Gaussian frequency-shift keying
Gaussian Frequency-Shift Keying (GFSK) is a type of Frequency Shift Keying modulation that utilizes a Gaussian filter to smooth positive/negative frequency deviations, which represent a binary 1 or 0. It is used by DECT, Bluetooth[1], Cypress WirelessUSB, Nordic Semiconductor, Texas Instruments LPRF and z-wave devices. For Bluetooth the minimum deviation is 115 kHz.
Generalization
In a GFSK modulator, everything is the same as an FSK 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 fc-fd and 1 for fc+fd, 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. [2]
The Fourier transform of a Gaussian curve results in a Gaussian curve.
References
- ^ Sweeney, D. "An introduction to bluetooth a standard for short range wireless networking" Proceedings. 15th Annual IEEE International ASIC/SOC Conference, Rochester, NY, USA, 25-28 Sept. 2002, pp. 474–475. 2002. http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1158106
- ^ www.palowireless.com "GFSK Differences & Advantages over FSK Modulation"
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