Modulation is fundamental to electronic communications. The modulating signal might be analog in nature (voice or music) or digital bit streams. Most modern communication systems are digital, using discrete levels of amplitude or phase to represent the data being transmitted. The more unique conditions that can reliably travel from a transmitter to a receiver, the more data you can send in a given period of time.
Quadrature modulation is widely used in digital communications systems up to and including 5G.
The basic idea behind modulation is to control one or more parameters of an RF carrier by the modulating signal. Mathematically, we can express this as shown above.
Source: Quadrature modulation: The signal behind digital communications | EDN