In-band on-channel
In-band on-channel (IBOC) is a method of transmitting digital radio and analog radio broadcast signals 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 channels, though this means taking some existing subcarriers off the air to make additional bandwidth available. On FM, this will 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
The first, the 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, though uptake is still limited. Only 80 percent of Americans have access to HD Radio stations. It costs radio stations approximately $50,000 to $100,000 in new equipment to broadcast with the HD Radio system. There is also a one-time license fee to iBiquity Digital for the use of its intellectual property that varies around $10,000.
While the system is currently being implemented around the US (as of Nov. 2007, 1,500 stations are on the air in the US), the system is still a work in progress. If certain bugs like receiver sensitivity and digital signal range can be improved then the system looks quite promising.
FMeXtra
The other system is FMeXtra by Digital Radio Express, which instead uses subcarriers within the existing signal. This was introduced more recently, and consumer receivers are expected in 2006. The system is completely compatible with HD Radio in hybrid mode (but not in all-digital, which is not expected to be implemented for a very long time), and with RBDS. The stereo subcarrier can also be removed for greater digital bandwidth. However, it 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.
FMeXtra can control listening with conditional access and encryption, though it has been officially implemented (as of May 2007).
DRM+
Digital Radio Mondiale is in the initial stages of creating an open-source system for FM, though it may be too late to make a third system viable with two others already in place.
AM methods
HD Radio
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.
IBOC versus DAB
While Canada and most countries in Europe have chosen the Eureka 147 standard of digital audio broadcasting (DAB) for creating a digital radio service, the United States has been holding out for advancements in IBOC technology. Part of the reason is the use of the L band (1452–1492 MHz) for test-flight telemetry by the U.S. military and its contractors. This band is used in Canada for digital radio, but remains unavailable for reassignment from the NTIA in the U.S. for broadcasting. It also has somewhat of a disadvantage in that its higher frequency has radio propagation characteristics which are more line-of-sight than VHF (FM), and far more than mediumwave (AM).
The band used for terrestrial DAB in most of Europe 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.
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 some FM stations are already diplexed).[citation needed] 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 to 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.
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 DARS ]), 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).
Both AM and FM IBOC signals cause interference on adjacent stations. 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 is much less than its analog signal. In addition, tropospheric ducting and e-skip can reduce the range of the digital signal.
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. HD officially stands for "Hybrid Digital/analog" rather than "high definition", though the intended [mis]association with HDTV by consumers is obvious. As of May 2007, a limited number of 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. Use of HD Radio on AM has been limited to daytime use only because it causes noise on adjacent channels, and was not yet allowed at night due to its problems with skywave radio propagation, though the FCC lifted this with its final approval 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 these stations can be heard in North America as well.
IBOC around the world
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.
Canada
After having L-band DAB for several years, the CRTC and Canadian Broadcasting Corporation have also looked at the use of HD Radio, given its gradual progress in the neighbouring U.S.
China
In China, Hunan Broadcasting Company started FMeXtra transmissions in Changsha in April 2007, and plans to put others throughout the Hunan province. [1]
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.
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.
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.
Philippines
The first HD Radio in the Philippines was installed on November 29, 2006 on Baguio City.
Puerto Rico
WPRM FM is the first station in Puerto Rico to adopt HD Radio, which went on air in April 2005.
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 will be installed in buses.
United States
As of May 2007, HD Radio is on several hundred radio stations, with FMeXtra on at least several dozen. Several hundred stations belonging to the Idea Bank consortium will also have FMeXtra installed. [2]