Advanced frequency shift keying(AFSK)

A famous scheme used in many wireless systems is minimum shift keying (MSK).MSK is basically BFSK without abrupt phase changes i.e it belongs to CPM schemes .In this data bits are first seperated into even and odd bits ,the duration of each bit being doubled.This scheme also uses two frequencies :f1- lower frequency and f2-- higher frequency,the higher frequency is twice that of higher frequency,f2= 2 f1.
According to this scheme ,the lower or higher frequency is chosen to generate the MSK signal:
1.If the even and the odd bit are both 0 ,then higher frequencies f2 is inverted.(i.e f2 is used with phase shift of 180 deg).
2. If the even bit is 1 ,odd bit is 0 then the lower frequency f1 is inverted .This is the case ,eg ,in the fifth to seventh columns.
3. If the even bit is 0 and the odd bit is 1 , f1 is taken without changing the phase .
4. If both bits are 1 then original f2 is taken.
A high frequency is always chosen if even and odd bits are equal.The signal is inverted if odd bit equals 0.This scheme avoids all pahse shift in resulting MSK signal.