Digital Radio Mondiale

Logo Digital Radio Mondiale

Digital Radio Mondiale (DRM) is a narrow-band digital radio system for the distribution of up to four services in a multiplex . The system was developed for digital broadcasts on long, medium and shortwave bands in the 2000s and introduced primarily in Europe in the 2010s. However, hardly any receivers were produced, the distribution is low and as of 2019 only a few broadcasters are still broadcasting in DRM. In India , a certain coverage with DRM receivers could be achieved by 2016.

The four services of DRM are usually made up of a combination of up to three radio programs (with MPEG xHE-AAC or MPEG-4 HE-AAC v2 audio coding and associated multimedia information) and data services . DRM is an open ETSI standard and has been included in the ITU 's technical recommendations as a digital broadcast system for worldwide use.

DRM frequency ranges

DRM comprises various signal configurations for the digital distribution of broadcasts via OFDM stations in the following frequency ranges:

in the long , medium and short wave bands up to 30 MHz (called "DRM30") with the four OFDM transmission modes A, B, C and D and a bandwidth of 4.5 kHz to 20 kHz, compatible with the internationally used channel spacings ,
in VHF bands I – III from 30 MHz to 300 MHz with OFDM transmission mode E (called “DRM +”) and a bandwidth of 100 kHz; This means that DRM can be used in the VHF range (87.5–108 MHz) and, together with DAB / DAB +, also in VHF band III (174–230 MHz).

The development and global market launch of DRM is supported by the international DRM consortium , which was founded on March 4, 1998 by twenty of the world's most important international broadcasting companies and leading organizations in the media industry as well as manufacturers of receiving devices in Guangzhou / China. It has its official seat at the European Broadcasting Union (EBU) in Geneva, the project office is currently at the BBC in London.

In Germany, the German DRM Forum was founded in 2003 as an open association of interested market participants for the introduction of DRM in Germany and neighboring countries.

For several years (as of 2018) it has been shown that DRM has not established itself as a technical system. ARD, which was initially very committed to this technology through Deutsche Welle, has completely withdrawn from the DRM system.

A description of the introduction and implementation of DRM that goes beyond this article can be found in the DRM Introduction and Implementation Guide (status: Sept. 2013) of the DRM consortium.

DRM system technology

System components

The configuration of the baseband signal for the transmission of audio and data services via DRM up to the generation of the OFDM signal for transmission via a transmitter is implemented in two essential functional units: the DRM content server and the DRM modulator.

DRM content server

The DRM content server with the audio and data service encoders for a broadcast signal and the multiplexer is used to merge the content in the main service channel (MSC). In addition, the Fast Access Channel (FAC) and the Service Description Channel (SDC) are added to the multiplex signal. These two channels contain parameters for identifying the transmitted content and the transmission parameters for receiving the DRM signal. The entire multiplex signal is forwarded via the Multiplex Distribution Interface (MDI) using the so-called Distribution and Communications Protocol (DCP).

DRM modulator

The DRM modulator takes over the channel coding for the MSC, the FAC and the SDC separately with an energy dispersal and a convolutional encoder . The MSC also runs through a time interleaver. In addition, the pilot signals for the channel estimation of the OFDM signal are generated. Then the frame for the actual OFDM signal is generated, which is converted to the desired transmission frequency as an RF signal .

MDI / DCP signal feed

DRM distribution network

The DRM multiplex signal is usually compiled and configured in the studio with the DRM content server and fed to the DRM modulator at the respective transmission locations via the Multiplex Distribution Interface (MDI) with the Distribution and Communications Protocol (DCP).

The MDI / DCP signal contains the actual DRM multiplex (consisting of MSC, FAC, SDC), all information for the DRM modulator (OFDM mode, time stamp for SFN operation, network-specific information, etc.) as well as other specific information and additional error protection data. In the simplest case, the bit rate of the MDI / DCP data stream is only approx. 20-25% higher than the DRM multiplex signal and can be sent to one via narrowband transmission paths, e.g. via UDP / IP, serial lines, satellites, WAN, LAN and ISDN or several DRM modulators (e.g. in single-frequency networks) are fed in.

OFDM system parameters

In DRM, different values of the signal bandwidth and the other OFDM parameters, the QAM modulation of the multiplex baseband, the error protection classes and the time interleaving can be set. These various values are divided into five OFDM modes AE, with modes AD being defined for transmission up to 30 MHz (DRM30) and mode E for transmission in the VHF bands (DRM +).

Within the OFDM modes, there are various error protection classes that compensate for typical propagation effects such as fading , selective fading, atmospheric disturbances and disturbances from neighboring transmitters. Due to the limited data rate , in the case of critical propagation conditions u. Compromises can be found between higher error protection for good reception reliability and the associated lower net bit rate for audio and data services transmission.

Modulation and error protection
OFDM mode		MSC-QAM	Error protection	Protection level	Interleaver	Bandwidth (kHz)
A.	DRM30	64-QAM	R = 0.5 / 0.6 / 0.71 / 0.78	PL = 0/1/2/3	0.4 s / 2 s	4.5 / 5/9 / 10/18/20
B.
C.		16-QAM	R = 0.5 / 0.62	PL = 0/1
D.
E.	DRM +	16-QAM	R = 0.33 / 0.41 / 0.5 / 0.62	PL = 0/1/2/3	0.6 s	100
		4-QAM	R = 0.25 / 0.33 / 0.4 / 0.5	PL = 0/1/2/3

OFDM carrier and bandwidth
OFDM mode	Subcarrier distance [Hz]	Number of sub-carriers in bandwidth
OFDM mode	Subcarrier distance [Hz]	9 kHz	10 kHz	18 kHz	20 kHz	100 kHz
A.	41 2/3	204	228	412	460	---
B.	46 7/8	182	206	366	410	---
C.	68 2/11	---	138	---	280	---
D.	107 1/7	---	88	---	178	---
E.	444	---	---	---	---	212

OFDM symbol duration
OFDM mode	Symbol duration Tu [ms]	Guard interval Tg [ms]	Total symbol duration Ts [ms]
A.	24.00	2.66	26.66
B.	21.33	5.33	26.66
C.	14.66	5.33	20.00
D.	9.33	7.33	16.66
E.	2.25	0.25	2.5

Mode A is mainly intended for local broadcasts on the long and medium wave , in which the transmission through the bump predominates and therefore there is hardly any fading . Under certain conditions, mode A (when using 16-QAM) is also used for shortwave transmissions in order to improve the data rate and thus the sound quality.

Mode B is mainly used for shortwave transmissions with only one reflection at the ionosphere (so-called “single hop”). Mode B is also used at night in the long and medium wave range, as the sky wave is then involved in wave propagation in these bands .

Mode C can be used for shortwave transmissions over long distances. Since at these distances the waves are reflected back and forth several times between the ionosphere and the earth (so-called "multi hop"), there is an increased overlap of waves with different transit times and thus signal amplifications and signal cancellations. As a rule, mode B is still used for overseas supply, as it offers a higher data rate.

Mode D is the most insensitive to interference transmission mode and is mainly used for NVIS (Near Vertical Incidence Skywave) transmissions. This type of broadcast can be used in tropical regions. Since the waves are radiated almost vertically upwards, in addition to the already mentioned fading effects, due to the inconsistent height of the layers of air reflecting above the ground, there are also Doppler shifts.

Mode E is the only transmission mode for the VHF bands between 30 MHz and 300 MHz with a bandwidth of 100 kHz, with which DRM + can be planned in accordance with the grid of 100 kHz in the VHF band. Ensuring mobile reception at high driving speeds is also taken into account.

The following table shows the typical net bit rates in the respective OFDM modes and protection classes when using EEP (equal error protection) for the offers.

Transfer rates
OFDM mode	MSC modulation (nQAM)	Error protection	Signal bandwidth
			4.5 kHz	5 kHz	9 kHz	10 kHz	18 kHz	20 kHz	100 kHz
			Net data rate usable for offers in kbit / s (equal error protection)
A.	64	Max.	14.7	16.7	30.9	34.8	64.3	72.0
	64	min.	9.7	10.6	19.7	22.1	40.9	45.8
	16	Max.	7.8	8.8	16.4	18.4	34.1	38.2
	16	min.	6.3	7.1	13.1	14.8	27.3	30.5
B.	64	Max.	11.3	13.0	24.1	27.4	49.9	56.1
	64	min.	7.2	8.3	15.3	17.5	31.8	35.8
	16	Max.	6.0	6.9	12.8	14.6	26.5	29.8
	16	min.	4.8	5.5	10.2	11.6	21.2	23.8
C.	64	Max.				21.6		45.5
	64	min.				13.8		28.9
	16	Max.				11.5		24.1
	16	min.				9.2		19.3
D.	64	Max.				14.4		30.6
	64	min.				9.1		19.5
	16	Max.				7.6		16.2
	16	min.				6.1		13.0
E.	16	Max.							186.3
	16	min.							99.4
	4th	Max.							74.5
	4th	min.							37.2

Field strength values for network and supply planning

An important parameter for determining whether a broadcast system can be received at a certain location is the minimum useful field strength .

For DRM, it was specified that the criterion for the minimum useful field strength is a bit error rate of less than 10 ⁻⁴ in the DRM decoder of the recipient.

DRM30

For DRM30, the values for the minimum useful field strengths are specified in ITU-R BS.1615-1 (05/2011) " Planning parameters" for digital sound broadcasting at frequencies below 30 MHz .

Minimum useful field strengths for DRM30
Frequency band	Robustness mode	Bandwidth	Minimum useful field strength [dBμV / m]
			16-QAM		64-QAM
			with error protection (R)
			0.5	0.62	0.5	0.6	0.71	0.78
Long wave (ground wave propagation)	A.	4.5 kHz	39.3	41.4	44.8	46.3	48.0	49.7
Long wave (ground wave propagation)	A.	9 kHz	39.1	41.2	44.6	45.8	47.6	49.2
Medium wave (ground wave propagation)	A.	4.5 / 5 kHz	33.3	35.4	38.8	40.3	42.0	43.7
Medium wave (ground wave propagation)	A.	9/10 kHz	33.1	35.2	38.6	39.8	41.6	43.2
Medium wave (ground wave and sky wave propagation)	A.	4.5 / 5 kHz	34.3	37.2	39.7	41.1	44.2	47.4
Medium wave (ground wave and sky wave propagation)	A.	9/10 kHz	33.9	37.0	39.4	40.8	43.7	46.5
Shortwave	B.	5 kHz	19.2-22.8	22.5-28.3	25.1-28.3	27.7-30.4
Shortwave	B.	10 kHz	19.1-22.5	22.2-25.3	24.6-27.8	27.2-29.9

Radio devices are exposed to additional interference in different reception conditions in rural, extra-urban and urban environments. Interference from electrical systems (man-made noise) is of particular importance, so that the required received field strength can be up to 40 dB higher than the specified minimum useful field strengths.

DRM +

For DRM +, ITU-R BS.1660-7 (10/2015) Technical basis for planning of terrestrial digital sound broadcasting in the VHF band defines six reception situations for which the minimum useful field strengths given in the table are specified:

Fixed reception (FX): Stationary reception with a fixed receiving antenna at a height of ten meters with a location probability of 70%
Portable indoor reception (PI): Reception in the house with a radio connected to the socket with a local probability of 95%
Portable indoor reception handheld (PI-H): Reception in the house with a simple radio with integrated antenna with a location probability of 95%
Portable outdoor reception (PO): Reception outside the home with a portable, battery-operated radio with a local probability of 95%
Portable outdoor reception handheld (PO-H) : Reception outside the home with a simple radio with an integrated antenna with a local probability of 95%
Mobile reception (MO): Reception in vehicles, even at high speeds, with a location probability of 99%

Minimum useful field strengths for DRM +
Frequency range (Center frequency)	Modulation type	Error protection (R)	Minimum useful field strength [dBμV / m]
			in reception situation
			FX	PI	PI-H	PO	PO-H	MO
VHF band I (65 MHz)	4-QAM	1/3	18.15	48.91	58.06	39.71	48.26	41.11
VHF band I (65 MHz)	16-QAM	1/2	24.75	57.01	66.16	47.81	56.36	48.41
VHF band II (100 MHz)	4-QAM	1/3	17.32	50.92	61.37	40.74	50.66	42.27
VHF band II (100 MHz)	16-QAM	1/2	23.92	59.02	69.47	48.84	58.76	49.57
VHF band III (200 MHz)	4-QAM	1/3	17.26	52.52	63.89	42.38	53.30	44.13
VHF band III (200 MHz)	16-QAM	1/2	23.86	60.62	71.99	50.48	61.40	51.43

The specified minimum useful field strengths refer to a noise- limited reception situation (including man-made noise) without taking into account the influence of additional interference from other radio services that are operated in the same or adjacent radio channel. This interference from other radio services on the reception of DRM + is defined via the "Protection Ratio" (safety distance: system-dependent signal-to-noise ratio C / I between two radio services). A distinction is made as to whether DRM + interferes with another broadcast system or whether another DRM + system interferes. The signal-to-noise ratios for DRM + are specified in ITU-R BS.1660-7 (10/2015) Technical basis for planning of terrestrial digital sound broadcasting in the VHF band .

Signal transmission

DRM is broadcast as an independent digital radio signal for terrestrial broadcasting. As in today's FM and AM broadcasting, unlike in multiplex-related approaches, a single broadcast operator is provided for each broadcast signal.

Depending on the coverage task, transmitter networks can be used with transmitters that broadcast different programs on different frequencies (MFN, Multi Frequency Networks) or that supply large coverage areas with the same programs from several transmitter locations on one frequency (SFN, Single Frequency Networks).

For the transition phase from analogue to exclusively digital broadcasting, there are also various variants of simulcast transmission available.

Single frequency networks

By using OFDM with a guard interval, DRM can be distributed frequency-efficiently in single frequency networks (SFN). This operating mode is supported in all broadcast bands and operating modes.

Simulcast operation

For DRM, several forms of transmission are feasible together with analog signals (simulcast) in order to continue to guarantee AM / FM reception in a transition phase to future exclusive digital broadcasting.

The simplest simulcast variant is to switch a station alternately between DRM and analog broadcast (temporary simulcast).

A more sophisticated form of simulcast is the transmission of combined DRM / AM or DRM / FM signals in the medium wave or VHF range, which supports existing analog receivers and at the same time offers modern DRM-enabled receivers better quality, additional services and more program variety .

Adjacent channel simulcast in the MW range

DRM adjacent channel simulcast (MW)

In the medium wave range, the DRM standard provides for the DRM signal with full or half channel bandwidth to be placed next to a full AM signal with 9 or 10 kHz bandwidth (depending on the region) (adjacent-channel simulcast).

DRM-enabled medium wave transmitters are able to generate such a simulcast signal directly. The resulting extended total bandwidth between 13.5 and 20 kHz with high linearity places great demands on the bandwidth and the correct configuration of the antenna installation.

In adjacent-channel simulcast operation, part of the coordinated radiation power of the overall signal is used for the DRM signal, so that the proportion of AM power must be reduced accordingly. This reduces the AM coverage area compared to pure analogue operation of the transmitter. Depending on the configuration of the DRM signal, a transmission power of 14-16 dB below the analog signal is sufficient for comparable analog and digital coverage, with a correspondingly small reduction in the analog signal component.

In Europe, the adjacent channel simulcast has not yet been able to be used because the channel spacing is 9 kHz and the additional secondary transmission of the DRM signal is incompatible due to the interference on neighboring transmitters. In some Asian countries, e.g. B. India, the medium wave frequency assignments contain a frequency spacing of 18 kHz instead of 9 kHz or 10 kHz, so that the adjacent channel simulcast can be used over a large area there.

Single-channel simulcast in the MW range

For medium wave operation, the ETSI specification ETSI TS 102 509 V1.1.1 describes a special single channel simulcast (SCS) with which a full 9/10 kHz AM signal including a DRM signal with half the bandwidth (4, 5/5 kHz) can be transmitted in a 9/10 kHz MW channel conforming to the grid. This is achieved in that the DRM signal is transmitted unchanged in the upper half of the on-air signal, while the lower half of the signal is modified in such a way that an analog AM receiver decodes the two halves of the signal AM signal is found. Because of the transformation of the AM signal, reception can have a partially audible effect, especially with older and simply built AM receivers.

The SCS mode has not yet been introduced because the small available channel capacity of the half-width DRM signal could not ensure sufficient audio quality for the digital signal. This problem of the original SCS approach has been largely solved by the introduction of the MPEG xHE-AAC audio codec in DRM.

Since in some Asian countries a medium wave frequency allocation includes 18 kHz instead of 9 kHz or 10 kHz, the 'adjacent channel simulcast' mode is often incorrectly referred to as 'single channel simulcast'.

Simulcast in the VHF range

DRM-FM combined mode

In simulcast mode, DRM and FM signals can be emitted mutually without interference with a variable frequency spacing from 150 kHz (center-to-center) and a lower DRM power than the FM signal. With the same performance as an FM signal, DRM achieves a much greater range. Therefore, the lower DRM performance is sufficient to obtain the same range as the FM signal. Since the DRM and FM signals are independent transmission signals, the transmission power and precise frequency positioning of the DRM signal can be flexibly adapted to the requirements of the service area.

The DRM-FM simulcast signal can be generated with a single DRM-FM exciter. In this functional unit, the DRM and FM baseband signals are first generated separately and then merged into an overall signal that is converted to the intended VHF frequency. After a power boost, the signal is emitted via the antenna.

Instead, it is also possible to work with two independent transmitters, with both signals being brought together via a combiner on the antenna feed line (antenna combining). The advantage of this simulcast approach is that an existing analog FM transmitter can continue to be operated without modifications and at its most cost-effective operating point, while in addition to the combiner itself, only a DRM transmitter with low power needs to be added.

Content

Radio / audio

In DRM, either MPEG xHE-AAC or its predecessor MPEG HE-AACv2 are used as the codec for audio signals . xHE-AAC was added to the DRM standard with the standardization by MPEG and ISO and replaces the earlier pure voice codecs. It guarantees both good voice and music quality from a transmission rate of 6 kbit / s. By using xHE-AAC, a significantly better audio quality can be achieved than with AM broadcasting even when broadcasting via short, medium and long wave, despite the very narrow HF bandwidth of 4.5 kHz and above .

For example, xHE-AAC allows the transmission of stereo programs even in the very robust configurations for international shortwave coverage or the transmission of several radio programs with additional services in a single medium wave channel. The same applies to the VHF range or VHF band III, in which a single DRM signal can transmit up to 3 high-quality stereo radio programs with additional services.

Data services

Value-added services for the user

Program description: The service ID, the program name, the program type and the program language as well as the country of origin for international broadcasts are transmitted in DRM as information accompanying the program.

Text messages: Similar to radio text in RDS or dynamic labels in DAB, information about the current title and artist, the current program, program information, news ticker, etc. can be transmitted (DRM text messages).

Journaline: The text-based news service NewsService Journaline, developed for DRM and DAB , enables menu-based topic processing, so that, for example, current news, sports results, information about the station or program or regional traffic information can be specifically accessed. The service is optimized so that it can also be used decoded on simple radios or in car radios.

Service and program information (SPI) (formerly: Electronic Program Guide , EPG): Similar to DVB and DAB, SPI can be offered via DRM.

Slideshows: PNG or JPG graphics can be transmitted as slideshows, which are displayed by DRM radios with a graphic display and sufficient memory. Similar to text messages, the update interval for the images is specified by the broadcaster.

Extended signaling options

Time / Date: The current time and date are transmitted via DRM, including the local time offset for regional and local DRM broadcasts.

Automatic Frequency Switching (AFS): In multi-frequency transmitter networks, the frequency information of all transmitters that are responsible for a supply in this transmitter network is transmitted via DRM (similar to RDS in VHF radio). This enables the receiver to automatically switch to the DRM frequency that is best received. In addition to the information from your own DRM network, alternative frequencies from AM, FM and DAB networks can be transmitted so that the receiver can switch to this reception option for a program and switch back to DRM reception. For analogue LW / MW / KW transmitters, the so-called AM signaling system (AMSS) can be used as a digital additional channel for AM radio for these and other functions.

Traffic Information (TPEG / TMC): The Traffic Message Channel (TMC) for the transmission of traffic information was originally designed for RDS in FM radio and can be broadcast via DRM. The more modern successor to TMC-TPEG, the method of the Transport Protocol Experts Group, which is much more extensive in its functionality, also works via DRM.

Emergency Warning Functionality (EWF): With the help of the EWF, disaster and alarm messages can be signaled via DRM and in this way the largest possible audience in the affected area can be reached quickly and reliably. If a listener is currently listening to another program, a DRM radio automatically switches to the program with the warning messages. Depending on the manufacturer, DRM radios can also switch on automatically from standby mode in the event of an alarm. From a technical point of view, EWF is not an independent data service specification, but a combination of the standard DRM functions audio, journaline (for the provision of multilingual and detailed instructions on demand and the information of hearing-impaired users), alarm announcement and AFS signaling.

The data services and additional functions (such as EWF) supported in DRM are identical to those of the DAB standard, which enables multi-standard receivers to be implemented with little effort.

Receiver specification

The DRM consortium has developed two recipient profiles to give the recipient industry an indication of the functionalities to be implemented.

Receiver Profile 1 - Standard Radio Receiver: In this profile, a receiver with an alphanumeric display is defined, with which the AM broadcasting areas and the VHF band are received and basic DRM functions including text-based information services are to be offered.
Receiver Profile 2 - Rich Media Radio Receiver: In this profile, a receiver with a color display of at least 320 × 240 pixels is defined, whereby in addition to profile 1, slideshows, journaline and EPG must be displayed.

Normalization and standardization

ETSI

The technical specifications for DRM were published by the European Telecommunications Standards Institute (ETSI).

The main standards are:

ETSI ES 201 980 V4.1.1 (2014-01): Digital Radio Mondiale (DRM); System specification
ETSI TS 102 821 V1.4.1 (2012-10): Digital Radio Mondiale (DRM); Distribution and Communications Protocol (DCP)
ETSI TS 102 358 V1.1.1 (2005-01): Digital Radio Mondiale (DRM); Specific restrictions for the use of the Distribution and Communication Protocol (DCP)
ETSI TS 102 820 V3.1.1 (2010-12): Digital Radio Mondiale (DRM); Multiplex Distribution Interface (MDI)
ETSI TS 102 349 V4.2.1 (2016-03): Digital Radio Mondiale (DRM); Receiver Status and Control Interface (RSCI)
ETSI TS 102 386 V1.2.1 (2006-03): Digital Radio Mondiale (DRM); AM signaling system (AMSS)
ETSI TS 101 968 V1.3.1 (2009-04): Digital Radio Mondiale (DRM); Data applications directory
ETSI TS 102 509 V1.1.1 (2006-05): Digital Radio Mondiale (DRM); Single Channel Simulcast (SCS)
ETSI TS 102 668 V1.1.1 (2009-04): Digital Radio Mondiale (DRM); DRM-TMC (Traffic Message Channel)
ETSI EN 302 245-1 V1.1.1 (2005-01): Electromagnetic compatibility and Radio spectrum Matters (ERM); Transmitting equipment for the Digital Radio Mondiale (DRM) broadcasting service Part 1: Technical characteristics and test methods
ETSI EN 302 245-2 V1.1.1 (2005-01): Electromagnetic compatibility and Radio spectrum Matters (ERM); Transmitting equipment for the Digital Radio Mondiale (DRM) broadcasting service Part 2: Harmonized EN under article 3.2 of the R & TTE Directive
ETSI EN 301 234 V2.1.1 (2006-05): Digital Audio Broadcasting (DAB); Multimedia Object Transfer (MOT) protocol
ETSI TS 102 979 V1.1.1 (2008-06): Digital Audio Broadcasting (DAB); Journaline; User application specification
ETSI TS 102 818 V3.1.1 (2015-01): Hybrid Digital Radio (DAB, DRM, RadioDNS); XML Specification for Service and Program Information (SPI)
ETSI TS 102 371 V3.1.1 (2015-01): Digital Audio Broadcasting (DAB); Digital Radio Mondiale (DRM); Transportation and Binary Encoding Specification for Service and Program Information (SPI)

ITU

Every radio application and every transmission system must be approved at international level by the International Telecommunication Union (ITU). The specifications are published in the so-called Recommendations of the ITU.

The following ITU recommendations are relevant for DRM:

For DRM30:

ITU-R BS.1514-2 (03/2011) System for digital sound broadcasting in the broadcasting bands below 30 MHz
ITU-R BS.1615-1 (05/2011) “Planning parameters” for digital sound broadcasting at frequencies below 30 MHz

For DRM +:

ITU-R BS.1114-9 (06/2015) Systems for terrestrial digital sound broadcasting to vehicular, portable and fixed receivers in the frequency range 30-3000 MHz
ITU-R BS.1660-7 (10/2015) Technical basis for planning of terrestrial digital sound broadcasting in the VHF band
Report ITU-R BS.2214-1 (07/2015) Planning parameters for terrestrial digital sound broadcasting systems in VHF bands

For DRM overall:

ITU-R BS.1894 (05/2011) Digital radio broadcast service, captioned radio
ITU report BT.2299-1 (07/2015) Broadcasting for public warning, disaster mitigation and relief

ECC

Within the Electronic Communications Committee (ECC) of the CEPT, two reports were adopted in April 2012 that deal with the use of digital radio systems in Europe:

ECC Report 177 Possibilities for Future Terrestrial Delivery of Audio Broadcasting Services , with statements on the future terrestrial broadcasting of radio, in which the use of DRM (DRM30 and DRM + up to VHF band III) is described.

Technical appendix to the ECC report 141 Future Possibilities for the Digitalization of Band II (87.5-108 MHz) , in which the digital radio systems proposed for use in the VHF band are described with their technical characteristics. These are DRM (open European system in Mode E, DRM +), HD Radio (US system) and RAVIS (Russian system). Essentially, the questions of the compatibility of these systems with the existing analog FM radio and its protection are dealt with.