Introduction to Communication Systems

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TEL 213/05 Telecommunication

Principle

Course OverviewSemester January 2012



Course Organization

Unit Title Weeks Assessment

1 Introduction to Communication Systems 3

2 Principles of Digital Communication3

Assignment #1 -

15%

3 Radio frequency communication systems, Microwave Devices and Antennas

4Assignment #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 1Semester 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.



Amplitude Modulation



Amplitude Modulation 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 SystemNo frequency reuse Frequency reuseUsed before 1980's Used after 1980'sLow Capacity High frequencyInterference to adjacent space areas

High capacity

High transmitted power No interference with adjacent cells

High antenna height Low antenna heightEquipment 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

Engineering

Transcript of Introduction to Communication Systems