Amplitude shift keying, Frequency Shift Keying, Binary Phase Shift Keying: Generation and Detection
Digital modulation schemes are techniques used to encode information onto a carrier signal by varying its properties according to discrete symbols. The three fundamental digital modulation techniques are Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), and Phase Shift Keying (PSK).
Amplitude Shift Keying (ASK) is the simplest form of digital modulation. In this technique, the amplitude of a carrier signal is varied according to the binary input. Typically, a carrier is transmitted for a binary '1' and turned OFF for a binary '0', a method also known as On-Off Keying (OOK). ASK was one of the earliest modulation schemes used in wireless communication systems.
In Frequency Shift Keying (FSK), digital data is represented by shifting the frequency of the carrier signal between two distinct values. For example, a higher frequency (f₁) may represent binary '1', while a lower frequency (f₂) represents binary '0'. The amplitude of the signal remains constant while only the frequency changes.
In Phase Shift Keying (PSK), the phase of the carrier signal is varied to represent digital data. In Binary Phase Shift Keying (BPSK), a binary '1' is represented by a carrier with a reference phase, while a binary '0' is represented by a carrier shifted by 180 degrees (π radians). This makes PSK more robust to noise compared to ASK.