The name refers to the new digital signals being broadcast in the same AM or FM band (in-band), and associated with an existing radio channel (on-channel).
For even greater capacity, some existing subcarriers can be taken off the air to provide additional bandwidth in the modulation baseband.
Due to the reduced bandwidth in AM, IBOC is incompatible with analog stereo, although that is rarely implemented, and additional channels are limited to highly compressed voice such as traffic and weather.
The first, and only, digital technology approved for use on AM and FM broadcast frequencies by the Federal Communications Commission in the United States, is the proprietary HD Radio system developed by iBiquity Digital Corporation,[1] which transmits energy beyond the allotted ±100 kHz FM channel.
[2] This is the most widely used system, with approximately 1,560 stations transmitting HD radio in the US,[3] plus over 800 new multicast channels (as of Jan 2010).
There is a one-time license fee to iBiquity Digital, for the use of its intellectual property, as well as costs for new equipment which range from $50,000 to $100,000 US (2010) per station.
The system is far less expensive and less complicated to implement, needing only to be plugged into 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.
Digital Radio Mondiale allows for simultaneous transmission of multiple data streams alongside an audio signal.
[6] The HD Radio system employs use of injected digital sidebands above and below the audible portion of the analog audio on the primary carrier.
Developed by AM stereo pioneer Leonard R. 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.
However, it is not available in North America since that span is occupied by TV channels 7 to 13 and the amateur radio 1.25 meter (222 MHz) band.
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.
[1] A further concern to FM station operators 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).
Existing analog radios are not rendered obsolete and the consumer and industry may transition to digital at a rational pace.
[7] The typical bandwidth for DAB programs is only 128 kbit/s using the first generation CODEC, the less-robust MP2 standard which requires at least double that rate to be considered near-CD quality.
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.
It has led to derogatory terms such as IBAC (In-band adjacent-channel) and IBUZ (since the interference sounds like a buzz.)
The CBC began HD Radio testing in September 2006, focusing on transmissions from Toronto and Peterborough, Ontario.
[15] Use of HD Radio is now widespread in dense urban markets like Toronto, Vancouver and Ottawa, with some use on the AM band as well.
France began broadcasting an HD Radio signal in March 2006 and plans to multicast two or more channels.
Approximately six Mexican AM and FM stations are already operating with HD Radio technology along Mexico’s border area with the US.
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.
The Philippines National Telecommunications Commission finalized its rules for FM digital radio operations on November 11, 2007.
WPRM FM is the first station in San Juan, Puerto Rico (part of the US) to adopt HD Radio, in April 2005.
FM testing sponsored by Radio Sunshine and Ruoss AG began in Lucerne in April 2006.
[citation needed] Over 60 different HD Radio receivers are on sale in over 12,000 stores nationwide, including Apple, Best Buy, Target, and Wal-Mart.