GFSK
Encyclopedia
Gaussian Frequency-Shift Keying (GFSK) is a type of Frequency Shift Keying modulation
that uses a Gaussian filter
to smooth positive/negative frequency deviations, which represent a binary 1 or 0. It is used by DECT, Bluetooth
, Cypress WirelessUSB, Nordic Semiconductor
, Texas Instruments LPRF, z-wave
and Wavenis
devices. For basic data rate Bluetooth
the minimum deviation is 115 kHz.
modulator except that before the baseband
pulses (-1, 1) go into the FSK modulator, it is passed through a gaussian filter
to make the pulse smoother so to limit its spectral width. Gaussian filtering is one of the very standard ways for reducing the spectral width, it is called "pulse shaping
".
If we use -1 for
and 1 for 
, once when we jump from -1 to 1 or 1 to -1, the modulated waveform changes rapidly, which introduces large out-of-band spectrum. If we change the pulse going from -1 to 1 as -1, -.98, -.93 ..... .96, .99, 1, and we use this smoother pulse to modulate the carrier, the out-of-band spectrum will be reduced.
Modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
that uses a Gaussian filter
Gaussian filter
In electronics and signal processing, a Gaussian filter is a filter whose impulse response is a Gaussian function. Gaussian filters are designed to give no overshoot to a step function input while minimizing the rise and fall time. This behavior is closely connected to the fact that the Gaussian...
to smooth positive/negative frequency deviations, which represent a binary 1 or 0. It is used by DECT, Bluetooth
Bluetooth
Bluetooth is a proprietary open wireless technology standard for exchanging data over short distances from fixed and mobile devices, creating personal area networks with high levels of security...
, Cypress WirelessUSB, Nordic Semiconductor
Nordic Semiconductor
Nordic Semiconductor is a fabless semiconductor company, developing and manufacturing integrated circuits. The company specializes in wireless communication, mixed signal as well as complex digital and analogue integrated circuit design. High speed wireless communication in the 2.4 GHz ISM band,...
, Texas Instruments LPRF, z-wave
Z-Wave
Z-Wave is a proprietary wireless communications protocol designed for home automation, specifically to remote control applications in residential and light commercial environments...
and Wavenis
Wavenis
Wavenis Wireless Technology is a 2-way Wireless connectivity platform dedicated to serving M2M applications. The main requirements in today's data-centric M2M industry are quite different from broadband and hi-speed Internet connections, and generally focus on providing ways to transmit small...
devices. For basic data rate Bluetooth
Bluetooth
Bluetooth is a proprietary open wireless technology standard for exchanging data over short distances from fixed and mobile devices, creating personal area networks with high levels of security...
the minimum deviation is 115 kHz.
Generalization
In a GFSK modulator, everything is the same as an FSKFrequency-shift keying
Frequency-shift keying is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier wave. The simplest FSK is binary FSK . BFSK uses a pair of discrete frequencies to transmit binary information. With this scheme, the "1" is called...
modulator except that before the baseband
Baseband
In telecommunications and signal processing, baseband is an adjective that describes signals and systems whose range of frequencies is measured from close to 0 hertz to a cut-off frequency, a maximum bandwidth or highest signal frequency; it is sometimes used as a noun for a band of frequencies...
pulses (-1, 1) go into the FSK modulator, it is passed through a gaussian filter
Gaussian filter
In electronics and signal processing, a Gaussian filter is a filter whose impulse response is a Gaussian function. Gaussian filters are designed to give no overshoot to a step function input while minimizing the rise and fall time. This behavior is closely connected to the fact that the Gaussian...
to make the pulse smoother so to limit its spectral width. Gaussian filtering is one of the very standard ways for reducing the spectral width, it is called "pulse shaping
Pulse shaping
In digital telecommunication, pulse shaping is the process of changing the waveform of transmitted pulses. Its purpose is to make the transmitted signal better suited to the communication channel by limiting the effective bandwidth of the transmission. By filtering the transmitted pulses this way,...
".
If we use -1 for
and 1 for , once when we jump from -1 to 1 or 1 to -1, the modulated waveform changes rapidly, which introduces large out-of-band spectrum. If we change the pulse going from -1 to 1 as -1, -.98, -.93 ..... .96, .99, 1, and we use this smoother pulse to modulate the carrier, the out-of-band spectrum will be reduced.