High Level Modulation Techniques
Modulation describes a range of techniques for encoding information on a carrier signal, a device that performs modulation is known as a modulator. Modulation is frequently used in conjunction with various channel access methods.
Amplitude modulation (AM) - the amplitude of the wave is modulated to be directly proportional to the value of the analog signal at the time.
Frequency modulation (FM) - the variation of instantaneous frequency in accordance with an input signal.
Quadrature Amplitude Modulation (QAM) - the variation of the amplitude of both the carrier wave and a 'quadrature' carrier that is 90Â° out of phase with the main carrier in accordance with two input signals. Phase modulation can also be regarded as a special case of quadrature amplitude modulation, where the amplitude of the modulating signal is constant, with only the phase varying.
Frequency-shift keying (FSK) - is frequency modulation in which the modulating signal shifts the output frequency between predetermined values.
Gaussian Minimum Shift Keying (GMSK) is a type of Continous Phase Modulation and is a spectrally efficient modulation form, but it needs higher power level than QAM.