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

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

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

Binary information over bandpass channels

Digital modulation and channel

Digital Demodulator

Signal Regeneration

Bandwidth of signal Baseband versus bandpass: Baseband signal Bandpass signal Local oscillator

BPSK-Transmitter

Scheme to recover the baseband signal in BPSK

BPSK-Receiver

Cont..

Spectrum of BPSK

PSD of NRZ data b(t) & binary PSK

Geometrical Representation of BPSK Signals

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.

Means of generating a DPSK signal

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

Method of recovering data from the DPSK signal

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

Type-D flip-flop

Quadrature Phase-Shift Keying (QPSK) BW for BPSK must be nominally 2f b. 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.

An offset QPSK Transmitter

Waveforms for the QPSK Transmitter

OQPSK

Phasor diagram for sinusoids in QPSK Transmitter

A QPSK Receiver Carrier Recovery Circuit

Signal Space Representation

The four QPSK signal drawn in signal space 2 2

M-ary PSK

Geometrical representation of M-ary PSK signals

Cont..

M-ary PSK Transmitter

M-ary PSK receiver

BFSK

BFSK signal generator

Spectrum of BFSK

The PSD of individual terms

A BFSK Receiver

Geometrical Representation of Orthogonal BFSK

Signal space representation orthogonal / non-orthogonal

An M-ary Communication System

M-ary FSK

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

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

MSK