difference between GMSK (Gaussian Minimum shift keying) and GFSK (Gaussain frequency shift keying) I am unable to differentiate GMSK and GFSK. 
How do the modulation techniques differ in Tx?

How do their receiving techniques differ..?
With GMSK, the frequency modulation index is 0.5. With GFSK, the frequency modulation index is larger than 0.5 (the signaling tones are farther apart).
The receiving techniques used for GMSK as an FSK work for GFSK.