In-band on-channel (IBOC) transmits digital radio and analog radio broadcast signals simultaneously on the same frequency. The method uses additional subcarriers or sidebands to piggyback the digital information on a normal AM or FM analog signal. This eliminates any complicated extra frequency allocation issues.
IBOC allows for multiple program channels though this involves making additional bandwidth available in the modulation baseband. This involves removal of stereo on FM. In case of AM, IBOC is incompatible with analog stereo and the additional channels are limited to highly-compressed voice. IBOC is used on FM and AM and involves different methods.
Currently, two methods of IBOC broadcasting are used on FM that includes HD Radio Broadcasting and FMeXtra. HD Radio System, developed by iBiquity Digital Corporation uses sidebands beyond the normal ±100 kHz FM channel. HD Radio is one of the most renowned and widespread systems, with many channels on air in the US. FMeXtra, developed by Digital Radio Express, uses subcarriers within the existing signal and is completely compatible with RBDS (Radio Broadcast Data System) and HD Radio in hybrid mode. The system uses the aacPlus (HE-AAC) codec. DRM+ (Digital Radio Mondiale) provides up to four simultaneous data streams and allows for their transmission alongside an audio signal. They are broadcast at frequencies of up to 174 MHz.
A mediumwave HD Radio system was created by iBiquity for AM that uses injecting of digital sidebands above and below the audible portion of the analog audio on the primary carrier. It is based on the principle of AM stereo. Digital Radio Mondiale has created AM system very effectively. CAM-D is an extension of the current system that encodes the treble on very small digital sidebands not causing any interference to adjacent channels and mixes it with the analog baseband.