DAB+

Digital radio is the use of digital technology to transmit or receive across the radio spectrum. Digital transmission by radio waves includes digital broadcasting, and especially digital audio radio services.

Types

In digital broadcasting systems, the analog audio signal is digitized, compressed using an audio coding format such as AAC+ ( MDCT) or MP2, and transmitted using a digital modulation scheme. The aim is to increase the number of radio programs in a given spectrum, to improve the audio quality, to eliminate fading problems in mobile environments, to allow additional datacasting services, and to decrease the transmission power or the number of transmitters required to cover a region. However, analog radio (AM and FM) is still more popular and listening to radio over IP (Internet Protocol) is growing in popularity.

In 2012 four digital wireless radio systems are recognized by the International Telecommunication Union: the two European systems Digital Audio Broadcasting (DAB) and Digital Radio Mondiale (DRM), the Japanese ISDB-T and the in-band on-channel technique used in the US and Arab world and branded as HD Radio.

An older definition, still used in communication engineering literature, is wireless digital transmission technologies, i.e. microwave and radio frequency communication standards where analog information signals as well as digital data are carried by a digital signal, by means of a digital modulation method. This definition includes broadcasting systems such as digital TV and digital radio broadcasting, but also two-way digital radio standards such as the second generation ( 2G) cell-phones and later, short-range communication such as digital cordless phones, wireless computer networks, digital micro-wave radio links, deep space communication systems such as communications to and from the two Voyager space probes, etc.

A less common definition is radio receiver and transmitter implementations that are based on digital signal processing, but may transmit or receive analog radio transmission standards, for example FM radio. This may reduce noise and distortion induced in the electronics. It also allows software radio implementations, where the transmission technology is changed just by selecting another piece of software. In most cases, this would however increase the energy consumption of the receiver equipment.

One-way (broadcasting) systems

Broadcast standards

Digital audio radio service standards may provide terrestrial or satellite radio service. Digital radio broadcasting systems are typically designed for handheld mobile devices, like mobile-TV systems and unlike other digital TV systems which typically require a fixed directional antenna. Some digital radio systems provide in-band on-channel (IBOC) solutions that may coexist with or simulcast with analog AM or FM transmissions, while others are designed for designated radio frequency bands. The latter allows one wideband radio signal to carry a multiplex of several radio-channels of various bitrates as well as data services and other forms of media. Some digital broadcasting systems allow single-frequency network (SFN), where all terrestrial transmitters in a region sending the same multiplex of radio programs may use the same frequency channel without self- interference problems, further improving the system spectral efficiency.

While digital broadcasting offers many potential benefits, its introduction has been hindered by a lack of global agreement on standards and many disadvantages. The DAB Eureka 147 standard for digital radio is coordinated by the World DMB Forum. This standard of digital radio technology was defined in the late 1980s, and is now being introduced in some European countries. Commercial DAB receivers began to be sold in 1999 and, by 2006, 500 million people were in the coverage area of DAB broadcasts, although by this time sales had only taken off in the UK and Denmark. In 2006 there are approximately 1,000 DAB stations in operation. There have been criticisms of the Eureka 147 standard and so a new ' DAB+' standard has been introduced.

The DRM standard has been used for several years to broadcast digitally on frequencies below 30 MHz (shortwave, mediumwave and longwave). Also there is now the extended standard DRM+, which is designed for VHF bands. Tests of DRM+ has been made in countries such as in Brazil, Germany, France, India, Sri Lanka, the UK, Slovakia, Italy (incl. the Vatican), as well as Sweden.

DRM+ is regarded as a more transparent and less costly standard than DAB+ and thus a better choice for local radio ; commercial or community broadcasters. Although DAB+ has been introduced in Australia the government concluded in 2011 that a preference for DRM and DRM+ above HD Radio could be used to supplement DAB+ services in (some) local and regional areas.

To date the following standards have been defined for one-way digital radio:

Digital audio broadcasting systems

* Eureka 147 (branded as DAB)
* DAB+
* ISDB-TSB
* Internet radio (Technically not a true Broadcast system)
* T-DMB V-Radio
* FM band in-band on-channel (FM IBOC):
** HD Radio (OFDM modulation over FM and AM band IBOC sidebands)
** FMeXtra (FM band IBOC subcarriers)
** Digital Radio Mondiale extension (DRM+) (OFDM modulation over AM band IBOC sidebands)
** Convergent Digital Radio (CDR) (OFDM modulation over FM band IBOC sidebands)
* AM band in-band on-channel (AM IBOC):
** HD Radio (AM IBOC sideband)
** Digital Radio Mondiale (branded as DRM) for the short, medium and long wave-bands
* Satellite radio:
** WorldSpace in Asia and Africa
** Sirius XM Radio in North America
** MobaHo! in Japan and the Republic of (South) Korea
* Systems also designed for digital TV:
** DMB
** DVB-H
** ISDB-T
** DTMB
* Low-bandwidth digital data broadcasting over existing FM radio:
** Radio Data System (branded as RDS)
* Radio pagers:
** FLEX
** ReFLEX
** POCSAG
** NTT

Digital television (DTV) broadcasting systems

* Digital Video Broadcasting (DVB)
* Integrated Services Digital Broadcasting (ISDB)
* Digital Multimedia Broadcasting (DMB)
* Digital Terrestrial Television (DTTV or DTT) to fixed mainly roof-top antennas:
** DVB-T (based on OFDM modulation)
** ISDB-T (based on OFDM modulation)
** ATSC (based on 8VSB modulation)
** T-DMB (based on OFDM modulation)
** Digital Terrestrial Multimedia Broadcast (DTMB) (based on OFDM modulation)
* Mobile TV reception in handheld devices:
** DVB-H (based on OFDM modulation)
** MediaFLO (based on OFDM modulation)
** DMB (based on OFDM modulation)
** Multimedia Broadcast Multicast Service (MBMS) via the GSM EDGE and UMTS cellular networks
** DVB-SH (based on OFDM modulation)
** China Multimedia Mobile Broadcasting (CMMB) (based on OFDM modulation)
* Satellite TV:
** DVB-S (for Satellite TV)
** ISDB-S
** 4DTV
** S-DMB
** MobaHo!
** Advanced Broadcasting System-Satellite (ABS-S)

See also software radio for a discussion of radios which use digital signal processing.

Status by country

DAB adopters

Digital Audio Broadcasting (DAB), also known as Eureka 147, has been adopted by around 20 countries worldwide. It is based on the MPEG-1 Audio Layer II audio coding format and this has been co-ordinated by the WorldDMB.

WorldDMB announced in November 2006 that DAB would be adopting the HE-AACv2 audio coding format, also known as eAAC+. Also being adopted are the MPEG Surround format, and stronger error correction coding called Reed–Solomon coding. The update has been named DAB+. Receivers that support the new DAB standard began being released during 2007 with firmware updated available for some older receivers.

DAB and DAB+ cannot be used for mobile TV because they do not include any video codecs. DAB related standards Digital Multimedia Broadcasting (DMB) and DAB-IP are suitable for mobile radio and TV both because they have MPEG 4 AVC and WMV9 respectively as video coding formats. However a DMB video sub-channel can easily be added to any DAB transmission - as DMB was designed from the outset to be carried on a DAB subchannel. DMB broadcasts in Korea carry conventional MPEG 1 Layer II DAB audio services alongside their DMB video services.

United States

The United States has opted for the proprietary HD Radio technology, a type of in-band on-channel (IBOC) technology. According to iBiquity, "HD Radio" is the company's trade name for its proprietary digital radio system, but the name does not imply either high definition or "hybrid digital" as it is commonly incorrectly referenced.

Transmissions use orthogonal frequency-division multiplexing, a technique which is also used for European terrestrial digital TV broadcast (DVB-T). HD Radio technology was developed and is licensed by iBiquity Digital Corporation. It is widely believed that a major reason for HD radio technology is to offer some limited digital radio services while preserving the relative "stick values" of the stations involved and to insure that new programming services will be controlled by existing licensees.

The FM digital schemes in the U.S. provide audio at rates from 96 to 128 kilobits per second (kbit/s), with auxiliary "subcarrier" transmissions at up to 64 kbit/s. The AM digital schemes have data rates of about 48 kbit/s, with auxiliary services provided at a much lower data rate. Both the FM and AM schemes use lossy compression techniques to make the best use of the limited bandwidth.

Lucent Digital Radio, USA Digital Radio (USADR), and Digital Radio Express commenced tests in 1999 of their various schemes for digital broadcast, with the expectation that they would report their results to the National Radio Systems Committee (NRSC) in December 1999.Behrens, Steve. "Field testing resumes for radio’s digital best hope." ''Current'', Aug. 16, 1999. Available at Results of these tests remain unclear, which in general describes the status of the terrestrial digital radio broadcasting effort in North America.

While traditional terrestrial radio broadcasters are trying to "go digital", most major US automobile manufacturers are promoting digital satellite radio. HD Radio technology has also made inroads in the automotive sector with factory-installed options announced by BMW, Ford, Hyundai, Jaguar, Lincoln, Mercedes, MINI, and Volvo.

Satellite radio is distinguished by its freedom from FCC censorship in the United States, its relative lack of advertising, and its ability to allow people on the road to listen to the same stations at any location in the country. Listeners must currently pay an annual or monthly subscription fee in order to access the service, and must install a separate security card in each radio or receiver they use.

Sirius Satellite Radio launched a constellation of three Sirius satellites during the course of 2000. The satellites were built by Space Systems/Loral and were launched by Russian Proton boosters. As with XM Satellite Radio, Sirius implemented a series of terrestrial ground repeaters where satellite signal would otherwise be blocked by large structures including natural structures and high-rise buildings.

XM Satellite Radio has a constellation of three satellites, two of which were launched in the spring of 2001, with one following later in 2005. The satellites are Boeing 702 comsats, and were put into orbit by Sea Launch boosters. Back-up ground transmitters ( repeaters) will be built in cities where satellite signals could be blocked by big buildings.

On February 19, 2007, Sirius Satellite Radio and XM Satellite Radio merged, to form Sirius XM Radio.

The FCC has auctioned bandwidth allocations for satellite broadcast in the S band range, around 2.3 GHz.

Terrestrial broadcasting has advantages in being free and local. Satellite radio is neither of these things; however, in the early 21st century it has grown by providing uncensored content (most notably, the crossover of Howard Stern from terrestrial radio to satellite radio) and commercial-free, all-digital music channels that offer similar radio formats to local stations.

The "HD Radio" signal of an FM broadcast station in the US has a limited listening distance from the broadcast tower site. FCC regulations currently limit the power of the digital part of the station's transmission to 10% of the existing analog power permitted the station. Even at this power level, the presence of the digital signal right next to the station's analog signal can result in older radios picking up noise due to trouble rejecting the adjacent digital signal. "There are still some concerns that HD Radio on FM will increase interference between different stations even though HD Radio at the 10% power level fits within the FCC spectral mask." HD Radio HD Radio#cite note-14.

"HD Radio" allows each existing broadcast station to add additional "channels" in the US by transmitting a digital signal on both sides of its channel, just beyond their existing analog Frequency Modulation signal. The HD Radio signal occupies the 0.1 MHz that begins 0.1 MHz above and below the carrier frequency station. For instance, if a station's analog signal's carrier frequency is 93.3 MHz, the digital signal will fill 93.1–93.2 MHz and 93.4–93.5 MHz within the FM Broadcast Band. Several digital audio streams, or "subchannels", can be carried within this single digital data stream, with the number of audio of subchannels and bandwidth allocations at the choice of the station. On the radio tuner, these will appear as (in the above case) "93.3-2", "93.3-3", and so on. The frequencies that are used do not change as more channels are added to the one radio station (93.3 MHz in the example above). Instead, a fixed total amount of bandwidth is simply reallocated across the audio streams such that each now receives less bandwidth, and therefore lower audio quality, than before.

There is no federally mandated transition to HD Radio for both FM and AM Stations. However, on October 27, 2020, the FCC approved voluntary all-digital AM operation nationwide.

Canada

Canada has begun allowing experimental HD Radio broadcasts in December 2012 and digital audio subchannels on a case-by-case basis, with the first stations in the country being CFRM-FM in Little Current, CING-FM in Hamilton, and CJSA-FM in Toronto (with a fourth, CFMS-FM

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