| List ofdigital radio broadcast standards |
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| 5G Broadcast |
| ISDB standards |
| AM bandin-band on-channel (AM IBOC) |
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| FM bandin-band on-channel (FM IBOC) |
Digital Radio Mondiale (DRM;mondiale beingItalian andFrench for "worldwide") is a set ofdigital audio broadcasting technologies designed to work over the bands currently used for analogue radio broadcasting includingAM broadcasting—particularlyshortwave—andFM broadcasting. DRM is more spectrally efficient than AM and FM, allowing more stations, at higher quality, into a given amount ofbandwidth, usingxHE-AACaudio coding format. Various otherMPEG-4 codecs andOpus are also compatible, but the standard now specifiesxHE-AAC.
Digital Radio Mondiale is also the name of the internationalnon-profitconsortium that has designed the platform and is now promoting its introduction.Radio France Internationale,TéléDiffusion de France,BBC World Service,Deutsche Welle,Voice of America,Telefunken (nowTransradio) and Thomcast (nowAmpegon) took part at the formation of the DRM consortium.
The principle of DRM is that bandwidth is the limiting factor, and computer processing power is cheap; modernCPU-intensive audio compression techniques enable more efficient use of available bandwidth, at the expense of processing resources.
DRM can broadcast on frequencies below 30 MHz (long wave,medium wave andshort wave), which allow for very-long-distance signal propagation. The modes for these lower frequencies were previously known as "DRM30". In theVHF bands, the term "DRM+" was used. DRM+ is able to use available broadcast spectra between 30 and 300 MHz; generally this meansband I (47 to 68 MHz),band II (87.5 to 108 MHz) andband III (174 to 230 MHz).[1] DRM has been designed to be able to re-use portions of existing analoguetransmitter facilities such as antennas, feeders, and, especially for DRM30, the transmitters themselves, avoiding major new investment. DRM is robust against the fading and interference which often plague conventional broadcasting in these frequency ranges.
The encoding and decoding can be performed withdigital signal processing, so that a low-costembedded system with a conventional transmitter and receiver can perform the rather complex encoding and decoding.
As a digital medium, DRM can transmit other data besides the audio channels (datacasting) — as well asRDS-typemetadata orprogram-associated data asDigital Audio Broadcasting (DAB) does. DRM services can be operated in many different network configurations, from a traditionalAM one-service one-transmitter model to a multi-service (up to four) multi-transmitter model, either as asingle-frequency network (SFN) ormulti-frequency network (MFN). Hybrid operation, where the same transmitter delivers both analogue and DRM services simultaneously is also possible.
DRM incorporates technology known as Emergency Warning Features that can override other programming and activates radios which are in standby in order to receive emergency broadcasts.[2]
The technical standard is available free-of-charge from theETSI,[3] and theITU has approved its use in most of the world. Approval forITU region 2 is pending amendments to existing international agreements. The inaugural broadcast took place on June 16, 2003, inGeneva,Switzerland, at the ITU'sWorld Radio Conference.
Current broadcasters includeAkashvani (formerly All India Radio),BBC World Service,funklust (formerly known as BitXpress),Radio Exterior de España,Radio New Zealand International,Vatican Radio,Radio Romania International and Radio Kuwait.[4]
Until now[when?] DRM receivers have typically used apersonal computer. A few manufacturers have introduced DRM receivers which have thus far remained niche products due to limited choice of broadcasts. It is expected that the transition of national broadcasters to digital services on DRM, notably All India Radio, will stimulate the production of a new generation of affordable, and efficient receivers.
Chengdu NewStar Electronics is offering the DR111 from May 2012 on which meets the minimum requirements for DRM receivers specified by the DRM consortium and is sold worldwide.[5]
The General Overseas Service ofAkashvani broadcasts daily in DRM to Western Europe on 9.95 MHz at 17:45 to 22:30 UTC.[6]All India Radio is in the process of replacing and refurbishing many of its domestic AM transmitters with DRM. The project which began in 2012 is scheduled to complete during 2015.[7]
The British Broadcasting CorporationBBC has trialled the technology in theUnited Kingdom by broadcastingBBC Radio Devon in the Plymouth area in theMF band. The trial lasted for a year (April 2007 – April 2008).[8] TheBBC also trialed DRM+ in theFM band in 2010 from theCraigkelly transmitting station inFife, Scotland, over an area which included the city ofEdinburgh. In this trial, a 10 kW (ERP) FM transmitter was replaced with a 1 kW DRM+ transmitter in two different modes, and coverage compared with FM.[9] Digital Radio Mondiale was included in the 2007Ofcom consultation on the future of radio in theUnited Kingdom for the AMmedium wave band.[10]
RTÉ has also run single and multiple programme overnight tests during a similar period on the 252 kHzLW transmitter inTrim,County Meath, Ireland which was upgraded to support DRM afterAtlantic 252 closed.
The Fraunhofer Institute for integrated circuits IIS offers a package for software-defined radios which can be licensed to radio manufacturers.Software package for car radios with DRM – Digital Radio Mondiale
The DRM standard is not permitted in the US on the mediumwave or the VHF bands since theFCC acceptedHD Radio as standard for these bands. However, the shortwave band is not blocked, but is not used regularly.[11]
On 28 September 2006, theAustralian spectrum regulator, theAustralian Communications and Media Authority, announced that it had "placed an embargo on frequency bands potentially suitable for use by broadcasting services using Digital Radio Mondiale until spectrum planning can be completed" "those bands being "5,950–6,200; 7,100–7,300; 9,500–9,900; 11,650–12,050; 13,600–13,800; 15,100–15,600; 17,550–17,900; 21,450–21,850 and 25,670–26,100 kHz.[12]
Since 2005, theUnited StatesFederal Communications Commission states in47 CFR73.758 that: "For digitally modulated emissions, the Digital Radio Mondiale (DRM) standard shall be employed." Part 73, section 758 is forHF broadcasting only.
Useful bitrates for DRM30 range from 6.1 kbit/s (Mode D) to 34.8 kbit/s (Mode A) for a 10 kHz bandwidth (±5 kHz around the central frequency). It is possible to achieve bit rates up to 72 kbit/s (Mode A) by using a standard 20 kHz (±10 kHz) wide channel.[13] (For comparison, pure digitalHD Radio can broadcast 20 kbit/s using channels 10 kHz wide and up to 60 kbit/s using 20 kHz channels.)[14] Useful bitrate depends also on other parameters, such as:
When DRM was originally designed, it was clear that the most robust modes offered insufficient capacity for the then state-of-the-art audio coding formatMPEG-4HE-AAC (High Efficiency Advanced Audio Coding). Therefore, the standard launched with a choice of three different audio coding systems (source coding) depending on the bitrate:
However, with the development ofMPEG-4xHE-AAC, which is an implementation of MPEGUnified Speech and Audio Coding, the DRM standard was updated and the two speech-only coding formats, CELP and HVXC, were replaced. USAC is designed to combine the properties of a speech and a general audio coding according to bandwidth constraints and so is able to handle all kinds of programme material. Given that there were few CELP and HVXC broadcasts on-air, the decision to drop the speech-only coding formats has passed without issue.
Many broadcasters still use theHE-AAC coding format because it still offers an acceptable audio quality at bitrates above about 15 kbit/s. However, it is anticipated that in future, most broadcasters will adoptxHE-AAC.
DRM30, unlike HD Radio on the medium wave, allows multiprogramming.
DRM broadcasting can be done using a choice of different bandwidths:
The modulation used for DRM is coded orthogonal frequency division multiplexing (COFDM), where every carrier is modulated with quadrature amplitude modulation (QAM) with a selectable error coding.
The choice of transmission parameters depends on signal robustness wanted and propagation conditions. Transmission signal is affected by noise, interference, multipath wave propagation andDoppler effect.
It is possible to choose among several error coding schemes and several modulation patterns: 64-QAM, 16-QAM and 4-QAM. OFDM modulation has some parameters that must be adjusted depending on propagation conditions. This is the carrier spacing which will determine the robustness against Doppler effect (which cause frequencies offsets, spread: Doppler spread) and OFDM guard interval which determine robustness against multipath propagation (which cause delay offsets, spread: delay spread). The DRM consortium has determined four different profiles corresponding to typical propagation conditions:
The trade-off between these profiles stands between robustness, resistance in regards to propagation conditions and useful bit rates for the service. This table presents some values depending on these profiles. The larger the carrier spacing, the more the system is resistant to Doppler effect (Doppler spread). The larger the guard interval, the greater the resistance to long multipath propagation errors (delay spread).
The resulting low-bit rate digital information ismodulated usingCOFDM. It can run insimulcast mode by switching between DRM and AM, and it is also prepared for linking to other alternatives (e.g.,DAB or FM services).
DRM has been tested successfully onshortwave,mediumwave (with 9 as well as 10kHzchannel spacing) andlongwave.
| Mode | OFDM carrier spacing (Hz) | Number of carriers | Symbol length (ms) | Guard interval length (ms) | Nb symbols per frame | |||
|---|---|---|---|---|---|---|---|---|
| 9 kHz | 10 kHz | 18 kHz | 20 kHz | |||||
| A | 41.66 | 204 | 228 | 412 | 460 | 26.66 | 2.66 | 15 |
| B | 46.88 | 182 | 206 | 366 | 410 | 26.66 | 5.33 | 15 |
| C | 68.18 | - | 138 | - | 280 | 20.00 | 5.33 | 20 |
| D | 107.14 | - | 88 | - | 178 | 16.66 | 7.33 | 24 |
There is also a lower bandwidth two-way communication version of DRM as a replacement for SSB communications on HF[16] - note that it isnot compatible with the official DRM specification. It may be possible in some future time for the 4.5 kHz bandwidth DRM version used by the Amateur Radio community to be merged with the existing DRM specification.
The Dream software will receive the commercial versions and also limited transmission mode using the FAAC AAC encoder.
Error coding can be chosen to be more or less robust.
This table shows an example of useful bitrates depending on protection classes:
| Protection class | A (9 kHz) | B (9 kHz) | B (10 kHz) | C (10 kHz) | D (10 kHz) | |||
|---|---|---|---|---|---|---|---|---|
| 64-QAM | 16-QAM | 16-QAM | 64-QAM | 16-QAM | 64-QAM | 16-QAM | 64-QAM | |
| 0 | 19.6 | 7.6 | 8.7 | 17.4 | 6.8 | 13.7 | 4.5 | 9.1 |
| 1 | 23.5 | 10.2 | 11.6 | 20.9 | 9.1 | 16.4 | 6.0 | 10.9 |
| 2 | 27.8 | - | - | 24.7 | - | 19.4 | - | 12.9 |
| 3 | 30.8 | - | - | 27.4 | - | 21.5 | - | 14.3 |
The lower the protection class the higher the level of error correction.
While the initial DRM standard covered the broadcasting bands below 30 MHz, the DRM consortium voted in March 2005 to begin the process of extending the system to theVHF bands up to 108 MHz.[17]
On 31 August 2009, DRM+ (Mode E) became an official broadcasting standard with the publication of the technical specification by theEuropean Telecommunications Standards Institute; this is effectively a new release of the whole DRM spec with the additional mode permitting operation above 30 MHz up to 174 MHz.[18]
Wider bandwidth channels are used, which allows radio stations to use higher bit rates, thus providing higher audio quality. A 100 kHz DRM+ channel has sufficient capacity to carry one low-definition 0.7 megabit/s wide mobile TV channel: it would be feasible to distributemobile TV over DRM+ rather thanDMB orDVB-H. However, DRM+ (DRM Mode E) as designed and standardized only provides bitrates between 37.2 and 186.3 kbit/s[19][20] depending on robustness level, using 4-QAM or 16-QAM modulations and 100 kHz bandwidth.
| Mode | MSC modulation | Robustness level | bitrate [kbit/s] for 100 kHz Bandwidth |
|---|---|---|---|
| E | 4-QAM | Max | 37.2 |
| Min | 74.5 | ||
| 16-QAM | Max | 99.4 | |
| Min | 186.3 |
DRM+ has been successfully tested in all theVHF bands, and this gives the DRM system the widest frequency usage; it can be used inband I,II (FM-band) andIII. DRM+ can coexist with DAB inband III.[21] The ITU has published three recommendations on DRM+, known in the documents as Digital System G. This indicates the introduction of the full DRM system (DRM 30 and DRM+).ITU-R Rec. BS.1114 is the ITU recommendation for sound broadcasting in the frequency range 30 MHz to 3 GHz. DAB, HD-Radio and ISDB-T were already recommended in this document as Digital Systems A, C and F, respectively.
In 2011, the pan-European organisationCommunity Media Forum Europe[22] has recommended to the European Commission that DRM+ should rather be used for small scale broadcasting (local radio, community radio) than DAB/DAB+.
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