*5.1.2 Application*

*Multiplexing*

**5. Major digital modulation schemes**

nication we use the following schemes:

• Amplitude shift keying (ASK)

• Frequency shift keying (FSK)

which the unipolar pulses are present.

*5.1.1 ASK advantages and disadvantages*

inexpensive.

noise interference.

• Phase shift keying (PSK)

**5.1 Amplitude shift keying**

In analog communication we use different modulation schemes like amplitude modulation, frequency modulation, phase modulation, etc. [9]. In digital commu-

The principle of amplitude shift keying is that the amplitude of the carrier wave is modulated in accordance with the digital message signal, i.e., ASK signal represents the binary data in the form of variations in the amplitude of the carrier signal. When an ON condition of digital pulse exists, then carrier will be switched ON, and when an OFF condition encounters, the carrier will be switched OFF. The time period for which the carrier is present or absent depends on the time interval for

Here the amplitude of carrier signal is varied to represent binary 1 and binary 0 data inputs, while the frequency and phase of the carrier signal remain constant.

The major advantage of ASK includes high bandwidth efficiency and simplicity in its design. In ASK the modulation and demodulation processes are comparatively

Its disadvantages include lower power efficiency, and it is very susceptible to

Voltage levels are left to designers of the modulation system (**Figure 20**).

**24**

**Figure 20.**

*Amplitude shift keying.*

