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    NCCUWireless Comm. Lab.

    Chapter 5Effect of Noise on Analog Communication

    Systems

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    Outline)Chapter 5 Effect of Noise on Analog Communication Systems

    A5.1 Effect of Noise on linear-Modulation Systems

    5.1.1 Effect of noise on a baseband system5.1.2 Effect of noise on DSB-SC AM

    5.1.3 Effect of noise on SSB AM

    5.1.4 Effect of noise on conventional

    A5.2 Carrier-Phase Estimation with a phase-Locked Loop (PLL)

    5.2.1 The phase-locked loop (PLL)

    5.2.2 Effect of additive noise on phase estimation

    A5.3 Effect of noise on angle modulation5..3.1 Threshold effect in angle modulation

    5.3.2 Pre-emphasis and De-emphasis filtering

    A5.4 Comparison of analog-modulation systems

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    OutlineA5.5 Effects of transmission losses and noise in analog

    communication systems

    5.5.1 Characterization of thermal noise sources

    5.5.2 Effective noise temperature and noise figure

    5.5.3 Transmission losses

    5.5.4 Repeaters for signal transmission

    A5.6 Further reading

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    5 Effect of Noise on Analog Communication Systems

    )The effect of noise on various analog communication systemswill be analysis in this chapter.

    )Angle-modulation systems and particularly FM, can providea high degree of noise immunity, and therefore are desirablein cases of severe noise and/or low signal power.

    )The noise immunity is obtained at the price of sacrificingchannel bandwidth because he bandwidth requirements ofangle-modulation systems is considerably higher thanamplitude-modulation systems.

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    -W W

    LPT

    Nu(t) r(t)

    m(t)

    5.1 Effect of Noise on linear-Modulation Systems

    (1) Baseband system) (1) Baseband system

    ( ) 02

    n

    NS f =

    0

    00

    2

    w

    nw

    NP df N W

    +

    = =:RP received power

    0 0

    R R

    b N

    S P PThen

    N P N W

    = =

    baseband

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    m(t) DSB-SCDemodulation

    Nu(t)

    r(t)

    DSB-SCmodulation

    5.1 Effect of Noise on linear-Modulation Systems

    (2) DSB-SC AM) (2) DSB-SC AM

    ( ) ( ) ( )cos 2c c cu t A m t f t = +

    ( ) ( ) ( )( ) ( )

    ( ) ( ) ( ) ( )

    cos 2

    cos 2 sin 2

    c c c

    c c s c

    r t u t n tA m t f t

    n t f t n t f t

    = += +

    +

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    5.1 Effect of Noise on linear-Modulation Systems

    (2) DSB-SC AM)Coherent demodulation

    ( ) ( )

    ( ) ( ) ( )

    ( ) ( ) ( )

    ( ) ( ) ( )

    ( ) ( ) ( ) ( ) ( )

    ( ) ( )

    ( ) ( )

    cos 2

    cos 2 cos 2

    cos 2 cos 2

    sin 2 cos 21 1

    cos cos( ) sin2 2

    1 cos 421

    cos(4 ) si2

    c

    c c c c

    c c c

    s c c

    c c c s

    c c c

    c c s

    r t f t

    A m t f t f t

    n t f t f t

    n t f t f t

    A m t n t n t

    A m t f t

    n t f t n t

    +

    = + +

    + +

    +

    = + +

    + + +

    + + ( )n 4 cf t +

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    5.1 Effect of Noise on linear-Modulation Systems

    (2) DSB-SC AM)

    ) If PLL is employed

    )Assume

    )Message power :

    ( ) ( ) ( ) ( ) ( ) ( )1 1

    cos cos sin2 2

    c c c sy t A m t n t n t = + +

    coherent or synchronon demodc =

    ( ) ( ) ( )1 1

    0 2 2c c cy t A m t n t = = = +

    ( )

    ( )

    22

    0

    2

    2

    4

    04

    4

    c

    cM

    cM

    AP E M t

    AR

    AP

    =

    =

    =

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    5.1 Effect of Noise on linear-Modulation Systems

    (2) DSB-SC AM

    )Noise power :

    Note that :

    0

    1

    4

    cn nP P=

    -fc

    fc

    BPF

    nw

    (t) n(t)

    c sn n nP P P= =

    ( ) ( ) ( ) 2

    0 , -2

    0,

    n W

    c

    S f S f H f

    Nf f W

    otherwise

    =

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    5.1 Effect of Noise on linear-Modulation Systems

    (2) DSB-SC AM

    )

    ( )

    0

    2

    2

    0

    0 00

    2 22

    0, 0

    41 224

    2 2

    cM

    c M

    n

    c c MR

    R

    DSB b

    AP

    S P A P

    N P WNWN

    A A PP E M t

    S P S

    N N W N

    = = =

    = =

    = =

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    5.1 Effect of Noise on linear-Modulation Systems

    (3) SSB-AM) (3) SSB-AM

    with ideal-phase coherent demodulator

    ( ) ( ) ( ) ( ) ( )cos 2 sin 2ct c c cu t A m t f t A m t f t = ( ) ( ) ( )

    ( ) ( ) ( ) ( ) ( ) ( )cos 2 sin 2ct c c c s c

    r t u t n t

    A m t n t f t Am t n t f t

    = +

    = + +

    ( ) ( ) ( ) ( ) ( )1 1cos 22 2

    c c cy t LPF r t f t A m t n t= = +

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    5.1 Effect of Noise on linear-Modulation Systems

    (3) SSB-AM

    ( )

    0

    2

    0

    00

    -

    1

    4

    1 1 4 4

    22

    c

    c M

    n n n

    n n

    P A P

    P P P

    NP S f df W WN

    =

    = =

    = = =

    0

    20

    0, 0

    c M

    SSB n

    S P A P

    N P WN

    = =

    2 2

    2

    0,

    2 2c cR M c MM

    SSB b

    A Abut P P P A P

    S S

    N N

    = + =

    =

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    5.1 Effect of Noise on linear-Modulation Systems

    (4) Conventional AM) (4) Conventional AM

    for synchronous demodulation (similar to DSB, except using

    instead of m(t) )

    by a dc block

    ( ) ( ) ( )

    ( ) ( ) ( ) ( ) ( ) ( )

    1 cos 2

    1 cos 2 sin 2

    c n c

    c n c c s c

    u t A am t f t

    r t A am t n t f t n t f t

    = +

    = + +

    ( )1 nam t+ ( ) ( ) ( )

    1 11

    2 2c n cy t A am t n t = + +

    ( ) ( ) ( )1 1

    2 2c n cy t A am t n t= +

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    5.1 Effect of Noise on linear-Modulation Systems

    (4) Conventional AM

    but

    0

    2 2 00 0

    2 22 2

    0 00

    1 1 1 1, 4

    4 4 4 2 21

    41 22

    n c

    nn

    c M n n

    c Mc M

    NP A a P P p W N W

    A a P A a PS

    N N WN W

    = = = =

    = =

    22

    12 nc

    R M

    A

    P a P = + 2 22

    20, 0

    2 2

    2 20

    1

    1 2

    1 1

    nn

    n

    n n

    n n

    c MM

    A M M

    M MR

    bM M

    b b

    A a Pa PS

    N a P N W

    a P a PP Sa P N W a P N

    S S

    N N

    + = +

    = = + +

    =

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    5.1 Effect of Noise on linear-Modulation Systems

    (4) Conventional AM

    In practical application : 0.8 0.9

    0.1NM

    a

    P

    0, 1

    0, 0, 1,

    0.075 ,

    . . 11 ( 11 )

    AM b

    dB AM dB

    S S

    N N

    S Si e dB a lost of dB

    N N

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    5.1 Effect of Noise on linear-Modulation Systems

    (4) Conventional AM

    Envelope detector

    ( ) ( ) ( ){ } ( ) ( ) ( )

    ( ) ( ) ( ) ( )2

    2

    1 cos 2 sin 2

    1

    c n c c s c

    r c n c s

    r t A am t n t f t n t f t

    V t A am t n t n t

    = + +

    = + + +

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    5.1 Effect of Noise on linear-Modulation Systems

    (4) Conventional AMACase 1

    After removing the dc component,

    The same as y(t) for the synchronous demodulation, without the coefficient

    ( ) ( )( )

    ( ) ( )( ) ( ) ( )( )( ) ( ) ( )

    1 ( ) 1,

    1 ( ) 1, . . 1 ( )

    1 ( )

    c n

    s c n c n

    r c n c

    P n t A am t

    P n t A am t i e A am t n t

    V t A am t n t

    +

    + +

    + +

    ( ) ( ) ( )( )c n cy t A am t n t= +

    0, 2 0, 1

    under high SNR

    AM AM

    S S

    N N

    =

    ( ) ( )1 ( )c nA am t n t+

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    5.1 Effect of Noise on linear-Modulation Systems

    (4) Conventional AMACase 2 ( ) ( )1 ( )c nA am t n t+

    ( ) ( )( ) ( )( ) ( )

    ( )( ) ( ) ( ) ( ) ( )( )

    ( ) ( )

    ( )

    ( ) ( ) ( )(