Modulation Techniques

Analog Modulation Techniques

There are three basic analog modulation techniques used for analog source signal.

AM (Amplitude Modulation)

FM (Frequency Modulation)

PM (Phase Modulation)

                            

Digital Modulation Techniques

There are two ways for digital transmission or we can say that there are two ways to transmit a digital signal from one point to another.

                  Baseband transmission.

                  Band-pass transmission (in some books it is considered analog transmission)

A baseband signal ("digital-over-digital" transmission): A sequence of electrical pulses or light pulses produced by means of a line coding scheme such as Manchester coding. This is typically used in serial cables, wired local area networks such as Ethernet, and in optical fiber communication. It results in a pulse amplitude modulated signal, also known as a pulse train.

A band-pass signal ("digital-over-analog" transmission): A modulated sine wave signal representing a digital bit-stream. Note that this is in some textbooks considered as analog transmission, but in most books as digital transmission. The signal is produced by means of a digital modulation method such as PSK, QAM or FSK. The modulation and demodulation is carried out by modem equipment. This is used in wireless communication, and over telephone network local-loop and cable-TV networks.

There are three basic digital modulation techniques used for analog transmission of digital data. These modulation methods can be considered as digital to analog conversion and they are also known as Pass-band modulation techniques.

►   ASK – Amplitude-Shift Keying

►   FSK – Frequency-Shift Keying

►   PSK – Phase-Shift Keying

And one digital modulation techniques used for digital transmission of digital data.

►   Line coding. (Also known as digital baseband modulation technique).

Amplitude Shift-Keying (ASK)

 

Frequency Shift-Keying (FSK)

  

Note:

Quadrature amplitude modulation (QAM) is both an analog and a digital modulation scheme. 

Listening lectures on computer is digital communication which is much cleaner than analog communication such as over phone line. In digital world we don’t use the property of the medium; rather we use 1s and 0s. The words that are coming out of the instructor mouth are transforming into 1s and 0s which could be transmitted over anything, that why it is considered digital. It’s not really using the properties of Ethernet to send stuff to you.