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    Page 1Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    Communication Systems Seminar

    Lecture 3

    Modulation and Demodulation

    Techniques in Communication Systems

    Dr. Oke C. Ugweje

    Department of Electrical & Computer Engineering

    The University of Akron

    Akron, OH 44325-3904

    Wednesday June 28, 2000

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    Page 2Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    Outline of Presentation

    FModulation and Demodulation (MODEM)

    FClassification of Modulation Techniques

    FBaseband versus Bandpass Communications

    FWhy Modulate?

    FDefinition of Modulation

    FAnalog Modulation Techniques

    FDigital Modulation Techniques (Sample)

    FDetection Detection Techniques

    FDigital MODEM Examples

    mASK, FSK, PSK, QPSK, OQPSK, DPSK, QAM

    F Factors Affecting Choice of Modulation

    FComparisons of Digital MODEM

    FReferences

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    Page 3Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    Modulation and Demodulation (MODEM)

    Format MultiplexChannel

    Encoder

    Source

    EncoderSpread

    Format DemultiplexChannelDecoder

    SourceDecoder

    Despread

    Bits or

    Symbol

    To otherdestinations

    From other

    sourcesDigitalinput

    Digital

    outputSource

    bits

    Sourcebits

    Channelbits

    Carrier & symbolsynchronization

    Channelbits

    $mil q

    mil q MultipleAccess

    Waveforms

    MultipleAccess

    Tx

    Rx

    PerformanceMeasure

    $Pe

    Modulate

    Demodulate&Detect

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    Page 4Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    Classification of Modulation Techniques

    mModulation Techniques can be broadly classified as follows:lDigital versus Analog Modulation

    lBaseband versus Bandpass (Passband) Modulation

    lBinary versus M-ary Modulation

    lMemoryless Modulation versus Modulation with memory

    l Linear versus Nonlinear Modulation

    lConstant envelope versus Non-constant envelope Modulation

    l Power efficient versus Bandwidth efficient Modulation

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    Page 5Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    Baseband versus Bandpass Communications

    mBaseband (Lowpass):lA signal whose frequency content (i.e. its spectrum) is in the

    vicinity of zero (i.e.,f = 0 or dc) is said to be a baseband signal

    wOriginal source signal are sometimes said to be baseband

    lBaseband systems transmit baseband signals

    l This is usually not an effective means of communication. Why?

    mBandpass (Passband or Narrowband):

    lBandpass signal spectrum is nonzero in some band of frequency

    with BW = 2B centered aboutf = fc, wherefc >> 0

    mEffective transmission of signal usually requires bandpass signal

    X(f)

    -B2-B1 -fc 0B2B1 ffc

    X(fc)

    2B2B

    fc is carrier frequency

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    Page 6Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    mBandpass transmission involves some translation of the basebandsignal to some band of frequency centered aroundfc

    mBandpass Transmitter:

    lCarrier (high frequency pure sinusoidal generated by the local

    oscillator) is altered in response to a given low frequency signal

    (message signal) generated by the source

    ModulatorFrequency

    Translation

    Power

    Amplifier

    LocalOscillator

    Source

    MessageSignal

    RF CarrierModulatedCarrier

    Carrier for

    ModulationCarrier for

    TranslationWire

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    Page 7Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    Why Modulate?

    mCoupling EM wave into space - antenna size wavelength

    l For speech signalf = 3 kHz = 105m

    lAntenna size without modulation = 105m = 60 miles

    l Practically unrealizable

    lHence, efficient antenna of realistic physical size is needed for

    radio communication system

    m Information signal must conform to the limitation of its channel

    (channel matching)mReduce the effect of interference, e.g. Spread Spectrum

    m Place signals at desired frequency band for signal processing purposes

    such as filtering, amplification, multiplexing

    mUsed to map digital information sequence into waveforms

    = cf

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    Page 8Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    Definition of Modulation

    mThe technique of superimposing the message signalon the carrierisknown as modulation

    mThat is, modulation is the process by which a property or parameter of

    one signal (in this case the carrier) is varied in proportion to the

    second signal (in this case the message signal)

    mModulation is performed at the transmitter, and the reverse operation(demodulation/detection) is performed at the receiving end

    mLet m(t) = message (or information) signal

    c(t) = carrier signal

    s(t) = modulated signal (transmitted signal)

    Modulatorm(t) s(t)

    c(t)

    Modulating

    Carrier

    Modulated

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    Page 9Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    lThe carrierc(t) is a pure sinusoidal signal generally given as

    whereAc = Amplitude,fc= Frequency, c(t) = Phase

    l Examination ofc(t) indicate that there are 3 parameters which may

    be varied:

    1. The amplitudeAc,

    2. Thefrequencyfc, and

    3. Thephase c(t)

    l These parameters can be varied in Analog or Digital form

    lWhen varied in Digital form, it is referred to as Shifting &

    Keying

    c t Ac

    fct

    ct( ) cos( ( ))= +2

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    Page 10Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    Analog Modulation Techniques

    mUsing the message signal m(t) to varyAc,fc, c(t) leads to 3 basictypes of analog modulation schemes respectively known as

    1. Amplitude Modulation

    2. Frequency Modulation and

    3. Phase Modulation

    mThese types of modulation are carrier/continuous wave modulation

    m In this case, theIntermediate Frequency (IF) or theRadio

    Frequency (RF) is modulated

    m Frequency & Phase Modulation are also known asAngle ModulationmAmplitude Modulation (AM) is used whenever a shift in the

    frequency components of a given signal is desired

    l E.g., transmitting voice signal (3 kHz) via EM wave requires that

    3 kHz be raised several orders of magnitude before transmission

    AmplitudeModulator

    m(t) s(t)

    c(t)

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    Page 11Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    m There are 4 kinds of Amplitude Modulation techniques, namely:

    1) Conventional Amplitude Modulation

    Carrier + Upper Sideband + Lower Sideband

    2) Double Sideband (DSB) Suppressed Carrier (SC) AM

    Upper Sideband + Lower Sideband

    3) Single Sideband (SSB) AM

    Only one Sideband (Upper Sideband or Lower Sideband)

    4) Vestigial Sideband (VSB) AM

    Upper Sideband + portions of the Lower Sideband

    fm fm0

    M f( )

    fc fm +fc fmfc fc fm fc fm+fc

    M f fc( )

    USBUSB

    M f fc( )+

    aAc2

    S fam

    ( )

    M( )0

    LSB LSB

    f

    f

    Ac2

    Ac2

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    Page 12Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    Digital Modulation Techniques (Sample)

    FThe purpose of digital modulation is to convert an information-bearing discrete-time symbol into a continuous-time waveform

    FBasic Techniques (Binary, M = 2):

    mCommon binary modulation schemes include

    lAmplitude Shift Keying (BASK)

    lFrequency Shift Keying (BFSK)

    lPhase Shift Keying (BPSK)

    lDifferential Phase Shift Keying (DPSK)

    FFor M > 2, many variations of the above techniques exist usually

    classified as M-ary modulation

    mM-ary modulation schemes include

    lPhase Shift Keying (MPSK)

    w Quadrature Phase Shift Keying (QPSK)

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    Page 13Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    w Offset QPSK (Staggered QPSK) (OQPSK/SQPSK)

    w /4 Differential QPSK (no carrier) (/4 DQPSK)

    w /4 Differential QPSK (with carrier) (/4 QPSK)

    w Differential MPSK (no carrier recovery) (DMPSK)

    lContinuous-Phase Frequency Shift Keying (CPFSK)

    lSinusoidal Frequency Shift Keying (SFSK)

    lMinimum Shift Keying (MSK)

    w Differential MSK (DMSK)

    w Gaussian MSK (GMSK)

    lAmplitude Phase Keying (MAPK)

    lQuadrature Amplitude Modulation (MQAM)

    w Superposed QAM

    lQuadrature Partial Response Signaling (QPRS)

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    Page 14Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    Digital Detection Techniques

    MODEM

    NONCOHERENTCOHERENT

    BINARY M-ary HYBRID BINARY M-ary HYBRID

    ASK(OOK)

    FSK

    (MSK)

    PSK

    ASK

    FSK

    PSK(QPSK,OQPSK)

    APK(QAM) ASK

    FSK

    DPSK

    CPM

    ASK(OOK)

    FSK

    DPSK

    CPM

    (Phase inforequired)

    (No Phase inforequired)

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    Page 15Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    Digital MODEM Examples

    FAmplitude Shift Keying (ASK)

    mModulation Process:

    wAmplitude of the carrier is switched between two (or more)

    levels according to the digital data

    xm t( )

    A tocos( )

    s t( )

    Baseband Data Modulated bandpass SignalOOK Modulator

    Product modulator or

    ON-OFF switch

    0 T 3T

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    Page 16Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    mDetectors for ASK:

    mPower Spectral Density:

    2Tb f Rc b+

    f Rc b

    + 2

    impulse

    B RT

    bb

    = =2 2

    l Bandwidth

    w Null-to-null bandwidth

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    Page 17Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    Frequency Shift Keying (FSK)

    mModulation Process:

    l InFSK, the instantaneous frequency of the carrier is switched

    between 2 or more levels according to the baseband digital data

    mWaveform:

    mDiscontinuous Phase FSK:

    f1

    f2

    s t A t o c( ) cos( )= + 1 1 s t A t c1 2 2( ) cos( )= +

    1 2 Phase Discontinuities

    1 1 1 100

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    Page 18Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    mContinuous Phase FSK:

    mDemodulation of FSK:

    No Phase Discontinuities

    1 1 1 100

    0 1=

    Coherent Noncoherent

    Envelop

    Detection

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    Page 19Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    mPSD of CPFSK:

    Sunde's FSK

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    Page 20Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    Phase Shift Keying (PSK)

    mModulation Process:

    l InPSK, the phase of the carrier signal is switched between 2 or

    more values in response to the baseband digital data

    mWaveform:

    mPSK Generation:

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    Page 21Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    mReceiver (Demodulator) for PSK:

    ?There is no non-coherent detection equivalent for PSK. Why?

    mPower Spectral Density of PSK:

    l Similar to that of ASK

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    Page 22Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    Quadrature PSK

    E

    10

    01

    11

    00

    s0s

    1

    s2

    s3

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    Page 23Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    m In QPSK, the bit transition in I- & Q-channels occur simultaneously

    Simultaneous

    transition of Qand I channels

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    Page 24Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    Offset QPSK

    m In OQPSK, I-channel (or Q-channel) bit stream is offset by one bit

    period w.r.t. the Q-channel (or I-channel) prior to multiplication by

    the carrierNotice that the Q and I channels are

    not aligned and only one phase

    transition can occur once every Ts =

    Tb sec with a max at 90o

    I-channel: even bits

    Q-channel: odd bitsPhase Diagrams

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    Page 25Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    Differential PSK (DPSK)

    mDPSK is regarded as the noncoherent version of binary PSK

    DelayTs

    dk

    dk1

    dd a

    d akk k

    k k

    ===

    RST

    1

    1

    0

    1

    ,

    ,ak ak dk dk1

    0 0 1

    0 1 0

    1 0 0

    1 1 1

    M_ary Case

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    Page 26Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    Quadrature Amplitude Modulation (QAM)

    mMost commonly used combination ofamplitude andphase signaling

    is the Quadrature Amplitude Modulation (QAM)

    mMQAM Modulator:

    mM-ary QAM Demodulation:

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    Page 27Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    mQAM Constellation:Q

    II I

    QQ

    Type I Type II Type III

    16 QAM (8, 8) 16 QAM (4, 12) 16 QAM (4, 8, 4)

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    Page 28Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    Factors Affecting Choice of Modulation

    m Signal-to-noise ratio (SNR)

    m Probability of error or Bit Error Rate (BER)

    m Power Efficiency, p

    l Power efficiency is a measure of how much received power is

    needed to achieve a specified BER (inversely proportional to BER

    lAs BER increases, p decreases since transmitted power is

    wasted on more bad data

    mBandwidth Efficiency (or Spectral Efficiency), B

    lDefined as the ratio of the bit rate to the channel bandwidth

    w IfR is data rate and B is the RF signal bandwidth, then

    wThe capacity of a digital system is directly related to B

    BR

    B BT M bps Hz = =

    12log /

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    Page 29Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    wThe max possible bandwidth efficiency is

    ?Note: Binary systems are more Power Efficient, but less Spectral

    Efficient than M-ary systems

    m Performance in multipath environment

    l Envelope fluctuations and channel non-linearity

    m Implementation cost and complexity

    ?No modulation scheme possesses all the above characteristics; hence,

    trade-off are made when selecting modulation/demodulation schemes

    BC

    B

    S

    Nbps Hz

    maxlog / = = +FH

    IK2 1

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    Page 30Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    m For example, in wireless communications, it is important to select

    MODEM based on the following requirements

    lHigh Spectral Efficiency

    lHigh Power Efficiency

    lHigh Fading Immunity

    FPractical Modulation Schemes

    mFM AMPS

    mMSK CT2

    mGMSK GSM, DCS 1800, CT3, DECT

    mQPSK NADC (CDMA) - base transmitter

    mOQPSK NADC (CDMA) - mobile transmitter

    m4-DQPSK NADC (TDMA), PDC (Japan), PHP (Japan)

    mMPSK (some wireless LANs)

    w These factors are affected

    by baseband pulse shape

    and phase transition

    characteristics of the signal

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    Page 32Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    Error Performance Comparison

    Modulation Type PM(coherent) P b (coherent) P b (noncoherent)

    m Baseband Systems

    l Unipolar

    l Polar

    l Bipolar

    m Bandpass Systems

    l BASK (OOK)

    l BFSK

    l BPSK

    l QPSK

    l OQPSK

    l DPSK

    QEsNo

    e j

    QEbN

    2

    0e j

    QEb

    N

    2

    0e j

    12

    2

    8exp ANo

    e j

    12 2exp

    Eb

    Noe j

    QEbN0

    e j

    32

    0

    QEbNe j

    QEbN0

    e j

    QEbN0

    e j

    QEbN0

    e j

    22

    0

    QEs

    Ne j

    12 exp

    EbN

    o

    e j

    22

    0

    QEs

    N Msine j

    Requires coherent detection

    QEb

    N

    2

    0e j Requires coherent detection

    QEsN0

    e j

    QEs

    No

    2e j

    Not used in practice

    22

    12

    0 0Q

    EN Q

    EN

    b bFHIK

    FH

    IK

    L

    NM

    O

    QP

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    Page 33Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    mError Performance of BPSK/QPSK:

    P QE

    NQ

    A T

    Nb

    b

    o

    b

    o

    =FHG

    IKJ

    FHG

    IKJ

    22

    2

    2

    P QE

    Nerfc

    E

    Ne

    b

    o

    b

    o

    =FHG

    IKJ

    =FHG

    IKJ

    22 1

    2

    Bit Error Rate

    Symbol Error Rate

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    Page 34Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    mError Performance of BPSK/QPSK/DPSK/DQPSK/MQAM:

    P M QME

    EsNo

    ( ) sin FHIK2

    2

    Bit/Symbol Error Rate

    Symbol Error Rate

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    Page 35Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    mOther Performance Comparison

    24.3 dB40.33Rb18.3 dB16-PSK

    18.8 dB30.33Rb14.0 dB8-PSK

    13.6 dB20.5Rb10.6 dBQPSK

    10.6 dB1Rb10.6 dBBPSK

    Required

    CNR

    Max B(bits/s/Hz)

    Min Channel B for

    ISI free signaling

    Required

    Eb/No

    Modulation

    SchemePb = 10

    -6

    Null-to-Null

    2/3

    1.0

    1.0

    0.5

    Bandwidth Efficiency, B

    d (complex)A (best)N/A9.6 dBMSK

    cB2.09.6 dBOQPSK

    aC2.09.6 dBQPSK

    a (simple)D (worst)1.09.6 dBBPSK

    Implementation

    Complexity

    Immunity to

    NonlinearityNyquist

    Eb/No

    (dB)

    Modulation

    Scheme

    Pb = 10-5

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    Page 36Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    mComplexity

    Complexity High

    APK

    M-ary PSKQPR

    CPFSK - optimal detection

    MSK

    OQPSK

    QAM, QPSK

    BPSK

    Low

    OOK - envelope detection

    DQPSK

    DPSK

    CPFSK -discriminator detection

    FSK - noncoherent detection

    Ref: IEEE Communications Magazine 1988?

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    Page 37Communication Systems Seminar, Summer 2000

    Glenn Research Center University of Akron

    Modulation and Demodulation

    References

    1. O. C. Ugweje, Class Handouts on Communications and Signal Processing, Digital

    Communications, Wireless Communications, University of Akron, Akron Ohiohttp://www.ecgf.uakron.edu/ugweje/web/home.html

    2. B. Sklar,Digital Communications Fundamentals and Application, Prentice-Hall,

    Englewood Cliffs, NJ, 1988.

    3. A. Bateman,Digital Communications Design for the Real World, Addison-

    Wesley, 19884. J. G. Proakis,Digital Communications, 3rd Edition, McGraw-Hill, 1994.

    5. J. G. Proakis and Masoud Salehi, Communication Systems Engineering, Prentice-

    Hall, 1994

    6. A. Ambardar,Analog and Digital Signal Processing, PWS Publishing Company,

    MA, 19957. K. Feher, Digital Communications: Satellite/Earth Station Engineering,

    Prentice-Hall, Inc., New Jersey, 1983