Modulation

 Modulation

Modulation is the process of impressing a low-frequency intelligence signal onto a high-frequency carrier signal.

1        DSC-with carrier Modulation(AM)

Amplitude Modulation (AM) is a process that a high-frequency carrier signal is modulated by a low-frequency modulating signal (usually an audio). In amplitude modulation the carrier amplitude varies with the modulating amplitude.

2        DSC-SC Modulation:

In double side band suppressed carrier modulation low frequency message is multiplied with high frequency carrier. Two bands upper side band and lower side band is generated in the result of this modulation.

3        SSB Modulation:

In single side band modulation both the bands of double side bands USB (upper side band) and LSB (lower side band) are not present one band is transmitted at one time. Phase shifting of carrier and Hilbert transform is used in this technique.

4        VSB Modulation:

Vestigial side band also called asymmetric side band is comprised between DSB and SSB. In VSB instead of rejecting one side band completely like in SSB a gradual cutoff of one side band is accepted. 

5        QAM Modulation:

3.3.1 

Quadrature amplitude modulation is used to overcome the disadvantage of DSB modulation of double band width. In QAM we can transmit two messages instead of one in this we can utilize double bandwidth. We can transmit two messages by phase shifting of the same carrier and then multiply one message with one carrier and other message with the shifted version of the same carrier.