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DIGITAL RADIO GUIDE TERRESTRIAL TRANSMISSION SYSTEMS - HD RADIO
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Figure 4.13: Functional Block Diagram of HD Radio System
(1) Audio Source Coding and Compression
The Audio subsystem performs the source coding and compression of the sampled
digitized Main Program Service (MPS) Audio program material. “Source coding and
compression” refers to the bit rate reduction methods, also known as data
compression, appropriate for application to the audio digital data stream. In hybrid
modes, the MPS Audio is also analog modulated directly onto the carrier for
reception by conventional analog receivers. Several categories of data may also be
transmitted on the digital signal including station identification, messages related to
the audio program material, and general data services.
(2) Transport and Service Multiplex
“Transport and service multiplex” refers to the means of dividing the digital data
stream in “packets” of information, the means of uniquely identifying each packet or
packet type (data or audio), and the appropriate methods of multiplexing audio data
stream packets and data stream packets into a single information stream. The
transport protocols have been developed specifically to support data and audio
transmission in the AM and FM radio bands. The IBOC transport is modelled
loosely on ISO 7498 standard.