Modulation
Modulation is the process of changing the amplitude, frequency, or phase of a radio frequency carrier signal (a carrier) to change with the information signal (such as voice or data). Digital modulation is the process of creating an analog signal that represents digital information.
The GSM physical radio channels uses Gaussian minimum shift keying (GMSK). GMSK is a form of two-level digital FM modulation. The radio channel has a gross data transmission rate of a GSM channel is 271 kbps.