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여섯째주

Digital Communications

Chapter 4Bandpass Modulation And Demodulation/Detection

Signal Processing Lab

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Block Diagram of a DCS

2

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4.2 Digital Bandpass Modulation Bandpass Modulation : The process of converting data signal to a

sinusoidal waveform where its amplitude, phase or frequency, or a combination of them, is varied in accordance with the transmitting data

Bandpass signal :

Where gT(t) is the baseband pulse shape with energy Eg

We assume here ( otherwise will be stated ) : gT(t) is a rectangular pulse shape with unit energy Gray coding is used for mapping bits to symbols; Es denotes average symbol energy given by

M

i is EM

E1

1

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Digital Bandpass Modulations (con’td)

One dimensional waveforms Amplitude Shift Keying ( ASK ) M-ary Pulse Amplitude Modulation ( M-PAM )

Two dimensional waveforms M-ary Phase Shift Keying ( M-PSK ) M-ary Quadrature Amplitude Modulation ( M-QAM )

Multidimensional waveforms M-ary Frequency Shift Keying ( M-FSK)

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Bandpass Digital Modulations

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Coherent Detections Coherent detectionRequires carrier phase recoveryNeeds circuits to perform phase estimation.

Source of carrier-phase mismatch Propagation delayOscillator mismatch

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Coherent Detections (cont’d)

)ˆ(

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Non-Coherent Detections

Does not require carrier phase recovery

Uses differential decoder or energy detectors

Less complexity at the price of higher error rate

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One Dimensional Modulation, Demodulation and Detection

Amplitude Shift Keying ( ASK ) modulation :

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One Dimensional mod.,….. (cont’d)

M-ary Pulse Amplitude modulation (M-PAM)

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One Dimensional mod.,….. (cont’d)

Coherent detection of M-PAM

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Two Dimensional Modulation, Demodulation and Detection

M-ary Phase Shift Keying (M-PSK)

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Two Dimensional mod.,….. (cont’d)

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Two Dimensional mod.,….. (cont’d)

Coherent detection of MPSK

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Two Dimensional mod.,….. (cont’d)

M-ary Quadrature Amplitude Mod. (M-QAM)

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Two Dimensional mod.,….. (cont’d)

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Two Dimensional mod.,….. (cont’d)

Coherent detection of M-QAM

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Multi-Dimensional Modulation, Demodulation and Detection (HW #4 p.202 Example 4.3)

M-ary Frequency Shift Keying ( M-FSK )

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Multi-Dimensional mod.,….. (cont’d)