Demodulation requires the generation of a local version of the carrier of a received radio signal. This is simple with a DSB RF signal as the carrier is sent with the radio signal. DSB FM is a little different as strictly the carrier is not sent in the radio signal but the average frequency of the received signal is the carrier frequency. With all SSB schemes it is essential to create the carrier in a process called carrier recovery. This section considered carrier recovery for digitally modulated signals.
In modern radios carrier recovery is done in two stages. First a crude estimate of the carrier is generated and used to crudely demodulate the received signal. The crudely demodulated signal is then sampled to yield a digital demodulated signal. Then, for 2G and 3G radio, a fine carrier recovery procedure using a digital implementation of what has been described is used. With 4G and 5G radios the crude carrier recovery procedure is used then pilot tones transmitted along with the signal are used to develop a lowfrequency version of the carrier.