In binary frequency-shift keying (binary FSK or BFSK) carrier is
shifted between two frequencies. A convenient way of trading bandwidth
for signalling speed is to increase the spread between the
lowest and highest frequency (increasing the bandwidth) but to increase
the signalling speed by extending the number of frequencies to
a number M. Such a system is called an M-ary
frequency-shift keying system.
Other topics in our resources on Communications Systems related to M-ary FSK include: