HD Radio is iBiquity's brand of digital radio technology for transmission and reception of sound that has been digitized and compressed. The Federal Communications Commission selected HD Radio as the standard for local area broadcast of signals within the United States. It offers multiple programs on one channel and works on the same frequencies allocated to analog (FM and AM) radio stations. Supporters claim CD quality sound and reduced interference. Although the acronym HD has come to mean "high-definition" in reference to HDTV, the "HD" in HD Radio is a trademark (although Hybrid digital technology is used).

1. Stations bundle analog and digital audio signals (with textual data, such as artist and song information, weather and traffic, and more).
   
   
2. The digital signal layer is compressed using iBiquity's HDC compression technology.
   
   
3. The combined analog and digital signals are transmitted.
   
   
4. The most common form of interference, multipath distortion, occurs when part of a signal bounces off an object and arrives at the receiver at a different time than the main signal. HD Radio receivers are designed to sort through the reflected signals and reduce static, hiss, pops and fades.
   
   
5. The signal will be compatible with HD Radio receivers and analog radios but the analog radios can only hear the analog sound.
   

HD Radio is a digital radio standard developed by iBiquity Digital and recognized by the U.S. Federal Communications Commission (FCC). It works the same way that traditional analog transmits, except that the audio id digital formatted and transmitted as a continuous digital data stream in addition to the analog waveform signal. On the broadcast end, audio is digitally compressed and broadcast by a transmitter designed specifically for HD Radio. Audio is also transmitted in its analog form, as usual. The radio station send out the analog and digital signals on the same broadcast frequency, along with the signals for the text data. On the listener end, the signals are received and decoded. An HD Radio tuner picks up the digital radio transmission with its accompanying text. Older analog receivers continue to pick up the analog broadcasters. Listeners can continue to enjoy their favorite stations on today’s analog receivers as well as on the new digital HD Radio receivers.

Item	Description
Frequency	FM : 87.5MHz ~ 107.9MHz AM : 530KHz ~ 1710KHz
Multicast	Up to 8channel in One frequency
AUDIO	FM : clear (CD quality) AM : Analog FM quality
Data Service	Song title, Album, Genre etc. Station Name(Long, short) Traffic, Stock (Future service)
Fare	Free service

HD Radio have two mode depends on the band usage; Hybrid mode and All Digital mode. Hybrid mode broadcast the Analog signal in main band and Digital signal in side band. The Digital signal level keeps the FCC spectrum emission guide line. All digital mode sends only the HD radio signal and the user who has analog receiver can’t listen this program.

[Figure 2. FM Hybrid Signal]	[Figure 3. FM All Digital Signal]
[Figure 4. AM Hybrid Signal]	[Figure 5. AM All Digital Signal]

1. FM Multicasting - the ability to broadcast multiple program streams over a single FM frequency.
2. (e.g. 97.7-1, 97.7-2, etc.)
3. Static-free, crystal-clear reception.
4. FM sounds as sensational as CDs.
5. AM sounds as rich as analog FM stereo.
6. A variety of "data services," including text-based information - artist name, song title, weather alerts, school closings, etc.
　scrolled across your receiver display.
7. Digital broadcasts in the same frequencies as analog broadcasts; listeners do not need to learn a new station number and
　today’s stations remain at their current place on the dial.
8. Local content .
9. Free.
10. Future functions.