World Broadcasting Unions Digital Radio User Manual - page 44
DIGITAL RADIO GUIDE
TERRESTRIAL TRANSMISSION SYSTEMS - HD RADIO
44
4.4
iBiquity HD Radio System
The HD Radio system developed by US-based iBiquity Digital was designed for regions
where limited spectrum prevents the allocation of new frequencies for digital broadcasting.
The HD Radio system allows broadcasters to simultaneously transmit an analogue and
digital signal without the need for additional spectrum for the digital signal. The HD Radio
system takes advantage of unused portions of the spectrum on either side of the
analogue carrier (as defined by the service frequency allocation “mask”) and implements
frequency re-use by including digital carriers in quadrature to the existing analogue
carrier. In either case, the analogue signals are in close proximity to the digital signals
and great care must be taken to prevent unwanted interference between them.
The HD Radio system is designed to work in hybrid mode (compatible analogue and
digital) as well as to migrate to an all-digital system once analogue radios have been
largely replaced in the future. See Figures 4.10, 4.11, and 4.12.
The HD Radio system offers a number of advantages for broadcasters, consumers and
regulators. The HD Radio system replicates the existing coverage patterns of each radio
station thereby retaining the existing economic value of the station. Broadcasters can
convert to digital broadcasts with a relatively modest investment and retain the vast
majority of their existing physical plant. In addition, the introduction of the digital signal in
the existing channel allows the broadcaster to retain the station’s existing dial position.
Because the system supports simulcast of the analogue and digital signals, consumers
are able to upgrade to digital over an extended period, taking into account normal
equipment replacement cycles. Regulators benefit because there is no need for
spectrum allocations or licensing of new stations. However, many countries are cautious
about IBOC technology because it has the potential in certain circumstances to cause
some degradation to existing analogue services, particular at the edge of the existing
analogue service area.
The HD Radio system offers the following features:
•
CD quality audio in the FM-band and FM quality stereo audio in the AM band.
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•
Digital coverage nearly equivalent to existing analogue coverage. In areas where the
digital signal is lost, the system automatically blends to the analogue back-up signal
to ensure coverage is never less than existing coverage.
•
Advanced coding technologies and time diversity between the analogue and digital
signals ensure a robust signal.
•
The FM system has demonstrated significant robustness in the presence of severe
multipath, and the AM system has demonstrated significant robustness in the
presence of impulse noise.
•
The FM system offers options for introducing new data services ranging from 1 to
300 kbps depending on the mode of operation.
The HD Radio system has been tested in North and South America. It is currently in
operation in approximately 250 stations throughout the United States and is expected to
be in use by approximately 650 stations by the end of 2005.
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See the Report of the National Radio Systems Committees, DAB Subcommittee Evaluation of the iBiquity Digital
Corporation System Part 1 – FM IBOC, November 29, 2001 (“FM NRSC Report”) and Part 2, AM IBOC, dated April 6,
2002 (“AM NRSC Report”).