Q. Digital demodulator processes?

The functions of the receiver in Figure are the inverse of those in the transmitter. At the receiving end of a digital communication system, the digital demodulator processes the channel-corrupted transmitted waveform and reduces each waveform to a single number, which represents an estimate of the transmitted data symbol. For example, when binary modulation is used, the demodulator may process the received waveform and decide on whether the transmitted bit is a 0 or 1.The source decoder accepts the output sequence from the channel decoder, and from the knowledge of the source encoding method used, attempts to reconstruct the original signal from the source. Errors due to noise, interference, and practical system imperfections do occur. The digital-to-analog (D/A) converter reconstructs an analog message that is a close approximation to the originalmessage. The difference, or some function of the difference, between the original signal and the reconstructed signal is a measure of the distortion introduced by the digital communication system.

The remainder of this chapter deals with basic methods for analyzing and processing analog signals. A large number of building blocks in a communication system can be modeled by linear time-invariant (LTI) systems. LTI systems provide good and accurate models for a large class of communication channels. Some basic components of transmitters and receivers (such as filters, amplifiers, and equalizers) are LTI systems.