Modulation Scheme

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The Modulator converts an input signal into a form suitable for RF transmission. The Demodulator recovers the original signal. Since the RF signal is a based sine wave oscillating around the transmission frequency, the Modulator has to modulate this sine wave in a way so that all information is transmitted and well-recoverable but only as little Bandwidth as allowed is allocated.

The more the Modulation Scheme modifies the original sine wave the more the Frequency of the RF sine wave will vary -- the higher the Bandwidth will be.


Analog Modulation Schemes
Shortform Name
AM Amplitude Modulation
FM Frequency Modulation
PM Phase Modulation


Digital Modulation Schemes
Shortform Name
BPSK Binary Phase Shift Keying
QPSK Quadrature Phase Shift Keying
QAM-16 16-state Quadrature Amplitude Modulation
QAM-32 32-state Quadrature Amplitude Modulation
QAM-64 64-state Quadrature Amplitude Modulation
QAM-128 128-state Quadrature Amplitude Modulation
QAM-256 256-state Quadrature Amplitude Modulation
8VSB 8-state Vestigial Side Band Modulation
OFDM
DMT
Orthogonal frequency division modulation
Discrete multitone modulation


If you interested in the inner workings and the theory behind demodulators for digital TV, there are some signal processing tutorials at http://www.complextoreal.com/.