Demodulation of Digitally Modulated Signals

• The transmitted signal in a communication signal are not received cleanly.
• At the very least, they are corrupted by noise.
• Other more complicated and cumbersome corruptions may occur as well.
• The fact that only a limited number of possible signals is used in digital communication systems enables us to recover the transmitted signal in most cases.
• We say, that digitally modulated signals are robust against noise.
• Digitally modulated signals can operate at noise levels where analog modulation fails.
• The most important factor determining the operation of a communication system is the ratio of signal strength to noise strength.
• This ratio is called the signal-to-noise-ratio or SNR.