Digital Modulation and various technique

Digital modulation is the process of encoding a digital information signal into the amplitude, phase, or frequency of the transmitted signal. The encoding process affects the bandwidth of the transmitted signal and its robustness to channel impairments.

1. Digital Modulation Techniques

2. Digital Modulation techniques (part 2)
Bandpass data transmission
Amplitude Shift Keying (ASK)
Phase Shift Keying (PSK)
Frequency Shift Keying (FSK)
QuadratureAmplitude Modulation (QAM)

3. Digital Modulation Techniques
Digitalmodulation
Theprocessbywhichdigitalsymbolsare
transformedintowaveformsthatarecompatible
withthecharacteristicofthechannel.
Bandpassmodulation
Processwherebytheamplitude,frequency,or
phaseofanRFcarrier,oracombinationofthem,
isvariedinaccordancewiththeinformationtobe
transmitted.

4. Digital BandpassModulation
A carrier signal has three parameters which can be
used for impressing:
Amplitude
FrequencyPhase

5. Digital BandpassModulation
•Iftheamplitude,Vofthecarrieris
variedproportionaltotheinformation
signal,adigitalmodulatedsignalis
calledAmplitudeShiftKeying(ASK)
•Ifthefrequency,fofthecarrieris
variedproportionaltotheinformation
signal,adigitalmodulatedsignalis
calledFrequencyShiftKeying(FSK)

6. Digital BandpassModulation
If the phase, θof the carrier is varied
proportional to the information signal, a
digital modulated signal is called Phase
Shift Keying (PSK)
If both the amplitude,V and the phase, θof
the carrier are varied proportional to the
information signal, a digital modulated
signal is called Quadrature Amplitude
Modulation (QAM)

7. Amplitude Shift Keying (ASK)
ASK demonstrates poor performance, as it is
heavily affected by noise and interference.
Used in radio telegraphy in the early 1900s

8. Amplitude Shift Keying (ASK)
Mwaschosentobeequalto2,soitis
correspondingtotwowaveformtypes.
AlsoknowasBinaryASKsignaling(alsocalled
on-offkeying)

9. Frequency Shift Keying (FSK)
Bandwidth occupancy of FSK is dependant on the
spacing of the two symbols. A frequency spacing of
0.5 times the symbol period is typically used.
FSK can be expanded to a M-aryscheme, employing
multiple frequencies as different states.

10. Frequency Shift Keying (FSK)
M was chosen to be equal to 3, corresponding to the 3
waveform types (3-ary).
Emphasize the mutually perpendicular axes.
The signal set is characterized by Cartesian
coordinates, such that each of the mutually
perpendicular axes represents a sinusoid with a
different frequency.
Such mutually perpendicular vectors are called orthogonal
signals.

11. Phase Shift Keying (PSK)
Phase Shift Keying (PSK) demonstrates better performance
than ASK and FSK.
PSK can be expanded to a M-aryscheme, employing multiple
phases and amplitudes as different states.
Filtering can be employed to avoid spectral spreading.
Widely used in both military and commercial communications
system.

12. Phase Shift Keying (PSK)
M was chosen as to be as 2, and it is called binary
PSK (BPSK)
The modulating signal shifts the phase of the wave
si(t) to one of two states, either zero or π(180º).
For the BPSK example, the vector picture illustrates
the two 180º opposing vectors.
Signal sets that can be depicted with such opposing
vectors are called antipodal signal sets.

13. Phase Shift Keying (PSK)
Constellation of two-level PSK

14. Phase Shift Keying (PSK)

15. Phase Shift Keying (PSK)
4-PSKhasmoreefficientusageofbandwidththan2-
PSK,becauseeachsignalunithastwobits.Forthe
samebandwidth,thedatabitratedoubles.

16. Phase Shift Keying (PSK)
Excellent performance of 2-PSK encourages us to go
with 4-PSK, also called quadraturePSK (Q-PSK)

17. Phase Shift Keying (PSK)
Theideacanbeextendedto8-PSK,16-PSK,32-
PSK,….
Thelimitationistheabilityofequipmentto
distinguishsmalldifferencesinsignal’sphase.
8 PSK

18. BPSK Modulator
BinaryPSK(BPSK)modulationcanbeaccomplished
bysimplymultiplyingtheoriginalsignald(t)(which
isabinaryrandomsequence)bythecarriersignal,
whichisananalogsinusoidaloscillation.After
multiplicationabandpassfilterisrequired

19. QPSK Modulator

20. QuadratureAmplitude Modulation
(QAM)
CombinationofASKandPSKwhichhelpsmakinga
contrastbetweensignalunits.Thenumberof
amplitudeshiftsshouldbelowerthanthenumberof
phaseshiftsduetonoisesusceptibilityofASK.

21. QuadratureAmplitude Modulation
(QAM)

22. Summarize