Why digital modulation is not enough for radio transmission and what are the general goals for digital modulation?

Worldwide regulation always uses FDM for separating different systems (TV, WLAN, radio, satellite …). Thus, all radio systems must modulate the digital signal onto a carrier frequency using analogue modulation. The most prominent system is the traditional radio: all music and voice use frequencies between, e.g., 10 Hz and 22 kHz. However, many different radio stations want to transmit at the same time.

Therefore, all the original signals (which use the same frequency range) must be modulated onto different carrier frequencies. Other motivations for digital modulation are antenna and medium characteristics. Important characteristics for digital modulation are spectral efficiency, power efficiency and robustness. Typical schemes are ASK, PSK, FSK.