in binary modulation for sending e.g. 1011 we need to send for pulse but when we use e.g. 4psk only send two pulse so we can get higher sending rate.
2) in binary & ASK modulation the power of transmitter is variable and it is a disadvantage.
3)binary & ASK are so sensitive to amplitude attenuation.
** 2-PSK & 2-ASK are a kind of binary schem.
i think 4psk is the best schems for simple transmitions.
if we use it instead of FSK it is so better . because FSK has sudden frequency chenges and it means more channel frequency. but in MSK the frequency chenges contnusly and its better.