The Channel decoder recovers the information bearing bits from the coded
binary stream. Error detection and possible correction is also performed by
the channel decoder.
The important parameters of coder / decoder are: Method of coding,
efficiency, error control capabilities and complexity of the circuit.
The Modulator converts the input bit stream into an electrical
waveform suitable for transmission over the communication channel.
Modulator can be effectively used to minimize the effects of channel noise,
to match the frequency spectrum of transmitted signal with channel
characteristics, to provide the capability to multiplex many signals.
The extraction of the message from the information bearing waveform
produced by the modulation is accomplished by the demodulator. The
output of the demodulator is bit stream. The important parameter is the
method of demodulation.
The Channel provides the electrical connection between the source
and destination. The different channels are: Pair of wires, Coaxial cable,
Optical fibre, Radio channel, Satellite channel or combination of any of
The communication channels have only finite Bandwidth, non-ideal
frequency response, the signal often suffers amplitude and phase distortion
as it travels over the channel. Also, the signal power decreases due to the
attenuation of the channel.
The signal is corrupted by unwanted,
unpredictable electrical signals referred to as noise.
The important parameters of the channel are Signal to Noise power
Ratio (SNR), usable bandwidth, amplitude and phase response and the
statistical properties of noise.
Advantages of Digital Communication
1. The effect of distortion, noise and interference is less in a digital
communication system. This is because the disturbance must be large
enough to change the pulse from one state to the other.