HD Radio Tutorial
What is the typical application of the communication technology that you choose to study? Give some examples and pictures. What products use this technology?
HD Radio originally stood for ¡°Hybrid Digital¡± and is the trademark for iBiquity¡¯s in-band on-channel (IBOC) digital radio technology used by AM and FM radio stations to transmit audio and data via a digital signal in conjunction with their analog signals. It is the only system approved by the FCC for digital AM/FM broadcasts in the U.S. It is officially called NRSC-5, with the latest version as NRSC-5B. More than 1,900 stations covering approximately 84% of the U.S. are broadcasting with this technology, and more than 1,000 HD2 and HD3 multicast channels are on the air. Digital information is transmitted using orthogonal frequency-division multiplexing with an audio compression algorithm called PAC(Perceptual audio coder). However, the audio was poor quality, so in 2003 iBiquity combined it with SBR (spectral band replication) that improves audio quality at low bit rates and branded the codec to HDC (High-Definition Coding). 
What is the frequency band allocated by FCC for this technology?
The strength of NRSC-5 is that it uses the existing AM and FM alloccated frequencys. Also, the band width for the sperate stations has not been altered either. Therefore, no change was needed to any existing radio to impliment this technology. The only new requirement for the consumer would be to purchase a new radio receiver capable of tuning in the digital channels that the radio stations modulated into their broadcast signal.
AM radio operates in the medium frequency band which is 300 to 3000 kHz. The maxium audio frequency for the analog AM broadcast is approxiamatly 10kHz. This results in a maximum bandwidth of 20kHz per station. As stated previously, digital AM broadcast will operate in the same band at the same frequencies with the same bandwidth. This is shown by the signal diagrams below. The diagrams describe the different capabilities of NRSC-5 with transmitting an analog and digital hybrid signal.
AM Hybrid waveform spectrum(courtesy of iBiquity)
AM digital waveform spectrum (courtesy of iBiquity)
FM radio operates in the very high frequency range and uses frequencies from 87.5 to 108MHz usually. The maximum audio frequency for the analog FM broadcasts is approximately 15kHz. The bandwidth of a FM station is about 180kHz giving a ¡°guard¡± of about 20kHz between stations. The diagrams below show three different set-ups for NRSC-5. These are hybrid, extended hybrid and strictly digital. As stated, all the different configurations operate inside the already established standards for FM broadcasting
Hybrid waveform (courtesy of iBiquity)
Extended hybrid waveform spectrum
All-digital waveform (courtesy of iBiquity)
Who is the standard body? Where can one find the documents of the standard? Which part of the document is about physical layer?
The FCC has direct control over the allocation of the frequency spectrum used in the United States. NRSC-5 by iBiquity is the only digital standard allowed to broadcast at this time. The FCC also has the power to mandate that all radio broadcasts conform to their standards. The FCC has no plans to mandate that NRSC-5 be the only standard because this will not open up any frequency bandwidth for the FCC to sell.
What constellations (BPSK, QPSK, 8PSK, 16-QAM, etc.) are used?
The constellations used by the HD Radio are 16 QAM and 64 QAM for the AM and the FM uses QPSK and BPSK.
What multi-access and broadcast technologies are used? (TDM(A), CDM(A), FDM(A), OFDM(A), etc.) How do they work? (Multi-access, or uplink, means that multiple users send signals to the base station. Broadcast, or downlink, means that a base station sends different signals to different users.)
OFDM is used to produce the digital signals in the NRSC-5 standard. This is used to separate the partitions in the digital signal. Between the partiotion is also data for synchronization and diplay data sent from the station such as station id and song information.
Is the standardization on-going? Which companies are the major players?
iBiquity which is a merger of Lucent Digital Radio and USA Digital Radio is the sole patent holder of the HD radio standard and again, this is the only digital radio broadcast standard permitted in the United States. There are other countries using different standards such as DAB and Eureka 147. These different standards are 100% incompatibale with each other. There are, however, are many different companies supplying HD radio tuners. They are all the major player and more. Here are a slect number of manufactures.
Automotive (Aftermarket & Factory Installed)
The IBOC Handbook: understanding HD radio Technology