M-ary transmission

An M-ary transmission is a type of digital modulation. Instead of sending one bit at a time as in binary, multiple messages, M, are sent. The binary data stream is divided into n tuples, where n = log₂ M bits. The signals can be represented as different frequencies, as in MFSK. In Mpsk, a data bit is represented by a symbol with a particular initial phase, increasing bandwidth efficiency n times. In M-ary ASK, MAM, signals have the same phase but different amplitudes, and in M-ary PSK, signals have the same amplitude but different phases. QAM uses both amplitude and phase modulations.^[1]

This type of transmission results in reduced channel bandwidth. However, sometimes, two or more quadrature carriers are used for modulation. This process is known as quadrature modulation.