Modulator I/Q GMSK vs GFSK

[KlaussIT]

Hello,

I heard GFSK and GMSK Modulation can be implemented using I/Q Modulator, but what is the difference ?

Thanks.

Regards.

 

[FvM]

An I/Q modulator is an universal means to upconvert baseband to passband signals. It can be used for any kind of modulation. GFSK and GMSK are however modulation methods with constant carrier level, so they don't necessarily need an I/Q modulator, they can be generated by a simple VCO.

The difference between both modulation methods is the frequency respectively phase waveform. FSK switches (which respective smooth transition) between frequencies, MSK between phases.

 

[KlaussIT]

Thanks for this answer. But I asked this because I want to implement GMSK/GFSK both using I/Q Modulator, but I didn't find a accurate paper on the subject to distinguish the difference of implementation.

Best regards.

 

[FvM]

As said, it's of course possible with I/Q modulation. I'm sure you'll find the basic definition of both methods in text books. There's also Matlab code available on the internet which should clarify the algorithms.

 

[KlaussIT]

I didn't find any kind of code, that's why I'm asking.

 

[FvM]

Can it be that we are connected to different internet worlds although we meet at Edaboard? I get many code examples by just entering "matlab gmsk" at Google.

 

[KlaussIT]

Transmitted signal over a GMSK Modulation

Hello,

I am working on GMSK Modulation/Demodulation. I have a question regarding the transmitted signal after GMSK Modulation. Transmitted signal equal to :
- s = I.*data + Q.*data
- s = cos(data.w+phi)

Thanks.

Regards.