Module IIITaub Ch.6

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Module III Taub Ch.6 PSK QPSK M-ary PSK FSK M-ary FSK MSK

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Examples of Modulation Amplitude Shift Keying (ASK) or On/Off Keying (OOK): Frequency Shift Keying (FSK): Phase Shift Keying (PSK):

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Description of binary ASK,PSK, and FSK schemes Bandpass binary data transmission system Modulator Channel Hc(f) Demodulator (receiver) {bk} Binary data Input {bk} Transmit carrier Clock pulses Noise n(t) Clock pulses Local carrier Binary data output Z(t) + + V(t) ?+

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Binary information over bandpass channels

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Digital modulation and channel

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Digital Demodulator

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Signal Regeneration

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Bandwidth of signal Baseband versus bandpass:

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Scheme to recover the baseband signal in BPSK

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Spectrum of BPSK

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PSD of NRZ data b(t) & binary PSK

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Geometrical Representation of BPSK Signals

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Differential Phase-Shift Keying Merit – it eliminate the ambiguity about whether the demodulated data is or is not inverted. Avoids the need to provide the synchronous carrier required at the demodulator for detecting a BPSK signal. Arbitrarily assuming that in the first interval b(0)=0. In the demodulator, the data will be correctly determined regardless of our assumption concerning b(0) - Invariant feature of the system. i.e no change in b(t) occur whenever d(t)=0, and a change in b(t) occurs whenever d(t)=1. When d(t)=0 the phase of the carrier does not change at the beginning of the bit interval, while when d(t)=1 there is a phase change of magnitude ?.

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Means of generating a DPSK signal

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Logic waveforms to illustrate the response b(t) to an input d(t)

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Method of recovering data from the DPSK signal

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Cont.. The transmitted data d(t) can be readily determined from the product b(t)b(t-Tb). If d(t)=0 then there was no phase change and b(t)=b(t-Tb) both being +1V or both being -1V. In this case b(t)b(t-Tb)=1. If however d(t)=1 then there was a phase change and either b(t)=1V with b(t-Tb)= -1V or vice versa. In either case b(t)b(t-Tb)= -1.

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Type-D flip-flop

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Quadrature Phase-Shift Keying (QPSK) BW for BPSK must be nominally 2fb. QPSK allows bits to be transmitted at half the BW. In a QPSK system the type D flip-flop is used as a one bit storage device.

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An offset QPSK Transmitter

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Waveforms for the QPSK Transmitter

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Phasor diagram for sinusoids in QPSK Transmitter

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A QPSK Receiver Carrier Recovery Circuit

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Signal Space Representation

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The four QPSK signal drawn in signal space 2 2

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M-ary PSK

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Geometrical representation of M-ary PSK signals

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M-ary PSK Transmitter

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M-ary PSK receiver

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BFSK signal generator

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Spectrum of BFSK

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The PSD of individual terms

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A BFSK Receiver

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Geometrical Representation of Orthogonal BFSK

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Signal space representation orthogonal / non-orthogonal

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An M-ary Communication System

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M-ary FSK

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Power Spectral Density of M-ary FSK (four frequencies)

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Geometrical Representation of orthogonal M-ary FSK (M=3) when the frequencies are selected to generate orthogonal signals

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