"HD Radio" is the proprietary trademark for iBiquity's in-band on-channel (IBOC) technology, which was selected by the Federal Communications Commission (FCC) in 2002 as a digital audio broadcasting method for the United States.[2][3] iBiquity Digital Corporation, the developer of the technology, reports that HD Radio broadcasts are available on 1800 stations.[4] According to iBiquity's website HD Radio is simply a brand name, although their earlier whitepaper documents refer to "Hybrid Digital" radio technology. [5]
The HD Radio system is officially known as NRSC-5, with the latest version being NRSC-5A.[6] Other digital radio systems include FMeXtra, Digital Radio Mondiale (DRM+), and Compatible AM-Digital (CAM-D).
Overview
Digital information is transmitted using COFDM with anaudio compression algorithm called HDC with SBR (based upon MPEG-4 HE-AAC). HD Radio equipped stations pay a one-time licensing fee for iBiquity's patents, software, and trademarks.[7] Receiver manufacturers pay a royalty.[8]
If digital signal reception is lost, the HD Radio receiver will revert to the analog signal, thereby providing seamless operation between the newer and older transmission methods. Alternatively the HD Radio can revert to a more-robust ~20 kilobit per second stream.[5] Datacasting is also possible, with metadata providing song titles or artist information.
iBiquity Digital claims that the system approaches CD quality sound and offers reduction of both interference and static;[9] however, some listeners have complained of increased interference on the AM band (see AM, below).
AM
Sending pure digital data through the approximately 20 kilohertz AM channel is roughly equivalent to sending data through two 33 kbit/s analog telephone lines, thus limiting the maximum throughput possible. By using spectral band replication the HDC+SBR codec is able to recreate sounds up to 15,000 Hz, thus achieving FM quality on the bandwidth-tight AM band.[10] The HD Radio AM hybrid mode offers two options which can carry approximately 40 or 60 kbit/s of data, but most AM-digital stations default to the more-robust 40 kbit/s mode which features redundancy (same signal broadcast twice). HD Radio also provides a pure digital mode, which lacks an analog signal for "fall back" and instead reverts to a 20 kbit/s signal during times of poor reception. The pure digital mode transmissions will stay within the AM stations channel instead of spilling into the channels next to the station transmitting "HD radio".
The AM version of HD Radio technology widens the channel to 30 KHz bandwidth (three channels), and overlaps one adjacent channel on both sides. When operating in pure digital mode, the AM-HD Radio signal fits inside a standard 20 kHz channel (20-40 kbit/s) or an extended 30 kHz channel (40-60 kbit/s), at the discretion of the station manager.[5] Some nighttime listeners have expressed concern this design harms reception of adjacent channels [11][12] with one formal complaint filed regarding the matter: WYSL owner Bob Savage against WBZ in Boston.
FM
HD Radio Transmitter
The FM hybrid digital/analog mode offers four options which can carry approximately 100, 112, 125, or 150 kbit/s of lossy data depending upon the Station Manager's power budget and/or desired range of signal. The HD Radio also provides several pure digital modes with up to 300 kbit/s bitrate, and enabling extra features like surround sound. Like AM, pure digital FM provides a "fall back" condition where it reverts to a more-robust 25 kbit/s signal.
FM stations have the option to subdivide their datastream into sub-channels (FM97-HD1, -HD2, -HD3) of varying audio quality. The multiple services are similar to the sub-channels found in ATSC-compliant Digital Television using multiplexed broadcasting. For example, some Top 40 stations have added Hot AC and Classic rock to their sub-channels to provide more variety to listeners.[13] Stations may eventually go all-digital, thus allowing as many as three full-power channels and four low-power channels (seven total). As defined by iBiquity these channels could be sub-divided into CD-quality (100 kbit/s), FM-quality (25-50 kbit/s), AM-quality (12 kbit/s), or Talk-quality (5 kbit/s) channels.[5]
Bandwidth
Currently, FM stations in the United States and Canada are licensed to carry 130 kilohertz of bandwidth, requiring approximately 260 kilohertz of spectrum. Only 15 kHz of the modulation bandwidth is used by analog Monaural audio, with the remainder used for stereo, RBDS, paging, radio reading service, rental to other customers, or as a transmitter-studio link for in-house telemetry.
In regular hybrid mode, a station has its full ± 130 kHz of analog bandwidth, and adds an extra ± 70 kHz for its digital signals, thus taking a full 400 kHz of width. FM stations also have the option to discontinue existing subcarrier services (usually at 92 kHz and 67 kHz) in order to carry extended HD Radio, though such services can be restored through use of the digital subchannels that are then made available.
The ratio of power of the analog signal to the digital signal is standardized at 100:1, devoting 1% of the total carrier power to the digital signal. The National Association of Broadcasters (NAB) is expected to request a 10 dB increase[2] in the digital signal from the FCC.[3] This equates to an increase to 10% of the total carrier power and a decrease in the analog signal from 99% to 90%. This may reduce analog coverage slightly, but results in a dramatic improvement in digital coverage.
There are still some concerns that HD Radio on FM will increase interference between different stations because HD Radio does not fit within the FCC spectral mask. An HD Radio station will not generally cause interference to any analog station within its 1 mV/m service contour, the limit above which the FCC protects most stations.
Comparison to EU's Digital Radio
FM-HD Radio versus DAB
Some European Union states have implemented Eureka-147 Digital Audio Broadcasting (DAB), with compatible radios having been available since 1999. DAB broadcasts a single station that is approximately 1500 kilohertz in width (~1000 kilobits per second). That station is then subdivided into multiple digital streams of between 9 and 12 programs. In order to implement DAB, it was necessary for the European Telecommunications organization to set aside a new range of frequencies, whereas FM-HD Radio shares its digital broadcast with the traditional 200 kilohertz-wide channels.
In the UK, Denmark, Norway and Switzerland, which are the leading countries with regard to implementing DAB, the vast majority of stereo radio stations on DAB have a lower sound-quality than FM, prompting a number of complaints.[14][15] The typical bandwidth for DAB programs is only 128 kbit/s using the older, less-robust MPEG-1 Audio Layer II (MP2) standard which requires at least double that rate to be considered near-CD quality. For comparison, the HD Radio standard assigns up to 300 kbit/s for each individual FM station, using a more-advanced MPEG-4 HE-AAC-derived standard that can provide perceived CD quality as low as 64 kbit/s.[16][17]
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,[18] 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).[19] HD Radio shares some of these same flaws (see criticisms below).
AM-HD Radio versus DRM
The European Union states are in the process of rolling-out Digital Radio Mondiale (DRM), with compatible radios already available for sale. DRM is very similar to AM-HD Radio in that each station is broadcast via a channel 20 kilohertz wide (+/-10 kHz), and the radio is hand-tuned to each individual station's location on the dial. The two standards also share the same modulation scheme (COFDM), the same compression-decompression standard (MPEG-4 AAC+), and like HD Radio.night transmission and desired robustness.
For AM stations DRM offers a growth path for broadcasters. Unfortunately DRM shares many of the same flaws as DAB and HD Radio technology: Shorter broadcast distance as compared to analog AM signal when in hybrid mode; poor reception inside vehicles and buildings; and interference with adjacent channels (in all-digital mode the signal fits inside the designated channel mask).
Criticisms
Awareness, coverage
There is low awareness amongst consumers. According to a survey dated August 8, 2007 by Bridge Ratings, when asked the question, "Would you buy an HD radio in the next two months?" only 1.0% responded "yes".[20] Some engineers have also expressed distrust or dislike of the new system.[21] Also, a survey conducted in September of 2008 saw a small percentage confused HD radio with satellite radio.
Most of the first generation HD Radio tuners have been noted as being very insensitive, making reception problematic. The HD Radio signal is 1/100th the power of a station's analog signal. In addition it has been noted that the analog section of some tuners displays poor reception capabilities compared to older non-digital models.
Proprietary and incompatible
The HD Radio system is a different digital broadcasting standard than those previously adopted in other countries. The lack of a common standard means that digital radios of one country may not work in another, and that manufacturers must develop separate products for different countries. Whereas the AAC (Advanced Audio Coding) family of codecs are publicly documented standards, the HDC codec exists only within the HD Radio system, and is an iBiquity trade secret. Similarly DRM and DAB are open specifications, while iBiquity's HD Radio specification is partly open and partly private.[25]
Reduced quality concerns
Promotion for HD Radio does not always make clear that some of its capabilities are mutually incompatible with other of its capabilities. For example, the FM system has been described as "CD quality;" however, the FM system also allows multiplexing the data stream between two or more separate programs. A program utilizing one half or less of the data stream does not attain the higher audio quality of a single program allowed the full data stream. The FCC has declared "one free over-the-air digital stream [must be] of equal or greater quality than the station’s existing analog signal."[26] (If the FCC discontinues analog simulcasting, each station will have over 300 kbit/s bandwidth available, allowing for CD or even Surround Sound-quality audio together with multiple sub-channels.)
Another such conflict arises from the extra "free" programs available today. The broadcasting industry is seeking FCC approval for "conditional access," that is, enabling the extra programs to be available only by paid subscription (on future models of HD Radio). Conditional Access will also enable special services for the blind and hearing impaired.[27] NDS, a maker of digital media encryption technology, has a deal with iBiquity to provide HD Radio with an encrypted content-delivery system called RadioGuard.[28] NDS claims that RadioGuard will "provide additional revenue-generating possibilities."
Reduced analog signal
Radio stations are licensed in the United States to broadcast at a specific effective radiated power level. Adding HD Radio technology reduces the amount of power available for the analog portion to 99%, to make room for the 1% level digital broadcast. NPR labs recently did a study of HD radio if the power levels were increased to 10% of maximum power, and found the digital signal would increase interference on FM. However the boosted digital HD signal coverage would then exceed analog by 117% more population coverage.
Programming
Currently the HD Digital Radio Alliance, a consortium of major owners such as ABC, CBS, and ClearChannel, is acting as a liaison for stations to choose unduplicated formats for the extra channels (HD2, HD3, etc.). This is designed to provide additional choices for listeners instead of several stations all independently deciding to create the same format.
Clear Channel is selling programming of several different music genres to other competing stations, in addition to airing them on its own stations. Some stations are simulcasting their local AM or lower-power FM broadcasts on sister stations' HD2 channels. It is common practice to broadcast an older, discontinued format on HD2 channels, such as WPGB in Pittsburgh, Pennsylvania which carries its former smooth jazz format on its HD2 band. Other recent additions include introduction of air staff on HD2 stations, like KDWB's Party Zone channel in Minneapolis-Saint Paul.
Receivers
The HD Radio website has an online guide to the radios currently available.
Automotive and Home/Professional
Receivers are becoming less expensive, starting at around US$100. Manufacturers have initially focused on making car stereos. In 2008, Ford Motor Company became the first U.S. automaker to feature HD Radio tuners in its vehicles; and beginning with the 2009 model year, Ford will offer HD Radio tuners as a factory-installed option (Compatible with SYNC). [31] BMW offers Factory-Installed HD Radio on Nearly all 2008+ models. Hyundai offers factory-installed HD Radio on the Genesis 2008+ model year. Mercedes-Benz offers factory-installed HD Radio on the R320, ML320 and GL320 models (2009 model year). MINI offers factory-installed HD Radio on the Cooper, Cooper S (2008+ model year). Scion offers HD Radio on select audio systems. Volvo offers factory-installed HD Radio on the S40 T5, V50 T5, C30, C70, S80, V70, XC70 and XC90 models (2009 model year).
A short list of HD Radio automotive receiver manufacturers include Alpine Electronics, Directed Electronics, Dual, Insignia, Jensen, JVC, Kenwood, Pioneer, Sony, and Visteon.
Home and office listening equipment is currently available from several companies, in both component tuner and tabletop models, including Audio Design Associates, Boston Acoustics, Cambridge Soundworks, Day Sequerra, Denon, DICE Electronics, Directed Electronics, Insignia, Integra, Jensen, LG, Marantz, Onkyo, Polk Audio, Radiosophy, Radio Shack, Rotel, Sangean, Sony, Visteon, Yamaha.
Portable
Until now, portable HD Radio receivers have been unavailable because the chipsets needed by this technology required too much power to be practical for a battery-operated device. However, in January 2008 at the Consumer Electronics Show (CES) in Las Vegas iBiquity unveiled a prototype of a new portable receiver, roughly the size of a cigarette pack.
It is based on a new chipset developed by Samsung. Although portable, it is still a relatively power-hungry device (it will run out an average set of alkaline batteries in about two hours, according to an iBiquity engineer). But Samsung engineers at CES say a second-generation chipset due in 2009 will be about 40 percent more power efficient and then a third-generation chipset due about a year later will use even less energy. According to iBiquity, Sony and others have expressed an interest in using the first-generation chipset and that the first portable HD Radios could be on the retail market in the USA as early as Christmas 2008. The new Coby HDR-700 will be the first HD Radio to be self (battery) powered via its built in rechargeable battery pack. This will make it the first fully portable HD Radio.
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