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10-401-08-BandpassTransmissionDetection-1

# 10-401-08-BandpassTransmissionDetection-1 - Essential...

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Baseband Transmission 1 Essential Blocks:Digital Communication System Format Pulse Modulation Bandpass Modulation Transmitter Synchronization Format Detection Demodulation Sampling Receiver Channel 010100 0 T 2T 3T 4T 5T 6T 7T 8T 0 T 2T 3T 4T 5T 6T 7T

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Bandpass Modulation and Demodulation 2 Bandpass versus baseband modulation In digital communication system, digital symbols are transformed into waveforms that are compatible with the characteristics of the tranmission channel In baseband modulation , waveforms take the form of shaped pulses. In bandpass modulation , shaped pulses modulates a sinusoid called carrier wave or RF carrier For example, in radio transmission where the transmission medium is air, the shaped pulses should be converted to electromagnetic (EM) field. This is because EM is transmitted only via antennas whose dimensions are proportional to the wavelength (or frequency) of the EM signal Therefore, bandpass modulation is an essential step for radio transmission ! Haykin: Chapter 9 Sklar: Chapter 4
Bandpass Modulation and Demodulation 3 RF carrier signal General form of the sinusoid RF carrier s t = A t cos θ t A t : time-varying amplitude θ t : time-varying angle θ t = ω 0 t φ t Three distinguishing parameters of the sinusoid; -amplitude, -frequency and -phase Then, bandpass modulation can be performed by changing simply any of these parameters or their combinations. -1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 -1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 Bandpass: ASK/On-Off Keying

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Bandpass Modulation and Demodulation 4 Bandpass modulation schemes When the receiver has the knowledge about the phase of the carrier wave to detect signals, the process is called coherent detection Coherent Phase Shift Keying(PSK) Frequency Shift Keying(FSK) Amplitude Shift Keying(ASK) Continuous phase modulation (CPM) Hybrids Noncoherent Differerentially Phase Shift Keying(DPSK) Frequency Shift Keying(FSK) Amplitude Shift Keying(ASK) Continuous phase modulation (CPM) Hybrids
Bandpass Modulation and Demodulation 5 Bandpass Signaling: Amplitude and energy Waveform amplitude coefficient s t = A c cos ωt A c : peak value For sinusoidal waveform, A c = 2 A rms s t = 2 A rms cos ωt = 2A rms 2 cos ωt . Average normalized power for 1 resistor is given by P = A c 2 2 = A rms 2 , then s t = 2Pcos ωt = 2 E T cos ωt where E = PT power and energy relation

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Bandpass Modulation and Demodulation 6 Shift Keying Techniques: Waveforms
Bandpass Modulation and Demodulation 7 Basic bandpass modulation schemes

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10-401-08-BandpassTransmissionDetection-1 - Essential...

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