Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
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.
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.
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.