Datacasting
The RDS/RBDS subcarrier (57 kHz) allows FM radios to display what station they are on, pick another frequency on the same network or with the same format, scroll brief messages like station slogans, news, weather, or traffic—even activate pagers or remote billboards. It can also broadcast EAS messages, and has a station "format" name ALERT to automatically trigger radios to tune in for emergency info, even if a CD is playing. While it never really caught on in North America, European stations frequently rely on this system. An upgraded version is built into digital radio.
xRDS is a system with which broadcasters can multiply the speed of data transmission in the FM channel by using further normal RDS subcarriers, shifted into the higher frequencies of the FM multiplex. The extra RDS subcarriers are placed in the upper empty part of the multiplex spectrum and carry the extra data payload. xRDS has no fixed frequencies for the additional 57 kHz carriers.
MSN Direct uses subcarriers to transmit traffic, gas prices, movie times, weather and other information to GPS navigation devices, wristwatches, and other devices. Many of the subcarriers are from stations owned by Clear Channel. The technology is known as DirectBand.
FMeXtra on FM uses dozens of small COFDM subcarriers to transmit digital radio in a fully in-band on-channel manner. Removing other analog subcarriers (such as stereo) increases the audio quality or channels available, and other non-audio metadata that can be sent along with it such as album covers, song lyrics, artist info, concert data, and more.
Read more about this topic: Subcarrier