Frequency shift keying (FSK) is a modulation method that transmits digital information by changing the frequency of the carrier. Its basic principle is to use the frequency change of the carrier to transmit digital information. Specifically, FSK controls the frequency of the analog carrier signal through the baseband pulse signal so that it changes with the change of the baseband pulse. Usually, FSK uses two different frequencies f1 and f2 to represent binary "0" and "1" respectively.
Working principle
In FSK, the amplitude and phase of the carrier remain unchanged, while the frequency changes according to the change of the digital baseband signal. There are two specific implementation methods:
Analog frequency modulation method: It is realized by analog frequency modulation circuit. The phase of the generated 2FSK signal between adjacent code elements is continuously changed, which is called continuous phase FSK (CPFSK).
Keying method: Two different independent frequency sources are selected through the switching circuit to output one of the two carriers f1 or f2 during each code element. The phase between adjacent code elements of the 2FSK signal generated in this way is not necessarily continuous.
Modulation and demodulation methods
There are two ways to modulate FSK signals:
Analog frequency modulation method: implemented through analog frequency modulation circuit.
Keying method: two different independent frequency sources are selected through a switching circuit.
The demodulation methods include coherent demodulation and incoherent demodulation:
Coherent demodulation: a synchronized local coherent carrier is required, which is implemented through a multiplier and a low-pass filter.
Incoherent demodulation: a linear envelope detector and a low-pass filter are used instead of the multiplier and low-pass filter in coherent demodulation. The sampling decision adopts a comparative decision method, and there is no need to set a decision threshold level.
Application scenarios
FSK is widely used in wireless communication, data transmission and other fields, such as radio broadcasting, remote control, etc. Due to its strong anti-interference ability and easy implementation, FSK performs well in fading channels, so it is widely used in some fading channels.
