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    CHAPTER 1

    EKT 231COMMUNICATION SYSTEM

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    LECTURERS

    1. Cik Aini Syuhada Md Zain

    [email protected]

    2. Soh Ping Jack

    [email protected]

    mailto:[email protected]:[email protected]:[email protected]:[email protected]
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    SYNOPSIS

    The aim of this subject is :to introduce the students with the basic principles and components ofcommunications system.

    This subject will cover various topics such as:

    Introduction to Communication System,

    Analogue Modulation and Demodulation (e.g. Amplitude Modulation),

    Angle Modulation (Frequency Modulation and Phase Modulation),

    Digital Modulation,

    Noise in Communication System, Transmission System and TransmissionLines.

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    Course Outcome (CO)PO1

    PO2

    PO3

    PO4

    PO5

    PO6

    PO7

    PO8

    PO9

    P

    O10

    P

    O11

    P

    O12

    Delivery Mode PossibleAssessment

    CO1:

    Understand basic principles

    of communication systems,

    and the essential of

    communication system in

    real world.

    3 1 1 3 1

    Lecture;

    Laboratory work;

    Tutorial;

    visiting lecturers

    Exams and/ortests;

    Lab report

    CO2:Ability to analyze noise and

    types of analog modulation

    and digital modulation and

    calculate SNR.

    2 2 3 3

    Lecture; Laboratorywork;

    Tutorial

    Exams and/ortests;

    CO3:Ability to properly use the

    laboratory equipments and

    instruments to measure and

    analyze output signals and

    performsome

    troubleshooting

    2 3 2 3 3

    Laboratory work Lab. Work;

    Lab. Report;

    CO4:Ability to apply related

    software tool in

    understanding principle of

    communication system.

    2 1 3 3

    Lecture;

    Lab Work;

    Discussion

    Lab. Work;

    Lab Report

    CO5:

    Ability to think logically,

    creatively and innovative,

    work in team and

    communicate effectively.

    3 2 2 3 2

    Laboratory work;

    Assignments

    Discussion;

    Oral discussion

    COURSE OUTCOMES (OBE)

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    REFERENCES

    Wayne Tomasi, Electronic CommunicationSystems Fundamentals Through Advanced 5th Ed,Prentice Hall, 2004.

    Paul Young, Electronics CommunicationsTechniques, 5thEdition, Prentice Hall, 2004.

    Mullet , Basic Telecommunications:The PhysicalLayer, Thomson Learning, 2003.

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    ASSESSMENT

    Final Exam = 50 %

    Coursework = 50 %

    Test x 2 = 15 %

    Lab Session = 20 %

    Lab Test = 10%

    Assignments/Quizzes = 5%

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    Signals and Systems Defined

    A signalis any physical phenomenon which

    conveys information

    Systemsrespond to signalsand produce new

    signals

    Excitationsignalsare applied at system

    inputsand responsesignalsare produced at

    systemoutputs

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    A Communication System as a

    System Example

    A communication systemhas an information

    signalplus noise signals

    This is an example of a systemthat consists of an

    interconnection of smaller systems

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    Signal Types

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    Conversions Between Signal Types

    Sampling

    Quantizing

    Encoding

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    Sound Recording System

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    Recorded Sound as a Signal Example

    s ign al

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    CHAPTER 1INTRODUCTION TO

    COMMUNICATION SYSTEM

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    Definitions

    Communications: Transfer of Information from one place to another.

    Should be efficient, reliable, and secured.

    Communication system: components/subsystems act together to accomplish

    information transfer/exchange

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    Definitions (Contd)

    Electronic communication system

    transmission, reception and processing ofinformation between two or more locations using

    electronic circuits. Information source

    analog/digital form

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    Think!

    Have you ever pictured yourself living

    in a world without any communication

    system?

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    Need For Communication

    Importance of communication:

    exchange of information between two partiesseparated in distances in a more faster andreliable way.

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    Information, message and signals

    InformationThe commodity produced by the source for transfer

    to some user at the destination.

    MessageThe physical manifestation of information as

    produced by the information source.

    SignalsA physical embodiment of informationvoltage

    signal or current signal

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    Brief History in Communication

    Year Events1844 Telegraph

    1876 Telephone

    1904 AM Radio

    1923 Television1936 FM Radio

    1962 Satellite

    1966 Optical links using laser and

    fiber optics1972 Cellular Telephone

    1989 Internet

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    Development and progress

    Communications between human beings

    Form of hand gestures and facial expressions

    Verbal grunts and groans

    Long distance communications

    Smoke signals

    Telegraph

    Telephone

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    Contd

    Wireless radio signals

    Triode vacuum tube

    Commercial radio broadcasting

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    Analog vs. Digital

    Analog

    Continuous Variation

    Assume the total range of frequencies/time

    All information is transmitted

    Digital

    Takes samples:

    non continuous stream of on/off pulses

    Translates to 1s and 0s

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    Analog vs. Digital

    Digital CSAdvantages:-Inexpensive-Privacy preserved(data

    encrypted)-Can merge different data-error correction

    Disadvantages:-Larger bandwidth-synchronization problem is

    relatively difficult

    Analog Cs

    Disadvantages:

    -expensive

    -No privacy preserved

    -Cannot merge different data

    -No error correction capability

    Advantages:

    -smaller bandwidth

    -synchronization problem isrelatively easier.

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    Basic Requirements of

    Communication System Rate of information transfer:

    how fast the information can be transferred

    Purity of signal received:whether the signal received is the same as the signal

    being transmit

    Simplicity of the system

    the simpler the system, the better Reliability

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    Elements of Communication

    System(CS)

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    Elements of CS(contd)

    Information

    The communication system exists to convey amessage.

    Message comes from information source

    Information forms - audio, video, text or data

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    contd

    Transmitter: Processes input signal to produce a transmitted signal

    that suited the characteristic of transmission channel.

    E.g. modulation, coding, mixing, translate

    Other functions performed - Amplification, filtering,antenna

    Message converted to into electrical signals by

    transducers E.g. speech waves are converted to voltage variation

    by a microphone

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    Elements of CS(contd)

    Channel (transmission media):

    a medium that bridges the distance from source todestination. Eg:Atmosphere (free space), coaxial

    cable, fiber optics, waveguide signals undergoes degradation from noise ,

    interference and distortion

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    Elements of CS(contd)

    Receiver:

    to recover the message signal contained in thereceived signal from the output of the channel, and

    convert it to a form suitable for the outputtransducer.

    E.g. mixing, demodulation, decoding

    Other functions performed: Amplification, filtering.Transducer converts the electrical signal at its input

    into a form desired by the system used

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    Modulation

    What is modulation? a process of changing one or more properties of the

    analog carrier in proportion to the information

    signal. One of the characteristics of the carrier signal is

    changed according to the variations of themodulating signal.

    AMamplitude, E FMfrequency ,

    PM - phase ,

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    Modulation (contd)

    Why modulation is needed?

    To generate a modulated signal suited andcompatible to the characteristics of the transmission

    channel. For ease radiation and reduction of antenna size

    Reduction of noise and interference

    Channel assignment Increase transmission speed

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    Noise, interference and distortion

    Noise

    unwanted signals that coincide with the desired signals.

    Two type of noise:internal and external noise.

    Internal noise Caused by internal devices/components in the circuits.

    External noise

    noise that is generated outside the circuit.

    E.g. atmospheric noise,solar noise, cosmic noise, man madenoise.

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    Noise, interference and distortion

    (Contd)

    Interference

    Contamination by extraneous signals from humansources.

    E.g. from other transmitters, power lines andmachineries.

    Occurs most often in radio systems whose receiving

    antennas usually intercept several signals at the sametime

    One type of noise.

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    Noise, interference and distortion

    (Contd)

    Distortion

    Signals or waves perturbation caused by imperfectresponse of the system to the desired signal itself.

    May be corrected or reduced with the help ofequalizers.

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    Limitations in communication

    systemTechnological problems

    Includes equipment availability, economic factors,federal regulations and interaction with existing

    systems. Problem solved in theory but perfect solutions may

    not be practical.

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    Limitations in communication

    system (contd)

    Physicals limitations

    Bandwidth limitation

    Measure of speed

    The system ability to follow signal variations depends onthe transmission bandwidth.

    Available bandwidth determines the maximum signalspeed.

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    Limitations in communication

    system (contd)

    Noise limitation

    Unavoidable.

    The kinetic theory.

    Noise relative to an information signal is measured interms of signal to noise ratio (SNR).

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    Communication system design

    Compromise within:

    Transmission time and power

    SNR performance

    Cost of equipments

    Channel capacity

    Bandwidth

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    FREQUENCY AND WAVELENGTH

    Cycle- One complete occurrence of arepeating wave (periodic signal) such as one

    positive and one negative alternation of a sine

    wave.Frequency- the number of cycles of a signal

    that occur in one second.

    Period - the time distance between two similar

    points on a periodic wave.Wavelength- the distance traveled by an

    electromagnetic (radio) wave during one

    period.

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    One cycle

    time

    PERIOD AND FREQUENCY

    COMPARED

    Frequency = f = 1/T

    T = One period

    F d l th d

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    +

    0 time

    distance

    Frequency and wavelength compared

    f = 1/T

    T

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    CALCULATING WAVELENGTH

    AND FREQUENCY

    = wavelength in meters

    f = frequency in MHz

    = 300/f

    f = 300/

    THE ELECTROMAGNETIC SPECTRUM

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    ELF

    103m

    107m

    104m

    105m

    106m

    10m

    1m

    10-1m

    10-2m

    10-3m

    10-4m

    102m

    300Hz

    30Hz

    30kHz

    3kHz

    300kHz

    30MHz

    3MHz

    300MHz

    3GHz

    300GHz

    30GHz

    THE ELECTROMAGNETIC SPECTRUM

    FROM 30 HZ TO 300 GHZ

    UHFVHFHFMFLFVLFVF SHF EHF

    Frequency

    Wavelength

    Millimeter

    waves

    ( = 300/f)

    (f = 300/)

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    LOW AND MEDIUM

    FREQUENCIES

    Extremely Low Frequencies - 30 to 300 Hz

    Voice Frequencies - 300 to 3000 Hz

    Very Low Frequencies - 3 kHz to 30 kHz

    Low Frequencies - 30 kHz to 300 kHz

    Medium Frequencies - 300 kHz to 3 MHz

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    HIGH FREQUENCIES

    High Frequencies- 3 MHz to 30 MHz

    Very High Frequencies- 30 MHz to 300 MHz

    Ultra High Frequencies

    - 300 MHz to 3 GHz

    (1 GHz and above = microwaves)

    Super High Frequencies- 3 GHz to 30 GHz

    Extremely High Frequencies

    - 30 GHz to 300 GHz

    THE ELECTROMAGNETIC

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    10-3m

    10-4m

    300GHz

    Millimeter

    waves

    THE ELECTROMAGNETIC

    SPECTRUM ABOVE 300 GHZ

    Wavelength

    0.8x10-6m

    0.4x10-6m

    Infrared

    V

    isible

    Ultraviolet

    X-rays

    Gam

    marays

    Cos

    micrays

    10-5m

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    OPTICAL FREQUENCIES

    Infrared - 0.7 to 10 micron

    Visible light - 0.4 to 0.8 micron

    Ultraviolet - Shorter than 0.4 micron

    Note: A micron is one millionth of a meter.

    Light waves are measured and expressed

    in wavelength rather than frequency.

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    TYPES OF COMMUNICATIONS

    TX RX

    TX

    TX

    RX

    RX

    Simplex:

    One-way

    Duplex:

    Two-way

    Half duplex:

    Alternate TX/RX

    Full duplex:

    Simultaneous

    TX/RX

    Channel

    Channel(s)

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    COMMUNICATIONS SIGNAL

    VARIATIONSBaseband- The original information

    signal such as audio, video, or computer

    data. Can be analog or digital.

    Broadband- The baseband signal

    modulates or modifies a carrier signal,

    which is usually a sine wave at afrequency much higher than the

    baseband signal.

    V i f f i ti

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    Various forms of communication

    system Broadcast: radio and television

    Mobile communications

    Fixed communication system- land line

    Data communication-internet

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    Frequency Spectrum &Bandwidth

    The frequency spectrum of a waveform consistsof all frequencies contained in the waveform andtheir amplitudes plotted in the frequency

    domain.The bandwidth of a frequency spectrum is the

    range of of frequencies contained in the

    spectrum.It is calculated by subtracting thelowest frequency from the highest.

    F S &B d id h

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    Frequency Spectrum &Bandwidth

    (contd)

    Bandwidth of the information signal equals tothe difference between the highest and lowestfrequency contained in the signal.

    Similarly, bandwidth of communication channelis the difference between the highest and lowestfrequency that the channel allow to pass through

    it

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    Power gain

    Signal level gain

    signal gain

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    signal gain

    In Engineering Problems, we have known the termsignal gain / mechanical advantage;

    Examples are chain pulley block, cantilever, gear,amplifier, transformer.

    Voltage amplifier: Av= Vo/Vi.Transistors current gain: = ic/ib,

    Chain pulley block: weight lifted/weight applied.

    Transformer: secondary voltage/primary voltage gear box: output torque/input torque.

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    Power gain

    It is the ratio of output power over input power.

    Ap= Po/Pi.

    If the energy is consumed in doing a work, Power gainis always1.

    Example is transformer, chain pulley block, gearboxes etc have power gain less than one.

    In amplifiers, the apparent power gain may be more

    than one. The signal power is amplified. DC electricpower is transformed into signal power.

    In signal gain:

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    In signal gain:

    The advantage or, signal gain may be >1 though the

    power gain is < 1.

    At first instance, it appears that there is no apparentrelation between signal gain and power gain.

    It is because the friction of the load in which thepower is fed, is not accounted.

    P r nd lt in in

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    Power and voltage gain in

    communication

    In communication, due to known characteristicimpedance of the channel, the power andvoltage gains become explicit.

    It is designated in terms of decibels, dB.

    Power gain in dB = 10 log (Po/Pi) dB.

    Voltage gain in dB = 20 log (Vo/Vi) dB.Here if power gain < 1, voltage gain

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    power ratio Po/Pi = 10,000 = 40 dB

    Voltage ratio Vo/Vi = 100 = 40 dB.

    See that Po/Pi = (Vo/Vi)2

    (Po/Pi)dB = 2(Vo/Vi)dB

    g g ( o i)

    Voltage gain in dB = 20 log (Vo/Vi) dB.

    are absolute gains

    Term is power

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    Alternatively:

    Power gain = 10(gain in dB/10)

    Voltage gain = 10 (gain in dB/20)

    Examples:

    A 64 dB gain means 106.4= 2.5212x106watts.

    An attenuation by 0.01= 10 log(0.01)

    = -20 dB

    E l

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    Examples:

    Let there be two amplifiers in cascade. Theirgains are 13 dB and 10 dB respectively.

    The overall gain is 13+10 = 23 dB.

    In terms of ratio:

    23 dB = 10(23/10)= 200

    13 dB = 10(13/10)= 20

    10 dB = 10(10/10)

    = 10Again 20 x 10 = 200.

    same

    Sum

    multiplication

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    Relative dB

    It is convenient to express signals with somereferencesuch as

    1mW power or,

    1 V voltage level.

    This permits input- and output- signals to beexpressed in terms of relativedB.

    When referenced to 1mW, it is written dBm

    When referenced to 1 V, it is written as dBV

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    Relative dB is not a gain

    but is termed as gain wrt a reference.

    5 watts signal,

    In relative dB; 10 log(5W/1mW) = 36.99 dBm

    500 V signal:

    In relative dB; 20 log(500 V /1 V ) = 53.98dB

    V