Summary: Continuous-wave (Analog) Modulation

Modulated Signal /

Mathematical Expression

/ Bandwidth (Hz) / Type of De -modulation / Figure of Merit (FOM) / Areas of Application
Double Side-Band Suppressed Carrier (DSB-SC) / / 2B / Coherent / 1 / Radio Systems
Amplitude Modulation (AM) / / 2B / Coherent or Non-coherent / / Radio Systems
Quadrature Amplitude Modulation (QAM) / / 2B / Coherent / 1 / Chrominance TV signals
Single Side-Band (SSB) / /

B

/ Coherent / 1 / Telephone Systems
Single Side-Band plus Carrier (SSB+C) / /

B

/ Non-Coherent / / Telephone Systems
Vestigial Side-Band (VSB) / / (1.25)B / Coherent / 1 / TV Systems
Vestigial Side-Band plus Carrier (VSB+C) / / (1.25)B / Non-coherent / / TV Systems
Frequency Modulation (FM) / / 2(Df+B) / Coherent (PLL) or Non-coherent / / Radio and TV Audio
Phase Modulation (PM) / / 2(Df+B) / Coherent (PLL) or Non-coherent / / Radio and TV Audio

Notations

·  m(t), m1(t), and m2(t) are baseband signals with bandwidths 2pB rad/s or B Hz.

·  wc=2pfc is the carrier frequency in rad/s ( fc B).

·  is the Hilbert transform of m(t), defined as:

·  ms(t) is obtained by passing m(t) through a filter with frequency response:, where Hi(w) is the vestigial filter.

·  In the expressions of jSSB(t) and jSSB+C(t), the minus (-) sign is for upper side-band (USB) case and the plus (+) sign is the lower side-band (LSB) case.

·  In the expressions of jVSB(t) and jVSB+C(t) the plus (+) sign is for upper vestigial side-band (USB) case and the minus (-) sign is the lower vestigial side-band (LSB) case.

·  SSB and VSB modulations are sometimes referred to as SSB-SC and VSB-SC.

·  In practice FM and PM are not used in their pure theoretical forms. Instead, a mixture of both schemes is used and the resulting modulated signal takes the form , where h(t) is the impulse response of a filter called "pre-emphasis filter". (Notice that if h(t)=kpd(t), we get PM signal and if h(t)=kfu(t), we get FM signal. u(t) is the unit step function.)

·  FOM is defined as: FOM = SNRo/SNRi, where SNRi and SNRo are, respectively, the signal-to-noise ratios at the input and output of the receiver. FOM gives the gain (or loss) of the receiver in terms of SNR.

·  Pm is the average power of the message signal m(t) and is defined as: , where Sm(w) is the PSD of m(t).

·  FOM expressions for FM and PM are valid for both narrow-band and wide-band cases. However, FOM for AM may also be applied to NBFM and NBPM since the latter are similar to AM modulation.

·  The comparison between FM and PM performances can be made by taking the ratio FOMPM/FOMFM = (2pBmp)2/3(mp')2. If this ratio is greater than 1, PM is superior than FM, otherwise FM is superior.