Digital radio


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. Common examples include Digital Audio Broadcasting and HD Radio. This should not be confused with Internet radio which also is digital but not transmitted by radio waves in the radio spectrum. It is the newer counterpart to older, analog communications or broadcasting, which include the use of FM and AM.

Types

In digital broadcasting systems, the analog audio signal is digitized, compressed using an audio coding format such as AAC+ 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 is still more popular and listening to radio over IP 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 and Digital Radio Mondiale, the Japanese ISDB-T and the in-band on-channel technique used in the US and Arab world and branded as HD Radio. - 5G Broadcast is a joint digital terrestrial broadcasting platform for radio and television under development in the UHF band being tested in 20 countries for more than five years.
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 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.

One-way (broadcasting) systems

Broadcast standards

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 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, 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 1998 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. 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, as well as Sweden.
The two pan-European associations for community radio Community Media Forum Europe and AMARC Europe have stated to the European Commission that FM radio should be retained for local radio. In case of a future digital transition DRM+ would be the choice.
To date the following standards have been defined for one-way digital radio:

Digital audio broadcasting systems

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

Status by country

DAB adopters

, 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 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.

Australia

Australia commenced regular digital audio broadcasting using the DAB+ standard on 4 May 2009, after many years of trialling alternative systems. Normal radio services operate on the AM and FM bands, as well as four stations on digital TV channels. The services are currently operating in five state capital cities: Adelaide, Brisbane, Melbourne, Perth and Sydney, and is being trialled in Canberra and Darwin.

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, all within the province of Ontario.

Germany

In 2020, DAB+ signals cover more than 90% of Germany. A national multiplex contains three public stations by Deutschlandfunk and 12 commercial stations. In most areas, additional multiplexes with public broadcasters and regional commercial stations are available.
The first DAB station network was deployed in Bavaria since 17 October 1995 until full coverage in 1999. Other states had funded a station network but the lack of success led them to scrap the funding - the MDR switched off in 1998 already and Brandenburg declared a failure in 2004. Instead Berlin/Brandenburg began to switch to digital radio based on an audio-only DVB-T mode given the success of the DVB-T standard in the region when earlier analogue television was switched off in August 2003. During that time the DVB-H variant of the DVB family was released for transmission to mobile receivers in 2004. During 2005 most radio stations left the DAB network with only one public service broadcaster ensemble to remain in the now fully state-funded station network. At last the blocked federal funding on 15. July 2009 until economic viability of DAB broadcasting would be proven - and pointing to DVB-T as a viable alternative.
Digital radio deployment was rebooted during 2011 - a joint commission of public and private radio broadcasters decided upon "DAB+" as the new national standard in December 2010. The new station network started as planned on 1. August 2011 with 27 stations with 10 kW each giving a coverage of 70% across the nation. A single "Bundesmux" was created on band 5C as a single-frequency network on channel 5C. With the initial market success of DAB+ the contractors decided on an expansion of the digital radio station network in November 2012.