25-05-2012, 05:32 PM
Modulation and Demodulation Techniques in Communication Systems
[attachment=23069]
Classification of Modulation Techniques
mModulation Techniques can be broadly classified as follows:
l Digital versus Analog Modulation
l Baseband versus Bandpass (Passband) Modulation
l Binary versus M-ary Modulation
l Memoryless Modulation versus Modulation with memory
l Linear versus Nonlinear Modulation
l Constant envelope versus Non-constant envelope Modulation
l Power efficient versus Bandwidth efficient Modulation
Why Modulate?
Coupling EM wave into space - antenna size a wavelength l
For speech signal f = 3 kHz ð l = 105m
Antenna size without modulation @ l = 105m = 60 miles
Practically unrealizable
Hence, efficient antenna of realistic physical size is needed for
radio communication system
mInformation signal must conform to the limitation of its channel
(channel matching)
Reduce the effect of interference, e.g. Spread Spectrum
Place signals at desired frequency band for signal processing purposes
such as filtering, amplification, multiplexing
Used to map digital information sequence into waveforms
Analog Modulation Techniques
These types of modulation are carrier/continuous wave modulation
In this case, the Intermediate Frequency (IF) or the Radio
Frequency (RF) is modulated
Frequency & Phase Modulation are also known as Angle Modulation
Amplitude Modulation (AM) is used whenever a shift in the
frequency components of a given signal is desired
l E.g., transmitting voice signal (3 kHz) via EM wave requires that
3 kHz be raised several orders of magnitude before transmission
[attachment=23069]
Classification of Modulation Techniques
mModulation Techniques can be broadly classified as follows:
l Digital versus Analog Modulation
l Baseband versus Bandpass (Passband) Modulation
l Binary versus M-ary Modulation
l Memoryless Modulation versus Modulation with memory
l Linear versus Nonlinear Modulation
l Constant envelope versus Non-constant envelope Modulation
l Power efficient versus Bandwidth efficient Modulation
Why Modulate?
Coupling EM wave into space - antenna size a wavelength l
For speech signal f = 3 kHz ð l = 105m
Antenna size without modulation @ l = 105m = 60 miles
Practically unrealizable
Hence, efficient antenna of realistic physical size is needed for
radio communication system
mInformation signal must conform to the limitation of its channel
(channel matching)
Reduce the effect of interference, e.g. Spread Spectrum
Place signals at desired frequency band for signal processing purposes
such as filtering, amplification, multiplexing
Used to map digital information sequence into waveforms
Analog Modulation Techniques
These types of modulation are carrier/continuous wave modulation
In this case, the Intermediate Frequency (IF) or the Radio
Frequency (RF) is modulated
Frequency & Phase Modulation are also known as Angle Modulation
Amplitude Modulation (AM) is used whenever a shift in the
frequency components of a given signal is desired
l E.g., transmitting voice signal (3 kHz) via EM wave requires that
3 kHz be raised several orders of magnitude before transmission