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What is the different GMSK and GFSK?

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Rayengine

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gfsk bt

Hi,

How to interprete the GMSK and GFSK? Someone write as when BT=0.5, they are same ! Any explanation.

GMSK = Guassian Minimum Shift Keying;
GFSK = Guassian Frequency Shift Keying;

Rgs

Rayengine
 

flatulent

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gfsk fsk spectrum

The G stands for Gaussian shaped baseband data pulses. The FSK is frequency shift keying without any limit on the exact shift. For the special case of M, the shift is such that over a bit period the phase of the carrier changes by 90 degrees. The 0.5 comes from the shift being half the bit rate. A value of 0.7 produces a wider signal but one that can be demodulated at about 1.5 dB lower signal strength.

This has the special feature of making the signal spectrum decline rapidly in amplitude as the frequency gets farther from the carrier. This has the good results that the signal on the next frequency channel is not interfered with.
 

Rayengine

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application gmsk in dect

Dear flatulent,

Thanks for your reply. The question why I asked the question is for DECT system. For many publication and article, the GFSK and GMSK is mixed together without clear identification. For ETSI standard, the DECT is GFSK BT=0.5, I want to know if really GFSK (BT = 0.5) is equal to GMSK ? A spectral analysis is more helpful.
 

olive

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dect system using gmsk

Continuous phase FSK with modulation index equals to 0.5 is called MSK because phase shift is equal to pi/2 or -pi/2 every bit period. It is equivalent to differential binary PSK. With DECT for example, it happens when frequency deviation is exactly 288kHz. But DECT allows to have frequency deviation from 250kHz to 400kHz. Strictly speaking it is not MSK buf FSK.
The G stands for Gaussian Filtered. A Gaussian filter is characterised by the product of Bandwith by Symbol duration or BT. BT=0.5 for DECT, but can be different. 0.8 for GSM if my memory is correct.
 

abba

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dect gfsk bt

hey guys, whats going on????
MSK = 2 FSK
FSK = either 2 FSK or 4 FSK
GMSK = 2 FSK with Gauss filter
GFSK = 2 FSK with Gauss filter or 4 FSK with Gauss filter
 

rfsystem

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gmsk and gfsk

Olive make the point.

It should be exact B*T=0.5 or n*Pi()/2

The difference is that GMSK allows easier coherent demodulation. So you could allow about 3dB less S/N for the same BER.
 

Zardosht

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Hi every body.

I need close form of probability of error GFSK. I would appreciate if any one help me.

best regards
 

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