Modulation is the process of transforming a carrier signal so that it can carry the information of a message signal. It superimposes the contents of the message signal over a high-frequency carrier signal, which is then transmitted over communication channels.
Modulation can be of two types −
Here, the analog information signal is transformed to the analog carrier signal so that it can travel large distances without substantial loss.
Analog modulation can be of three types −
Digital modulation is the process of converting a digital bit stream into an analog carrier wave for transmission via a communication channel.
Digital modulation is broadly divided into two categories −
Bandpass Modulation as in baseband transmission:
Here, the bits are converted directly into signals.
Passband Modulation as in passband transmission:
Here, the amplitude, phase or frequency of the carrier signal is regulated to transmit the bits.
The following diagram illustrates the different digital modulation schemes −
This is a method of combining more than one signal over a shared medium. Multiplexing divides the capacity of a communication channel into several logical channels, each for a data stream. The method of extracting the original data streams from the multiplexed signal is called demultiplexing.
The methods of multiplexing are as follows −