To transmit the ditgital signal by radio wave, it is required to modulate the carrier wave.
Digital modulation method can be categorized into 3 types:
- Amplitute Shift Keying (ASK), which changes the amplitutde of the carrier wave.
- Frequency Shift Keying (FSK), which changes the frequency of the carrier wave.
- Phse Shift Keying (PSK), which changes the phse of the carrier wave.
FSK and PSK are generally used in satellite communications.