This ppt is a detailed description of modulation. It covers almost everything of amplitude modulation.

1. Modulation
Presented by-
Nidhi Baranwal
MCA 6th sem

2. What is Modulation?
• Operation of varying amplitude, frequency or phase of carrier signal
accordingly with the instantaneous amplitude of the message signal is
called modulation
• Modulation = Adding information to a carrier signal

3. Need for Modulation
• To transmit voice signal a large size antenna is required as antenna length is
proportional to half of wavelength. The size of the antenna will be more
than the distance between transmitter and receiver.
• Again when more than one transmitter is involved all station will overlap in
one frequency band.
• For those above reasons we choose a carrier, which is a high frequency
radio wave, can travel long distance without attenuation and as the
frequency is high smaller antenna is required. Selecting different carrier
frequency for different transmitting stations can eliminate overlapping of
frequency band.

4. Modulation System

5. Classification

6. Another way
• 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. It is classified as:
1. Amplitude Modulation
2. Frequency Modulation
3. Phase Modulation
• DIGITAL MODULATION:
If the variation in the parameter of the carrier is
discrete then it is termed as digital modulation technique. It is classified as:
1. Amplitude Shift Keying
2. Frequency Shift Keying
3. Phase Shift Keying

7. Amplitude Modulation
• AM is the process of varying the instantaneous amplitude of carrier signal
accordingly with instantaneous amplitude of message signal
• If m(t) is the message signal and c(t)= A cos wct then AM signal F(t) is
written as
F(t)= A cos wct+m(t) cos wct
or F(t)=[A+m(t)] cos wct

8. Frequency spectrum of Amplitude Modulation
• Frequency spectrum of AM comprises of:
• A lower side band whose highest frequency component is present at fc-fm
• An upper side band whose highest frequency component is present at fc+fm
• Carrier frequency fc
This type of amplitude modulation is known as double side band-full
carrier(DSB-FC)

9. Types of Amplitude Modulation
1. Double side band-full carrier(DSB-FC):
This is “standard” AM, used for
broadcasting. Here the carrier conveys no information
• Modulated wave envelope has same frequency as information signal
• Amplitude of modulated wave varies according to amplitude of information
signal

10. Contd…
2. Double side band-suppressed carrier(DSB-SC):
In this type, carrier wave is
absent so all the transmitted power is contained in LSB and USB
• Here frequencies produced by AM are symmetrically spaced above and
below the carrier frequency and the carrier level is reduced to the lowest
practical level, ideally being completely suppressed

11. Contd…
3. Single side band:
In SSB either the USB or LSB contains the complete
information of the message signal only one side band is necessary for
information transmission
• When only one side band is transmitted the modulation is called SSB

12. Contd…
4. Vestigial side band(VSB):
Limitation of single-sideband modulation being
used for voice signals and not available for video/TV signals leads to the usage
of vestigial sideband
• A vestigial sideband (in radio communication) is a sideband that has been
only partly cut off or suppressed.

13. Frequency Modulation
• FM is the process of varying the instantaneous frequency of carrier signal
accordingly with instantaneous amplitude of message signal
• Thus, if m(t) is the message signal and
c(t)=A cos wct then FM signal will be
F(t)= A cos (wct+kf ∫m(α)dα)

14. FM Signal Characters
• The FM wave is comprised of an infinite number of sideband components
• Bandwidth of an FM signal must be wider than that of an AM signal
• As the modulation index increases from mf = 0, the spectral energy shifts
from the carrier frequency to an increasing number of significant
sidebands.
• The higher the modulation index, the greater the required system
bandwidth
where n is the highest number of significant sideband components and
fm is the highest modulation frequency
• Carson’s rule
)(2 mfnBW 
)1(2)(2 fmm mffBW  

15. Generation of FM Signals
Narrow Band Frequency Modulation(NBFM):
• NBFM uses low modulation index values, with a much smaller range of
modulation index across all values of the modulating signal
• An NBFM system restricts the modulating signal to the minimum
acceptable value, which is 300 Hz to 3 KHz for intelligible voice
• Used in police, fire, and Taxi radios, GSM, amateur radio, etc
Wide Band Frequency Modulation(WBFM):
• When better signal quality is required Wideband FM (WBFM) is used at
the expense of greater spectrum usage. The term WBFM is used in
applications where the modulation index is equal to or larger than 1
• In such applications spectral efficiency is less important and sometimes
large spectral spread is actually desired

16. Phase Modulation
• PM is the process of varying the instantaneous phase of Carrier signal
accordingly with instantaneous amplitude of message signal
• Thus if m(t) is the message signal and c(t)=A cos wct then PM signal will be
F(t)= A cos (wct+kpm(t))

17. Digital Modulation

18. Amplitude Shift Keying
• In ASK, the amplitude of the signal is changed in response to information
and frequency & phase 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
• Thus this modulation scheme is known as on-off keying (OOK).
• Low bandwidth requirement & very susceptible to interference

19. Problems with ASK
• ASK transmission is highly susceptible to noise interference
• Unintentional voltages combine with the signal to change the amplitude
• High amount of energy is required
• In OOK one of the values is represented by no voltage
• The modulation process produces a complex signal that is combination of
many simple frequencies

20. Frequency Shift Keying
• When Data are transmitted by varying frequency of the carrier, we have the
case of frequency shift key
• In this modulation carrier has two predefined frequency wc1 and wc2.
When information bit is 1 carrier with wc1 is transmitted i.e. coswc1 and
When information bit is 0 carrier with wc0 is transmitted i.e. coswc0

21. Phase Shift Keying
• The phase of the carrier is shifted for this modulation. If the base band
signal m(t) =1 carrier in phase is transmitted. If m(t)=0 carrier with out of
phase is transmitted i.e. cos (wct+П)
• 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

22. Variants of PSK
• BPSK-Binary Phase Shift Keying
• QPSK - Quadrature Phase Shift Keying
• 8 PSK - 8 Point Phase Shift Keying
• 16 PSK - 16 Point Phase Shift Keying
• QAM - Quadrature Amplitude Modulation
• 16 QAM - 16 Point Quadrature Amplitude Modulation
• 64 QAM - 64 Point Quadrature Amplitude Modulation
• DPSK- Differential Phase Shift Keying
• MSK - Minimum Shift Keying
• GMSK - Gaussian filtered Minimum Shift Keying

23. Contd…
• BPSK:
• QPSK:

24. Contd…
• 8 PSK:
• 16 PSK:

25. Quadrature Amplitude Modulation
• QAM is a combination of FSK & PSK so that a maximum contrast b/w
each signal unit is achieved
• If we have x variations in phase and y variations in amplitude giving us x
times y possible variations and the corresponding number of bits per
variation

26. 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

27. Metrics of Digital Signal
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 accommodate data within a limited bandwidth
• Trade off between data rate and pulse width
• Easy to implement and cost-effective to operate.

28. Pulse Modulation
• The process of transmitting signals in the form of pulses (discontinuous
signals) by using special techniques.
• Typical Signal
1. Pulse Amplitude Modulation(PAM)
2. Pulse Width Modulation(PWM)
3. Pulse Position Modulation(PPM)
4. Pulse Code Modulation(PCM)

29. Contd…
• PAM: The signal is sampled at regular intervals such that each sample is
proportional to the amplitude of the signal at that sampling instant. This
technique is called “sampling”
• PWM: In this type, the amplitude is maintained constant but the duration or
length or width of each pulse is varied in accordance with instantaneous
value of the analog signal
• PPM: In this type, the sampled waveform has fixed amplitude and width
whereas the position of each pulse is varied as per instantaneous value of
the analog signal
• PCM: Analog to digital converter employs following technique:
1. Sampling
2. Quantization
3. Line coding

30. Thank You