COMM704- Introduction.pdf

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Winter 2008 1

COMM 704: Communication Systems

Lecture 1:

Introduction

Associate Prof. Dr. Soliman MahmoudFaculty of Information Engineering and Technology

Electrical and Electronic Department

[email protected]

Associate Prof. Dr. Soliman Mahmoud

Electronics and Electrical Engineering Department

COMM 704, Communication Systems

Winter 2008 2

Instructor : Associate Prof. Dr. Soliman MahmoudOffice : C3-320Office Hours :Tuesday, 9:00- 12:00TA : Eng. Eman Azab and Eng. Ahmed Bahaa

Course Team

Course Component

1 lectures per week and 1 tutorials per week

10%Project

Course Assessment


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Motivation for Communication System Course

Many courses in communications traditionally focus onclassical communication theorywith little attention given toactual implementation aspects of analog or digital systems.For the most part, the hardware implementation ispredisposed to the electronics curriculum. Thecommunication systems course (COMM 704) is a newcourse for communication students in the faculty of IET. Inthis course the theoretical aspects of communicationssystems are combined with integrated circuitimplementation, make the theory of communications

systems come to real life using a design, build, and testprocess.




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Course Description

This course introduces the fundamentals of electroniccommunication systems. Topics include AM/FM/TV radiosystems, digital and spread spectrum communicationsystems, with strong emphasis on electronic circuits usedin these communications systems. Upon completion,students should be able to interpret analog and digital

communication circuit diagrams, analyze transmitter andreceiver circuits, and use appropriate communication testequipment.


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Electronic Communication Systems:

I. AM Radio Systems

II. FM Radio Systems

III. TV Radio Systems

IV. Digital Modulation systems

V. Spread SpectrumCommunication systems

Electronic Communication Circuits:

I. Multipliers, Phase detectorsand

AM modulators

II. Oscillators

III. Filters and Tuned Circuits

IV. Phase Locked Loop (PLL),Frequency synthesizers,

Frequency dividers

V. Power Amplifiers

Course Outline




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Course Outline


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References

1. Frank R. Dungan, Electronic Communications Systems, ISBN 0-534-07698-X,PWS Publishers.

2. William Schweber, Electronic Communications Systems: A complete Course,Prentice-Hall, Englewood Cliffs, ISBN 0135900921.

3. Robert Dixon, Radio Receiver Design, Marcel Dekker, Inc., ISBN 0-8247-14448-0161-5.

4. Ramesh Harjani, Design of High-Speed Communication Circuits (Selectedtopics in Electronics and Systems), ISBN: 9812565906.

5. Robert Kellejan, Applied electronic communication : circuits, systems,transmission ISBN: 0574215352 : 9780574215352.

6. J.R. Smith, Modern Communication Circuits, 2nd Edition, McGraw-Hill, NewYork, 1986.

7. Ray Black Comprehensive Electronic Communication, West Publishing(1997)

Textbook and References

Prerequisites

Communication Microelectronics (ELCT 508), Linear time-invariant Signalsand Systems (COMM 401), Modulation I (COMM 601) and Modulation II(702).

Winter 2008 8

COMM 704: Communication Systems

Lecture 1:

Revisions of AM/FM Radio Systems


Faculty of Information Engineering and Technology

Electrical and Electronic Department

[email protected]


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Winter 2008 9

AM/FM Radio Systems

Objectives and outline:

1. Principles of radio transmission

2. AM Transmitter

3. FM Transmitter

4. AM and FM radio frequencies

5. AM Superhetrodyne Radio Receiver6. FM Superhetrodyne Radio Receiver

7. 3 band, GSM/GPRS Transceiver




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1. Principles of radio transmission

Transfer of information (speech, music, image, computer data etc.) byradio can be presented in its simplest form with block - diagram as shownin Fig.1.

Fig.1 Radio Transmission Block diagram


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2. AM Transmitter Block diagram of a simple AM signal transmitter is shown in Fig.2. Theamplitude modulation is being performed in the modulator. Two signalsare entering it: HF signal called the carrier (or the signal carrier), being

created into the HF oscillator and amplified in the HF amplifier to therequired signal level, and the LF (modulating) signal coming from the

microphone or some other LF signal source (cassette player, recordplayer, CD player etc.), being amplified in the LF amplifier. Onmodulator's output the amplitude modulated signal xAM (t) is acquired.

This signal is then amplified in the power amplifier, and then led to the

emission antenna.

Fig.2 AM Transmitter Block diagram

To implement this simple AM

transmitter; we need to thefollowing electronic circuits:

1. Small Signal Amplifiers (LFand HF Amplifiers)

2. Large Signal Amplifiers

(Power Amplifiers)

3. Oscillators (Square-

Triangular- Sinusoidal)

4. AM Modulator ( Multiplier andadder)




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3. FM Transmitter

Block diagram of an FM transmitter is shown in Fig.3. The modulating signal, is a signal from some LF source.it is being amplified in LF amplifier and then led into the HF voltage controlled oscillator, where the carriersignal is being created. The carrier is a HF voltage of constant amplitude, whose frequency is, in the absence

of modulating signal, equal to the transmitter's carrier frequency fC. In the oscillatory circuit of the HF VCO a

varicap (capacitive) diode is located. It is a diode whose capacitance depends upon the voltage between itsends, so when being exposed to LF voltage, its capacitance is changing in accordance with this voltage. Dueto that frequency of the oscillator is also changing, i.e. the frequency modulation is being obtained. The FM

signal from the HF oscillator is being proceeded to the power amplifier that provides the necessary outputpower of the transmission signal.

Fig.3 FM Transmitter Block diagram

To implement this simple FMtransmitter; we need to the

following electronic circuits:

1. Small Signal Amplifiers (LF

and HF Amplifiers)

2. Large Signal Amplifiers

(Power Amplifiers)

3. Voltage controlled Oscillator


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4. AM and FM radio frequencies

The AM radio carrier frequencies are in the frequency

range 535-1605 kHz. Carrier frequencies of 540 to 1600kHz are assigned at 10 kHz intervals.

The FM radio band is from 88 to108 MHz between VHF televisionChannels 6 and 7. The FM stationsare assigned center frequencies at200 kHz separation starting at 88.1

MHz, for a maximum of 100stations. These FM stations have a75 kHz maximum deviation from thecenter frequency, which leaves 25kHz upper and lower "gaurd bands"

to minimize interaction with theadjacent frequency band.

The different radio stations sharethe frequency spectrum over the airthrough AM and FM modulation.

Sharing the AM/FM radio spectrumis achieved through FrequencyDivision Multiplexing (FDM).

Different audio sources have different bandwidth W: Speech- 4kHz, High quality music-15kHz. AM radio limits baseband bandwidth W=5kHz. FM radio uses baseband bandwidthW=15kHz.

Transmission bandwidth BT is the bandwidth occupied by a message signal in the radiofrequency spectrum. For AM : BT=2W , for FM BT 2W (1+); Carson Rule.




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AM Radio Spectrum

FM Radio Spectrum


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Cf

IFCLO fff +=

IFf mf mf mf

KHzfIF

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5. AM Superhetrodyne Receiver

Fig.4 AM Superhetrodyne Rx.

Requirements from Radio

receivers:Tune to and amplify

desired radio stationFilter out all other stationsDemodulator has to workwith all radio stationsregardless of carrier

frequency.

For the demodulator towork with any radio signal,we convert the carrierfrequency of any radiosignal fC to Intermediate

Frequency (fIF). Radio receiver design can

be optimized for thatfrequencySuperhetrodyne RX

RF Filter: Radio Frequency filter select the desired channel (fC) and reject the image channel(fC+2fIF). 2W < BW RF


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7. 3 band, GSM/GPRS Transceiver

Global System for Mobile communications (GSM) General Packet Radio Service (GPRS)

COMM704- Introduction.pdf

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