FrequenzShiftKeying

FrequenzShiftKeying (FSK) is a digital modulation technique in which information is conveyed by shifting the frequency of a carrier signal among discrete values. In its binary form (BFSK), two frequencies represent binary symbols, while multi-level FSK (M-FSK) uses more frequencies to encode more bits per symbol. The carrier amplitude is typically kept constant to provide a stable envelope.

Operation is straightforward: the transmitter selects one of the predefined carrier frequencies for each symbol interval according to the input data. At the receiver, the incoming signal is analyzed to determine which frequency is present, yielding the recovered data. Coherent detection uses a reference carrier, while non-coherent detection relies on energy measurements in the corresponding frequency bins.

Bandwidth and performance: The spectral width of an FSK signal depends on the data rate and the frequency separation between the tones. Wider tone separation improves error performance but increases occupied bandwidth. FSK is relatively tolerant to amplitude variations and Doppler shifts, making it suitable for RF links and noisy channels. However, it is generally less spectrally efficient than phase- or amplitude-modulation schemes at the same data rate and can require more complex receivers for high-order configurations.

Applications: FSK is widely used in low to moderate data rate communications, telemetry, and radio data links, including audio-frequency shift keying (AFSK) in some amateur radio and signaling systems, as well as in many modems and wireless protocols.

Variants and related schemes: MSK and Gaussian-filtered FSK (GFSK) are notable relatives. GFSK, used in some Bluetooth implementations, improves spectral efficiency with smoother phase transitions.