TABLE OF CONTENTS To transmit a signal across a wireless channel it is necessary to modulate this signal onto a carrier. Modulation is defined [27] as the process of imparting the source information onto a band-pass signal with a carrier frequency f c by the introduction of amplitude, frequency and/or phase perturbations. The bandpass signal generated is called the modulated signal s(t), and the baseband source signal is called the modulating signal m(t).
If the modulating baseband signal m(t) is a digital signal the modulation technique is a digital modulation technique. Digital modulation techniques can be classified into three groups depending on which parameter of the sinusoidal carrier the digital wave modulates. A sinusoidal carrier such as:
| (4.1) |  |
is defined by three parameters, the amplitude A c , the frequency f c= w c/(2 ?) and the phase 
. The subscript c denotes the carrier .
If the digital signal modulates the amplitude, that modulation scheme is called amplitude modulation. Digital amplitude modulation schemes are presented in section 4.2. If the digital signal modulates the phase, that modulation scheme is called phase modulation. Digital phase modulation schemes (both binary and quadrature) are presented in section 4.3. If the digital signal modulates the frequency, that modulation scheme is called frequency modulation. Digital frequency modulation schemes are presented in section 4.4. Frequency and phase modulation are sometimes grouped together under the name angle modulation. Hybrid modulation schemes also exist, these are a combination of more than...
