This document discusses various digital modulation techniques. It begins by defining modulation as adding information to a carrier signal. It then distinguishes between analog and digital modulation. Digital modulation modulates an analog carrier signal with a discrete signal, and can be considered as converting digital-to-analog and vice versa. Some key digital modulation techniques discussed include amplitude shift keying (ASK), frequency shift keying (FSK), phase shift keying (PSK), quadrature amplitude modulation (QAM), and differential phase shift keying (DPSK). Metrics for comparing digital modulation techniques include power efficiency, bandwidth efficiency, and implementation cost-effectiveness.

1. DIGITAL MODULATION TECHNIQUES
Presented By:
NIDHI BARANWAL
MCA 3rd SEMESTER
University of Allahabad

2. WHAT IS MODULATION
• Modulation = Adding information to a carrier signal
• The sine wave on which the characteristics of the information signal are
modulated is called a carrier signal

3. CONTD.

4. MODULATION SYSTEMS

5. TYPES OF MODULATION
 ANALOG MODULATION: If the variation in
the parameter of the carrier is continuous in
accordance to the input analog signal the
modulation technique is termed as analog
modulation scheme
 DIGITAL MODULATION: If the variation in the
parameter of the carrier is discrete then it is
termed as digital modulation technique

6. ANALOG MODULATION

7. DIGITAL MODULATION
• In digital modulation , an analog carrier signal is
modulated by a discrete signal
• Digital modulation can be considered as digital-
to-analog and the corresponding demodulation
as analog-to-digital conversion
• In digital communications, the modulating wave
consists of binary data and the carrier is
sinusoidal wave

8. DIGITAL MODULATION TECHNIQUES

9. AMPLITUDE SHIFT KEYING
 In ASK, the amplitude of the signal is changed in
response to information and all else is kept fixed
 Bit 1 is transmitted by a signal of one particular
amplitude. To transmit 0,we change the amplitude
keeping the frequency constant

10. FREQUENCY SHIFT KEYING
 In FSK, we change the frequency in response to
information
 one particular frequency for a 1 and another
frequency for a 0

11. PHASE SHIFT KEYING
 In PSK, we change the phase of the sinusoidal carrier to
indicate information. Phase in this context is the starting
angle at which the sinusoidal starts
 One phase change encodes 0 while another phase
change encodes 1.To transmit 0,we shift the phase of the
sinusoid by 180

12. M-ARY MODULATION TECHNIQUE
 In binary data transmission, send only one of two
possible signals during each bit interval Tb
 In M-ary data transmission, send one of M
possible signals during each signaling interval T
 In almost all applications, M = 2n and T = nTb,
where n is an integer
 Each of the M signals is called a symbol
 These signals are generated by changing the
amplitude, phase, frequency, or combined forms
of a carrier.
 Thus, we have: MASK MPSK MFSK MQAM

13. QUADRATURE PHASE SHIFT KEYING
 Quadrature Phase Shift Keying can be
interpreted as two independent BPSK systems
, and thus the same performance but twice the
bandwidth efficiency
 The phase of the carrier takes on 1 of 4 equally
spaced values where each
value of phase corresponds to a unique pair of
message bits

14. QUADRATURE AMPLITUDE MODULATION
 If both the amplitude and the phase are varied
proportional to the information signal,
quadrature amplitude modulation results.
 Combination of phase shifting and amplitude
shifting

15. DIFFERENTIAL PHASE SHIFT KEYING
 For the perfect detection of a phase modulated
signal, the receiver needs a reference signal
but if differential encoding and phase shift
keying are made together at the transmitter
the technique is called as Differential Phase
Shift Keying
 For the transmission of a symbol 1, the phase
is unchanged whereas for transmission of
symbol 0, the phase of the signal is changed
by 180

16.  In DPSK, the phase shift is with reference
to the previous bit transmitted rather than
to some constant reference signal
CONTD..

17. METRICS FOR DIGITAL MODULATION
 POWER EFFICIENCY
 Power efficiency is a measure of how much signal
power should be increased to achieve a particular bit error
rate (BER) for a given modulation scheme
 Ability of a modulation technique to preserve the fidelity of
the digital message at low power
 Designer can increase noise immunity by increasing
signal
power
 BANDWIDTH EFFICIENCY
 Ability to accomodate data within a limited bandwidth
 Tradeoff between data rate and pulse width
 Easy to implement and cost-effective to operate.

18. THANKS