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Μέρος Α : Τηλεπικοινωνιακά Θέματα: Τεχνικές Ψηφιακής Διαμόρφωσης και Μετάδοσης PowerPoint PPT Presentation


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Τμήμα Μηχανικών Η/Υ και Πληροφορικής. Εργαστήριο Επεξεργασίας Σημάτων και Τηλεπικοινωνιών. Κινητά Δίκτυα Επικοινωνιών. Μέρος Α : Τηλεπικοινωνιακά Θέματα: Τεχνικές Ψηφιακής Διαμόρφωσης και Μετάδοσης. T ο γενικό διάγραμμα ενός Ψηφιακού Τηλ/κού Συστήματος.

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Μέρος Α : Τηλεπικοινωνιακά Θέματα: Τεχνικές Ψηφιακής Διαμόρφωσης και Μετάδοσης

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/

: :


T /


  • : .

  • (passband). (baseband) .

  • : .

  • .


  • , :

    -

    ( / )

    -

    -

    (constant envelop / power efficiency)

    -

    (Spectral efficiency)

    * Power efficiency: Watt

    ( : CNR, Es/No )

    * Spectral efficiency: Hz (bits/sec/Hz).


  • (, , ).

  • .

  • (.. IS-95).


  • :

    • , ,

    • H/W S/W.

  • : ASK (Amplitude Shift Keying)

    FSK (Frequency Shift Keying)

    PSK (Phase Shift Keying)


  • (coherent) : .

  • (incoherent) : (detection) .

  • PSK DPSK ( PSK)

  • Incoherent FSK (. )

cos(2fit ) =

cos() cos(2fit ) + sin() sin(2fit)


  • spectral efficiency:

  • Quadrature Amplitude Modulation (QAM M)

    s(t) = Am gT(t)cos(2fct + n)

    s(t) = AmcgT(t)cos(2fct ) + AmsgT(t)sin(2fct ) , m=1,2 M


  • Quadrature Phase Shift Keying (QPSK)

  • QAM =4.


QPSK

Split to odd and even


QPSK


  • : Offset QPSK ( OQPSK )

  • QPSK . pulse shaping ( !)

  • OQPSK (. Q) Tb( QPSK). Tb( 2Tb) 90( 180).


pulse shaping


  • QPSK: (/4)-QPSK

  • QPSK OQPSK

  • H 135. QPSK OQPSK.

  • Ts .

  • OQPSK .

    (/4)-QPSK


  • .

  • FM FSK.

    :

  • ( carrier recovery)

  • -

  • :

  • BER ( )

  • spectral inefficiency ( )

  • ( FSK - )

  • (, BER )

-


  • M-FSK

  • minf = 1/2Ts

  • minf = 1/Ts

  • CPFSK (continuous phase frequency shift keying)

  • ( ) CPFSK MSK (minimum shift keying). OQPSK. I Q (sinusoidal pulse shaping)

-


MSK

-

*


-

* FFSK (Fast FSK): MSK


MSK

-


  • MSK: GMSK (Gaussian MSK)

  • - ( Gauss)

-

* Bb : Bandwidth of the premodulation pulse shaping filter

* To : Symbol period


MSK GMSK

-


  • OFDM : Orthogonal Frequency Division Multiplexing

  • H OFDM () 1/s , s OFDM.

() OFDM

(ISI)


:

() OFDM

Multicode Transmission

Multicarrier Transmission


  • OFDM - inter-carrier interference. - .

() OFDM

FDM

OFDM

* :


  • () OFDM sub-channel () OFDM.

() OFDM

  • :

    -

    - . burst errors.

  • :

    - carrier frequency offset ( jitter Doppler )

    -


OFDM

() OFDM


  • OFDM DFT. DFT -

() OFDM

:

fi

i-o - f(t) pulse waveform

fi = fo + (i/Ts)


() OFDM IDFT

- IDFT -- (P/S) OFDM ( ( QAM ) -)

- Q - ( IDFT ) -


Guard Interval

() OFDM


Bit Error Probability Curves for OFDM and QPSK

() OFDM


() OFDM

(cyclic prefix).


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