In-band On-channel - IBOC Versus DAB

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 part of 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 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. 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). 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.