Editing Frequency-shift keying (section)

===Gaussian frequency-shift keying===
Rather than directly modulating the frequency with the digital data symbols, "instantaneously" changing the frequency at the beginning of each symbol period, '''Gaussian frequency-shift keying''' ('''GFSK''') filters the data pulses with a [[Gaussian filter]] to make the transitions smoother. This filter has the advantage of reducing [[sideband]] power, reducing interference with neighboring channels, at the cost of increasing [[intersymbol interference]]. It is used by [[Improved Layer 2 Protocol]], [[DECT]], [[Bluetooth]],<ref>[https://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1158106 ieeexplore.ieee.org], Sweeney, D.; "An introduction to bluetooth a standard for short range wireless networking" ''Proceedings. 15th Annual IEEE International ASIC/SOC Conference, Rochester, NY, US, 25-28 Sept. 2002'', pp. 474–475. 2002.</ref> [[Cypress WirelessUSB]], [[Nordic Semiconductor]],<ref>Nordic Semiconductor.  [http://www.nordicsemi.com/files/Product/data_sheet/Preliminary_Product_Specification_nRF24LU1P_v1_2.pdf nRF24LU1+ Preliminary Product Specification v1.2]{{webarchive |url=https://web.archive.org/web/20110220064408/http://www.nordicsemi.com/files/Product/data_sheet/Preliminary_Product_Specification_nRF24LU1P_v1_2.pdf |date=2011-02-20}}</ref> [[Texas Instruments]],<ref>[http://processors.wiki.ti.com/index.php/Category:LPRF LPRF] {{Webarchive|url=https://web.archive.org/web/20170104162432/http://processors.wiki.ti.com/index.php/Category:LPRF |date=2017-01-04 }}</ref> [[IEEE 802.15.4]], [[Z-Wave]] and [[Wavenis]] devices. For basic data rate [[Bluetooth]] the minimum deviation is 115&nbsp;kHz.

A GFSK modulator differs from a simple frequency-shift keying modulator in that before the [[baseband]] waveform (with levels −1 and +1) goes into the FSK modulator, it passed through a [[Gaussian filter]] to make the transitions smoother to limit spectral width. Gaussian filtering is a standard way to reduce 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 the pulse is changed going from −1 to +1 as −1, −0.98, −0.93, ..., +0.93, +0.98, +1, and this smoother pulse is used to determine the [[carrier frequency]], the out-of-band spectrum will be reduced.<ref>{{cite web |last1=Bhagwat |first1=Pravin |title=Bluetooth: 1.Applications, Technology and Performance |url=http://faculty.kfupm.edu.sa/coe/mayez/ps-coe541/references/Chapter11.ppt |access-date=27 May 2015 |page=21 |date=10 May 2005}}</ref>