HD Radio is a system for digital radio which uses an existing analogue FM or AM frequency. The new digital signal is broadcasted simultanious with the excisting analogue radio-signal. HD Radio also supports program associated data, such as the name of the radio station, the playlist and enhanced data services. It is also possible to use the digital radio channel for data transfer.
HD Radio makes a smooth transition from analogue radio to digital radio possible. At first, HD Radio operates in a hybrid mode of both analogue and digital transmission. Eventually, as analogue receivers are replaced by digital receivers, broadcasters are able to turn off their analogue channel and replace the spectrum with more digital program channels or data applications.
HD Radio makes use of the proprietary IBOC (In-band On-Channel) standard of iBiquity.