Slide 0

Module IIITaub Ch.6
PSK
QPSK
M-ary PSK
FSK
M-ary FSK
MSK

Slide 1

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

Slide 2

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)
?+

Slide 3

Binary information over bandpass channels

Slide 4

Digital modulation and channel

Slide 5

Digital Demodulator

Slide 6

Signal Regeneration

Slide 7

Bandwidth of signal
Baseband versus bandpass:

Slide 8

BPSK-Transmitter

Slide 9

Scheme to recover the baseband signal in BPSK

Slide 10

BPSK-Receiver

Slide 11

Cont..

Slide 12

Spectrum of BPSK

Slide 13

PSD of NRZ data b(t) & binary PSK

Slide 14

Geometrical Representation of BPSK Signals

Slide 15

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 ?.

Slide 16

Means of generating a DPSK signal

Slide 17

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

Slide 18

Method of recovering data from the DPSK signal

Slide 19

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.

Slide 20

Type-D flip-flop

Slide 21

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.

Slide 22

An offset QPSK Transmitter

Slide 23

Waveforms for the QPSK Transmitter

Slide 24

OQPSK

Slide 25

Phasor diagram for sinusoids in QPSK Transmitter

Slide 26

A QPSK Receiver
Carrier
Recovery
Circuit

Slide 27

Signal Space Representation

Slide 28

The four QPSK signal drawn in signal space
2
2

Slide 29

M-ary PSK

Slide 30

Geometrical representation of M-ary PSK signals

Slide 31

Cont..

Slide 32

Cont..

Slide 33

M-ary PSK Transmitter

Slide 34

M-ary PSK receiver

Slide 35

BFSK

Slide 36

BFSK signal generator

Slide 37

Spectrum of BFSK

Slide 38

The PSD of individual terms

Slide 39

A BFSK Receiver

Slide 40

Geometrical Representation of Orthogonal BFSK

Slide 41

Signal space representation orthogonal / non-orthogonal

Slide 42

An M-ary Communication System

Slide 43

M-ary FSK

Slide 44

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

Slide 45

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

Slide 46

MSK