of transmission.

Modulation
• Modulation techniques are methods used to encode digital information in an
analogue world.
• There are three basic modulation techniques
– AM (amplitude modulation)
– FM (frequency modulation)
– PM (phase modulation)
• All 3 modulation techniques employ a carrier signal. A carrier signal is a
single frequency that is used to carry the intelligence (data).
– For digital, the intelligence is either a 1 or 0.
– When we modulate the carrier , we are changing its characteristics to
correspond to either a 1 or 0.

Modulation

Amplitude Modulation
• Modifies the amplitude of the carrier to represent 1s or 0s
– a 1 is represented by the presence of the carrier for a
predefined period of 3 cycles of carrier.
– Absence or no carrier indicates a 0
• Pros
– Simple to design and implement
• Cons
– Noise spikes on transmission medium interfere with the
carrier signal.
– Loss of connection is read as 0s.

Equations

AM and FM in TV
Transmission
• A terrestrial television signal is comprised of AM
and FM. AM is used for video while FM, for
video.
• Modulation is a process of combining a high
frequency, high amplitude signal (carrier) with an
information signal to enable the modulated
signal to be of high frequency, therefore
enabling long distance transmission (and
smaller antenna size)

AM Equations

Modulation Percentage
• M=Vm/Vc
• <1(undermodulation)
• =1 (100% modulation)
• >1 (overmodulation)

Amplitude modulated
waveform

Frequency Response of AM
signal

Frequency Response of AM
signal via Matlab Simulation

Power Equations for AM

Example 1 -AM Modulation Index and
modulation percentage
• Calculate the modulation index, m and percentage, M if the
modulation voltage is given as 3V, while the carrier voltage is 6V.
Conclude if the resultant modulated waveform is fully-modulated,
under-modulated or over-modulated.

AM Example 2
•Determine the total power, Pt
of the AM DSB system.
•What is the modulation factor, m?
•Calculate the upper sideband frequency and the lower sideband frequency.
•Calculate the bandwidth of this signal.

Solution – example 2 - AM

Example 3 - AM
• Calculate the modulation index, m if Vmax(p-p)
is 5.9V and Vmin(p-p) is 1.2V.

Frequency Modulation

FM equation and FM in
frequency spectrum

Finding bandwidth using
Bessel and Carson

Example - FM

Solution

Definition of Wavelength

Example - Wavelength
• Calculate the wavelength if the
frequencies of the following waves are
given as below:
• a. High-pitched sound wave (f=18kHz)
• b. Radio wave (f=10MHz)

Electromagnetic spectrum for
communication

Low Frequency usage
• Extremely Low Frequencies (ELF) are in the 30Hz -300Hz range. These include ac power line
frequencies (50 and 60Hz are common), as well as those frequencies in the low end of the
human audio range.
•
• Voice Frequencies (VF) are in the range of 300 to 3000Hz. This is the normal range of human
speech. Although human hearing extends from approximately 20 to 20000Hz, most intelligible
sounds occur in the VF range.
•
• Very Low Frequencies (VLF) are in the range of 9kHz to 30kHz and include the higher end of the
human hearing range up to about 15 to 20kHz. Many musical instruments make sounds in this
range as well as in the ELF and VF ranges. The VLF range is also used in some government and
military communication. For example, VLF radio transmission is used by the navy to
communicate with submarines.
•
• Low Frequencies (LF) are in the 30-300kHz range. The primary communication services using
this range are in aeronautical and marine navigation. Frequencies in this range are also used as
subcarriers, signals that are modulated by the baseband information. Usually, two or more
subcarriers are added, and the combination is used to modulate the final high-frequency carrier.

Medium to High Frequency
Usage
• Medium Frequencies (MF) are in the 300 to 3000kHz (0.3MHz-3.0MHz) range. The major
application of frequencies in this range is AM radio broadcasting (535 to 1605MHz). Other
applications in this range are various marine and aeronautical communication.
•
• High Frequencies (HF) are in the 3 MHz to 30MHz range. These are the frequencies generally
known as short waves. All kinds of simplex broadcasting and half-duplex two-way communication
take place in this range. Broadcasts from BBC occur in this range. Government and military
services use these frequencies for two-way communication. An example is diplomatic
communication between embassies. Amateur radio and citizens band (CB) communication also
occur in this part of the spectrum.
•
• Very High Frequencies (VHF) are in the 30MHz to 300MHz range. This popular frequency range
is used by many services, including mobile radio, marine and aeronautical communication, FM
radio broadcasting (88 to 108MHz) and TV channels (RTM channel 1, RTM channel 2 and
channel 8). Radio amateurs also have numerous bands in this frequency range.
•
• Ultra High Frequencies (UHF) are in the 300 MHz to 3000MHz range. This includes UHF TV
channels (such as TV3), and also for land mobile communication and services such as cellular
telephones as well as for military communication. Some radar and navigation services occupy
this portion of the frequency spectrum, and radio amateurs also have bands in this range.

Microwaves, EHF and optical
• Microwaves are in between 1000MHz (1GHz) and 30GHz. Microwave ovens
usually operate at 2.45GHz. Superhigh frequencies (SHFs) are in the 3GHz
to 30GHz range. These microwave frequencies are widely used for satellite
communication and radar. Wireless local-area networks (LANs) also occupy
this region.
•
• Extremely High Frequencies (EHF) are from 30GHz to 300GHz.
Electromagnetic signals with frequencies higher than 30GHz are referred to
as millimeter waves. Equipment used to generate and receive signals in this
range is extremely complex and expensive but there is a growing use of this
range for satellite communication and computer data.
•
• Frequencies between 300GHz and the Optical Spectrum. This portion of the
spectrum is rarely used. It is a cross between RF and optical. Lack of
hardware and components operating in this frequency range prevents its
use.

Telephone System

The television signal

AMPS Mobile Phone System

Problem with AMPS

New Mobile Telephone Switching Office
(MTSO) Systems

Multiple base stations
connected to MSC and PSTN

Example
• An area has 7 clusters and each cluster
has 7 cells. Calculate the number of RBS
and the number of cells in the area.
• Number of RBS = Number of clusters *
Number of cells = 7*7=49
• Number of cells= Number of RBS = 49

RBS, channels, cluster and cell

Conventional versus cellular
radio system
Conventional System Cellular Radio System
No frequency reuse Frequency reuse
Used before 1980's Used after 1980's
Low Capacity High frequency
Interference to adjacent space
areas
High capacity
High transmitted power No interference with adjacent
cells
High antenna height Low antenna height
Equipment bulky Hand Portable

Example
• Calculate the number of Erlangs if a user
were to remain in his/her cell, and makes
30 calls within an hour, with each call
lasting for a duration of 2 minutes.
• Minutes of traffic = number of calls *
duration
• =30*2=60
• Traffic Figure = 60/60=1 Erlang

Thank you!

Introduction to Communication Systems

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