In-band on-channel (
IBOC) is a
method of transmitting
digital radio
and
analog radio broadcast signal simultaneously on the same
frequency.
By utilizing additional digital
subcarriers or
sidebands,
digital information is "
piggybacked" on a normal
AM or
FM analog signal, thus avoiding any
complicated extra
frequency
allocation issues. However, by putting extra
RF energy beyond the edge of the station's
normally-defined channel,
interference with
adjacent channel stations is increased when
using digital sidebands.
IBOC does allow for multiple program channels, though this can
entail taking some existing subcarriers off the air to make
additional
bandwidth
available in the modulation
baseband. On
FM, this could eventually mean removing
stereo. On AM, IBOC is generally
incompatible with analog stereo at all, and any
additional channels are limited to highly-compressed voice, such as
traffic and
weather.
Eventually, stations can go from
hybrid
mode (both analog and digital) to all-digital, by eliminating the
baseband
monophonic audio.
FM methods
On FM
there are currently two methods of IBOC broadcasting in use, mainly
in the United
States
.
HD Radio Broadcasting
The first, and currently only, digital technology approved for AM
and FM broadcasting by the Federal Communications Commission in the
United States, is the
HD Radio system
developed by
iBiquity Digital Corporation,
which uses sidebands beyond the normal ±100 kHz FM channel. This is
the most well-known and widespread system in use: with over 1,700
stations on the air in the US, plus over 800 new multicast channels
(as of June 2008), 83 percent of Americans have access to HD Radio
stations. There is a one-time license fee to iBiquity Digital, for
the use of its intellectual property, as well as costs for new
equipment.
FMeXtra
The other system is
FMeXtra by
Digital Radio Express, which instead
uses subcarriers within the existing signal. This was introduced
more recently. The system is completely compatible with HD Radio in
hybrid mode (but not in all-digital mode, which is not expected to
be implemented for a very long time), and with
RBDS. The stereo subcarrier can be removed to make more
space available for FMeXtra in the modulation baseband. However,
the system is not compatible with other existing subcarriers, which
are normally not used by the general public anyhow. The system is
far less expensive and less complicated to implement, needing only
to be plugged in to the existing
exciter, and requiring no licensing
fees. FMeXtra has generally all the user features of HD Radio,
including multicast capability – the ability to broadcast several
different audio programs simultaneously. It uses the aacPlus
(HE-AAC) codec.
FMeXtra can control listening with
conditional access and
encryption.
DRM+
Digital Radio Mondiale allows
for simultaneous transmission of multiple data streams alongside an
audio signal. The DRM+ standard provides bandwidths from between 35
kbit/s to 185 kbit/s and up to four simultaneous data streams,
allowing near-CD quality audio to be broadcast alongside other
multimedia content - images, video or HTML content are typical
examples.
DRM+ is a superset of the original DRM standard, allowing for
broadcasts at frequencies of up to 108 MHz (whereas DRM only
operates at up to 30 MHz). While it is not backwardly compatible
with existing FM receiver equipment, with broadcasts digitally
encoded using AAC, this ability to operate within the
internationally agreed FM spectrum of 88-108MHz makes DRM+ a viable
candidate for future adoption when countries begin to switch off
their analogue broadcasts.
AM methods
HD Radio Broadcasting
iBiquity also created a
mediumwave HD
Radio system for AM, which is the only system approved by the
Federal Communications Commission for digital AM broadcasting in
the United States. The HD Radio system employs use of injecting
digital sidebands above and below the audible portion of the analog
audio on the primary carrier. This system also phase modulates the
carrier in
quadrature and injects more
digital information on this phase-modulated portion of the carrier.
It is based on the principle of
AM stereo
where it puts a digital signal where the
C-QUAM system would put the analog stereo decoding
information.
DRM
Digital Radio Mondiale has had much more success in creating an AM
system, and one that could be much less expensive to implement than
any
proprietary HD Radio system,
although it requires new frequency. It is the only one to have been
accepted mediumwave but also
shortwave
(and possibly
longwave) by the
International
Telecommunication Union (ITU) for use in regions I and III, but
not yet in region II, the
Americas. The HD
Radio system has also been approved by International
Telecommunication Union.
CAM-D
CAM-D is yet another method, though it is more
of an extension of the current system. Developed by AM stereo
pioneer
Leonard Kahn, It encodes the
treble on very small digital sidebands which
do not cause interference to adjacent channels, and mixes it back
with the analog baseband. Unlike the other two, it is not intended
to be capable of multichannel, opting for quality over quantity.
Unlike the HD system iBiquity calls "hybrid digital" the CAM-D
system truly is a direct hybrid of both analog and digital. Some
engineers believe that CAM-D may be compatible with analog AM
stereo with the right engineering.
Critics of CAM-D point to several drawbacks: (a), being primarily
analog, the system will be just as subject to artificial
interference and noise as the current AM system; (b), there are
virtually no receivers available for the system and at present, no
major manufacturer has announced even the intention to begin
production of them; and (c), the cost of retrofitting with CAM-D is
more than that of simply buying a new, HD-ready solid state
transmitter.
IBOC Versus DAB
While the United Kingdom has chosen the Eureka 147 standard of
digital audio broadcasting (DAB) for creating a digital radio
service, the United States has selected IBOC technology for its
digital AM and FM stations. The band used for terrestrial DAB in
the UK is VHF band III, which does not suffer from L-band's
significant line-of-sight problems. However, it is not available in
North America since that span is occupied by TV channels 7 to 13.
The stations currently occupying that spectrum did not wish to give
up their space, since VHF offers several benefits over UHF:
relatively lower power, long distance propagation (up to 100 miles
(160 km) with a rooftop antenna), and a longer wavelength that is
more robust and less affected by interference. In Canada, the
Canadian Radio-television and Telecommunications Commission (CRTC)
is continuing to follow the analog standard, so the channels remain
unavailable there as well. HD Radio testing has been authorized in
Canada, as well as other countries around the world.
There was also concern that AM and FM stations' branding, using
their current frequencies, would be lost to new channel numbers,
though virtual channels such as on digital television would
eliminate this. Also, several competing stations would have to
share a transmitter that multiplexes them all into one ensemble
with the same coverage area (though many FM stations are already
diplexed in large cities such as New York).
[35866] A further concern to FM stations was
that AM stations could suddenly be in competition with the same
high audio quality, although FM would still have the advantage of
higher data rates (300 kbit/s versus 60 kbit/s in the HD Radio
standard) due to greater bandwidth (100 kHz versus 10 kHz).
The most significant advantage for IBOC is its relative ease of
implementation. Existing analog radios are not rendered obsolete
and the consumer and industry may transition to digital at a
rational pace. In addition, the technology infrastructure is in
place: most major broadcast equipment manufacturers are
implementing IBOC technology and 60+ receiver manufacturers are
selling IBOC reception devices. In the UK, Denmark, Norway and
Switzerland, which are the leading countries with regard to
implementing DAB, the first-generation
MPEG-1 Audio Layer II (MP2) codec
stereo radio stations on DAB have a lower sound-quality than FM,
prompting a number of complaints. The typical bandwidth for DAB
programs is only 128 kbit/s using the first generation CODEC,
less-robust MP2 standard which requires at least
double
that rate to be considered near-CD quality.
Other issues with DAB include "downgrading" stations from stereo to
monaural, in order to squeeze even more
channels into the limited 1000 kbit/s bandwidth, smaller coverage
of markets as compared to analog FM, radios that are overly
expensive, poor reception inside vehicles or buildings, and a
general lack of interest in DAB (only 5 million units sold in the
largest take up area of UK by mid-2007).
A new version of the Eureka-147 standard called DAB+ has been
implemented. Using the more efficient high quality MPEG-4 CODEC
called HE-AAC v2, this compression method will allow the DAB+
system to carry more channels or have better sound quality at the
same bit rate as the old DAB system. It is the new DAB+
implementation which will be under consideration for new station
designs and not the earlier DAB scheme using the MUSICAM CODEC.
This new DAB+ system was coordinated and developed by the World DAB
Forum, formed in 1997 from the old organization. It will give the
Eureka-147 system a similar quality per bit rate as the IBOC system
and hence a better sound quality than FM.
Challenges
AM IBOC in the United States still faces some serious technological
challenges of its own, including nighttime interference with other
stations. iBiquity was previously using PAC (also used at a higher
bitrate in Sirius satellite radio [see Digital Audio Radio Service
]), but in August 2003 a switch to HDC (based-upon ACC) was made to
rectify these problems. HDC has been customized for IBOC, and it is
also likely that the patent rights and royalties for every
transmitter and receiver can be retained longer by creating a more
proprietary system. Digital Radio Mondiale is also developing an
IBOC system, likely to be used worldwide with AM shortwave radio,
and possibly with broadcast AM and FM. Neither of those have been
approved yet for ITU region 2 (the Americas). The system, however,
unlike HD Radio, does not permit the existing analog signal and the
digital signal to live together in the same channel. DRM requires
an additional channel to maintain both signals.
Both AM and FM IBOC signals cause interference to adjacent-channel
stations, but not within the station’s FCC-designated
interference-free protected contours. It has led to derogatory
terms such as IBAC (In-band adjacent-channel) and IBUZ (since the
interference sounds like a buzz.) The range of a station on an HD
Radio receiver is somewhat less than its analog signal. However, in
June, 2008, a group of US broadcasters and equipment manufacturers
requested that the U.S. Federal Communications Commission (FCC)
increase the permissible FM IBOC power from 1% (currently) to a
maximum of 10% of the analog power. In addition, tropospheric
ducting and e-skip can reduce the range of the digital signal, as
well as the analog.
In-band on-channel digital radios using iBiquity's standard are
being marketed under the brand "HD Radio" to highlight the
purported quality of reception. As of June 2008, over 60 different
receiver models have been made, and stations have received blanket
(no longer individual and experimental) authorization from the U.S.
Federal Communications Commission (FCC) to transmit in a
multiplexed multichannel mode on FM. Originally, the use of HD
Radio transmission on AM was limited to daytime only, and not
allowed at night due to potential problems with skywave radio
propagation. The FCC lifted this restriction in early 2007. DRM,
however, is being used across Europe on shortwave, which is
entirely AM skywave, without issue. With the proper receiver, many
of those stations can be heard in North America as well, sans the
analog signal.
IBOC around the world
Argentina
HD Radio technology was tested in 2004 with initial trials in
Buenos Aires. Further testing of the technology began in early
2007.
Bosnia
Trial and tests of HD Radio technology began in Sarajevo in March
2007.
Brazil
HD Radio transmission in Brazil was started on September 26, 2005.
The radio stations that use IBOC HD in Brazil are Radio
Bandeirantes, Radio Globo, and RBS Group. A total of six stations –
one FM and one AM from each group – are now transmitting in HD
Radio. KISS FM in São Paulo is the first HD Radio station in
Brazil. A total of 24 stations are broadcasting in Brazil as of
June, 2008. A joint study by the government (ANATEL) and
broadcasters’ associations (ABERT, AESP) is completed and awaiting
government action to regulate HD Radio broadcasting in
Brazil.
Canada
After having
L-band DAB for several years,
the
Canadian
Radio-Television and Telecommunications Commission (CRTC) and
Canadian Broadcasting
Corporation {CBC) have also looked at the use of HD Radio,
given its gradual progress in the neighbouring U.S.
The CBC began HD Radio
testing in September 2006, focusing on transmissions from Toronto
and Peterborough,
Ontario
. The CRTC has since revised its policy on
digital radio to allow HD Radio operations pursuant to Public
Notice CRTC 2006-160.
Czech Republic
Initial testing of the HD Radio system commenced in Prague in
February 2007.
China
In China, Hunan Broadcasting Company started FMeXtra transmissions
in Changsha in April 2007, and plans to put others throughout the
Hunan province. [1] SARFT (State Administration for Radio, Film and
Television) is currently testing HD Radio in Beijing in
contemplation for acceptance in that country.
Colombia
Caracol Radio began testing of the HD Radio technology in both the
AM and FM bands in early 2008.
Europe
In September 2007 the European HD Radio Alliance (EHDRA) was formed
by broadcasters and other interested groups to promote the adoption
of HD Radio technology by European broadcasters, regulators and
standards organizations.
France
France began broadcasting an HD Radio signal in March 2006 and
plans to multicast two or more channels. The radio stations that
use IBOC HD in France are SIRTI and NRJ Group. The owner of the
transmitter is Towercast. The frequency of IBOC HD radio is 88.2
MHz. In May 2006, The Towercast group added a single channel of
digital audio on 93.9 MHz.
Germany
Radio Regenbogen began HD Radio operations on 102.8 MHz in
Heidelberg on December 3, 2007 pursuant to government testing
authority.
Indonesia
Forum Radio Jaringan Indonesia had tested IBOC HD transmission from
March 2006 to May 2006. The IBOC HD station in Jakarta was Delta FM
(99.1 MHz). In April 2006, Radio Sangkakala (in Surabaya), the
first AM HD radio station in Asia, went on the air on 1062
kHz.
Jamaica
Radio Jamaica began operating full time with both HD Radio AM and
FM signals in the city of Kingston in 2008.
Mexico
All Mexican radio stations
within 320 km
of the U.S. border are allowed to transmit their programs on
the AM and FM bands utilizing HD Radio technology. Approximately
six Mexican AM and FM stations are already operating with HD Radio
technology along Mexico’s border area with the US. Groupo Imagen
commenced HD Radio transmissions on XHDL and XEDA in Mexico City in
June 2008.
New Zealand
HD Radio transmission in Auckland, New Zealand was started on
October 19, 2005. The frequency of IBOC HD radio is 106.1 MHz. The
transmitter is located at Skytower. Following successful testing,
the Radio Broadcasters Association (RBA) initiated a comprehensive
trial of HD Radio technology in December 2006. The aim of the trial
was to assess the coverage potential of the HD Radio system and to
make a recommendation on the suitability of the technology for
adoption.
Philippines
The first HD Radio station in the Philippines began broadcasting on
November 9, 2005. The Philippines National Telecommunications
Commission finalized its rules for FM digital radio operations on
November 11, 2007.
Poland
An HD Radio trial began in Warsaw in 2006 in order to demonstrate
the technology to local radio stations.
Puerto Rico
WPRM FM is the first station in San Juan, Puerto Rico (part of the
US) to adopt HD Radio, in April 2005. WRTU in San Juan has also
commenced broadcasting in HD Radio technology in 2007.
Switzerland
FM testing sponsored by Radio Sunshine and Ruoss AG began in
Lucerne in April 2006. HD Radio operations in Switzerland continue
and are spotlighted each year during “HD Radio Days”, an annual
gathering in Lucerne of European broadcasters and manufacturers for
the purpose of discussing the rollout of the technology in
Europe.
Thailand
HD Radio transmission in Thailand was started in April 2006. Radio
of Thailand had created a public IBOC HD radio network targeting
mass transit commuters in Thailand's capital of Bangkok. To receive
the broadcasts, more than 10,000 HD Radio receivers were installed
in buses.
Ukraine
The first FM HD Radio broadcasts in Kiev went on the air in October
2006 on two FM stations operated by the First Ukrainian Radio
Group.
Vietnam
Voice of Vietnam (VOV) commenced AM and FM HD Radio transmissions
in Hanoi in June, 2008 including multicasting, in anticipation of
making HD Radio technology a standard.
United States
As of June 2008, more than 1,700 HD Radio stations were
broadcasting 2,432 HD Radio channels. HD Radio technology is the
only digital technology approved by the FCC for digital AM and FM
broadcsting in the US. Over 60 different HD Radio receivers are on
sale in over 12,000 stores nationwide, including Apple, Best Buy,
Target, and Wal-Mart.
As of May 2007, FMeXtra is on several dozen stations. Several
hundred stations belonging to the
Idea
Bank consortium will also have
FMeXtra installed.
[35867]
See also
References
- http://www.owdjim.gen.nz/chris/radio/DRM/
- (Norwegian)
-
http://www.worlddab.org/introduction_to_digital_broadcasting/dab_plus_digital_radio
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