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Gaussian frequency-shift keying
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,〔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〕 Cypress WirelessUSB, Nordic Semiconductor,〔Nordic Semiconductor. (nRF24LU1+ Preliminary Product Specification v1.2 )〕 Texas Instruments LPRF, Z-Wave and Wavenis devices. For basic data rate Bluetooth the minimum deviation is 115 kHz.
==Generalization==
A GFSK modulator is similar to a FSK modulator, except that before the baseband waveform (levels −1 and +1) goes into the FSK modulator, it is passed through a Gaussian filter to make the transitions smoother so to limit its spectral width. Gaussian filtering is a standard way for reducing spectral width; it is called "pulse shaping" in this application.
In ordinary non-filtered FSK, at a 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 ..... +.93, +.98, +1, and we use this smoother pulse to determine the carrier frequency, the out-of-band spectrum will be reduced.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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