DRM

1. What is the difference between 'DRM', 'DRM30' and 'DRM+', and what role does the 'DRM Consortium' play?

DRM (Digital Radio Mondiale) is the overall name of the system for digital radio broadcasting, typically carrying one service per frequency. The DRM system is standardized by ETSI (www.etsi.org) as ETSI ES 201 980 "Digital Radio Mondiale (DRM); System specification".
The DRM system operates over a wide range of broadcast frequencies and therefore has different transmission parameters designed to deal with the conditions experienced in these bands. Although the applications carried by the DRM system, namely audio and data services, are the same for the whole DRM system, the technical parameters essentially fall into two categories according to the transmission frequency of the broadcast:
DRM30 is used for transmissions using the broadcast frequencies below 30 MHz (i.e. long, medium and short wave) with a channel bandwidth between 4.5 and 20 kHz; DRM+ is used for transmissions using the broadcast frequencies above 30 MHz (i.e. VHF band I, band II FM) with a channel bandwidth of 100 kHz.
'DRM30' and 'DRM+' are therefore terms used when it is necessary to distinguish between the two sets of technical parameters.
The DRM Consortium is a not-for-profit organization which designed the DRM system and which promotes the adoption of the DRM system by regulators, broadcasters and receiver manufacturers worldwide. Members include broadcasters, network operators, regulatory bodies, transmitter equipment manufacturers, receiver and chipset manufacturers, and research institutes. The DRM Consortium is an information exchange forum open for all interested parties to join. Its homepage can be found at www.drm.org.

2. When will DRM Receivers be available and what will they cost?

A small number of receiver models for the DRM30 system are available now. At the moment, manufacturing volumes are low and prices reflect this. The ‘know how’ and the chip sets exist and so receivers could be put into volume production quite easily. Receiver chip sets supporting both DRM30 and DRM+ are available or have been announced from various major chipset vendors.
The cost, and hence the retail price, of receivers is highly dependent on the size of the market and the size of production runs. Large broadcasting organisations and major countries like India and Russia with large potential audiences are committed to the introduction of DRM services and it is to be expected that this will open the market for low-cost receivers.

3. Will I need a new receiver for DRM and what improvements in quality and service should I expect from it?

Yes, to receive DRM broadcasts a receiver with DRM capability is required.
DRM30 offers a significant improvement in the audio quality currently associated with the AM (long, medium and short wave) signals that it is intended to replace. DRM+ provides a clear and undisturbed audio quality. DRM transmissions can also provide 5.1 surround sound with full stereo receiver compatibility.
Additionally, DRM offers much easier tuning, with the listener simply selecting what he wants to listen to by its station name – frequencies and broadcast band selection is automatically done by the receiver. This means that with DRM, it is as easy to access long range international broadcasts as it is to access local transmissions. When leaving the coverage area of a broadcast, the receiver can automatically re-tune to find the same service on an alternative frequency or even another broadcast system like AM, FM, or DAB. This offers the listener easy access to a wider choice of programming.
DRM makes more efficient use of the spectrum than analogue systems. This means that there is potential to increase the choice of listening available in any given area.
DRM includes a simple and efficient way to broadcast text. Receivers with a text screen can therefore present additional information to listeners, from descriptions of the audio content to phone numbers and how to contact the station. Receivers with bigger screens and advanced text support can present detailed background information and instructions in various languages simultaneously.
Through DRM, listeners can enjoy multimedia and data services accompanying the audio programme, like an Electronic Programme Guide (EPG) to describe the current and upcoming programmes in detail, a SlideShow of still and/or animated images, Journaline services with detailed text information for interactive access (like an electronic newspaper), and traffic information.
Taking all these factors together, a DRM receiver offers the listener a much wider range of programming with enhanced audio performance and multimedia services. The DRM Consortium has developed a detailed list of functionality that should be included in DRM receivers in two classes - standard receivers and multimedia receivers. These so called receiver profiles are available on the DRM Consortium website www.drm.org.

4. Will Broadcasters need to buy new transmitters to handle DRM broadcasts?

For a considerable time, several test transmissions and small number of service transmissions have been ‘on the air’ using the DRM30 system. These have all used existing analogue AM transmitters with varying degrees of adaptation. Most AM transmitters with digital (PDM or solid state) amplitude modulators can be adapted to transmit DRM30. Typically this will mean using a new low level driver which simultaneously offers a suitable signal to the high level amplitude modulator and a synchronised phase modulated input to the RF drive. For the foreseeable future (until broadcasters can contemplate turning their analogue transmissions off) all transmitters will need the capability to transmit analogue AM as well as digital DRM30.
It may not, however, be cost effective to modify older transmitters. A major factor in determining the suitability of transmitters using non-linear modulation techniques (PDM and PSM) will be the bandwidth of the existing audio modulator. In general this will need a bandwidth of at least 3 to 4 times the bandwidth of the transmitted signal. For example a transmitter intended to handle a 10 kHz wide DRM30 signal will need a modulator bandwidth of 30 to 40 kHz. This is because the DRM30 signal is constructed by simultaneously applying phase modulation to the carrier synthesiser and amplitude modulation to the (normal audio) analogue input with the two signals combined at the transmitter output to form the OFDM signal. Delay compensation is applied to the amplitude signal component to compensate for the different transition times of the two signals through the transmitter. The lower the modulator bandwidth the less accurate will be the delay compensation and hence the OFDM combination.
A DRM30 signal might also be transmitted using a ‘linear’ transmitter. The composite OFDM signal would be applied at the point where a low level analogue signal would normally be applied. A high level of linearity would be essential to avoid unwanted intermodulation products both inside and outside the allocated transmission channel. Some additional work may be needed to ensure that this required level of linearity is obtained.
In some cases it may prove possible to linearise a non-linear transmitter and then use it to transmit the composite signal as with the linear transmitter. However, this will generally give rise to a considerable reduction in the efficiency of the transmitter.
In the fullness of time – as the requirement for hybrid analogue / digital transmitters gives way to the need for digital only transmitters – it is likely that cost of a DRM30 transmitter offering the same output power as a converted AM transmitter will be lower. This is because while the voltage excursion at the transmitter output will be the same, the power handling capability will be less and therefore high cost components such as the mains transformer will not need to be as big and hence will be less expensive.
For DRM+, it is much less likely that an existing VHF Band II FM transmitter could be modified to work with a DRM+ signal. While perhaps a little easier to contemplate modifying an existing TV transmitter operating in VHF Band I, it is unlikely that this would be a commercially sound proposition. While it may be possible to modulate the phase of an FM transmitter, these devices are specifically designed to hold the output level constant. Any modification to allow the transmission of OFDM would probably be more expensive than buying a new linear transmitter. A linear transmitter suitable for DRM+ is likely to be much smaller and hence much cheaper than the higher powered transmitter needed for DRM30.
In any case, the transmitter needs to be accompanied by a DRM ContentServer (i.e. audio and data encoder and DRM multiplex generator), and a DRM Modulator (sometimes called a DRM Exciter).
Today, various manufacturers provide commercial transmission equipment for both DRM30 and DRM+.

5. What is the regulatory position regarding DRM – can it co-exist with existing analogue transmissions in the same bands?

DRM30 has been adopted by the ITU as a suitable system for digital sound broadcasting under Recommendation ITU-R BS.1514 "System for Digital Sound Broadcasting in the broadcasting bands below 30MHz". DRM+ is currently seeking adoption by the ITU into Recommendation ITU-R BS. 1114 "Systems for terrestrial digital sound broadcasting to vehicular, portable and fixed receivers in the frequency range 30-3 000 MHz". DRM30 transmissions are thus permitted by Rec. BS.1514 and DRM+ transmissions can be authorised by individual administrations on the basis that they will not cause interference to exiting licensed services. Both DRM30 and DRM+ are standardised at ETSI as ES 201 980 "Digital Radio Mondiale (DRM); System specification".
The basis of most regulation of the use of spectrum is the limitation of interference. The re-use of a particular channel is authorised on the assumption that the transmitter power and antenna directivity characteristics of one service do not cause undue interference to another service using the same channel within its intended service area; and, of course, vice versa. The relevant ITU-R recommendations define the acceptable levels of interference. The idea can be extended to interference caused by transmissions in adjacent channels if it is known how much energy from the transmission falls outside the specified channel bandwidth. Whilst this is likely to be much smaller than the in-band energy, it still has the potential to interfere with other transmissions, particularly if the service areas are geographically close. To be able to manage the situation and calculate the interference potential, the ITU-R Recommendations put limits on the amount of energy that is permitted outside the specified band for different modulation schemes.
In most of the frequency bands used for broadcasting it can usually be assumed that all of the broadcast signals within that band have the same technical characteristics. This simplifies the process of channel allocation because it can reasonably be assumed that the interference potential of any one service is mirrored by the other. Where different modulation schemes, such as DRM and analogue, are used in the same band, the differential interference effects of DRM into analogue and analogue into DRM must be calculated and taken into account in the planning process. As well as the planning parameters necessary to ensure that DRM30 signals do not interfere with each other, in the bands below 30MHz, ITU-R Recommendation BS.1615 includes the differential parameters needed to ensure compatibility between analogue AM services and digital DRM services. Equivalent planning parameters for DRM+ are currently being prepared for submission to the ITU seeking incorporation into the relevant ITU-R Recommendation.
Both DRM30 and DRM+ have been specifically designed to be compatible with the planning rasters in the relevant bands. DRM30 has modes which include all channel bandwidths used for AM broadcasting (e.g. 9 kHz for MF in Region 1, 10 kHz for HF globally, etc.). Similarly, DRM+ occupies 100 kHz such that two DRM+ signals will fit into a conventional 200 kHz FM channel. This means that it is relatively easy to introduce new DRM transmissions alongside analogue transmissions in the existing bands and similarly to replace existing analogue transmissions while staying within the interference limits specified by the ITU.
A DRM signal carrying the same programme content as an analogue signal (a so called "simulcast") may be placed in any available spectrum, it does not need to be co-located or in an adjacent channel, although these options are also possible. This is because DRM provides an Alternative Frequency Signalling feature. Broadcasters may provide information that keeps receivers constantly updated with the frequency information for alternatives to the currently tuned service and the receiver, by channel sounding, may determine which of these provides the best quality signal. The user therefore does not need to worry about retuning the radio as he moves around.
DRM also offers the option of single frequency networks (SFNs). This allows a multitude of transmitters to all broadcast on the same frequency which can make planning and coverage expansion a simple task.

6. Will it be possible to have stereo transmissions with the DRM system?

As a potential replacement for analogue FM, DRM+ has been conceived with stereo as a basic requirement. Also, with DRM30 there are transmission modes which will support a sufficiently high bit rate to allow stereo audio to be carried, for example in Asia with 18 kHz MW channels. However, in many other cases parametric stereo can be used, which provides a stereo experience in 9 or 10 kHz channels in the MW and LW bands.
In addition, the DRM system allows 5.1 or 7.1 surround sound based on the MPEG Surround standard. This is fully transparent to, and compatible with, mono or stereo DRM receivers, while surround sound capable DRM receivers can render an impressive 3D sound image. The required extra bit rate is typically in the range of only 4 to 10 kbps. Listening environments suitable for surround sound include high-end cars, home theatre installations, or mobile radios that support the MPEG Surround 'Binaural Rendering', which reproduces 5.1 surround sound on ordinary stereo headphones.

7. Why has the DRM system been developed, surely the internet will be the future of broadcasting?

While it is clear that the internet is indeed developing as an important new tool for broadcasters to use in disseminating their programmes, for the moment it lacks any credible method of delivering programming to a mobile audience. Ignoring connection charges, the need for the user to have a PC, typically with a cost many times that of a radio, and to provide a connection to the internet also means that, as a delivery method, it remains out of reach for the majority of the world's population. In time this may change, but the internet will for many years, if not forever, be a very inefficient method of delivering programmes to a mass audience. Broadcasters today have to strictly limit their listenership over the internet due to cost elements that scale almost linearly with the number of listeners. The great advantage of broadcasting using radio transmissions is the ease with which a huge number of people can be covered by a one-to-many delivery system. The internet retains its origins as a one-to-one delivery method - not an efficient broadcasting system when audiences in the millions need to be reached simultaneously.
For this reason it can be seen that radio broadcasting will live for many years and possibly forever as an efficient way of connecting content makers with their audiences. It follows that there is considerable value in improving the way in which valuable broadcast spectrum is used. The development of a digital transmission standard which can provide a significant quality improvement whilst using the same amount of spectrum is a valuable investment for all those involved in broadcasting, not least the listener.

8. Will the same digital radio system be used everywhere in the world?

Although highly desirable, it is unlikely that a single digital radio system will be used everywhere. DRM has been designed to be globally deployed since it fits with all the existing analogue radio bands. DRM is the only digital radio system that is sanctioned for use in the LF and HF broadcasting bands by the ITU. The ITU recommendations for digital radio broadcasting describe various other digital radio systems in addition to DRM - namely Digital Audio Broadcasting (DAB), IBOC (HD Radio) and ISDB-T.
The DAB system provides a spectrum-efficient and cost-effective system where a multitude of broadcasters are providing content over an identical coverage area. It is currently used in various countries in Europe and Asia in VHF Band III. Like DRM, DAB is an open standard, and both systems share key elements like service signalling, audio coders and data applications, and support their joint deployment in a region through service cross-referencing (allowing a receiver to find the same service on the other broadcast system).
The HD Radio system, developed by the US company iBiquity, may be used in the MF Band and VHF Band II. It provides the ability to blend seamlessly from digital to analogue and back as coverage varies, and allows additional audio streams. The system has been tailored to exploit the band planning arrangements in the USA and is currently used by many broadcasters in North America.
ISDB-T is used in Japan and allows radio and TV to share a common transmission standard. Radio receivers decode a part of the signal, TV receivers decode it all.
There are some synergies between these systems – particularly DAB and DRM – and it is perfectly feasible to build receivers that work with some or all of them in such a way that the operation is seamless to the listener.

9. Does DRM have a "simulcast" mode that allows simultaneous transmission of analogue and digital signals in the same channel and will existing analogue receivers work with it?

A number of simulcast modes are detailed in the DRM system specification. In some of these the analogue signal is transmitted as a single sideband signal with a carrier, in others as a full DSB signal. The option that might be used will depend on the bandwidth which is available either side of the channel. If these simulcast modes are used then existing analogue receivers will be capable of receiving the analogue signal.
DRM30 supports both single channel simulcast and double channel simulcast. Single channel simulcast describes a signal which carries both an analogue (SSB) and a digital signal component (half channel, 4.5/5 kHz) within one 9 or 10 kHz broadcast channel. Although this setup allows both a compatible analogue and digital signal in a single channel, unless the channel is very flat (e.g. an LF channel) tilt will degrade the AM quality and since there is only a half channel for the DRM, the audio quality of the digital signal will be poor. Double channel simulcast, however, is a very attractive option in regions where AM broadcasters have either 18 or 20 kHz wide allocations; if approved by the relevant regulatory body and agreed with the users of neighbouring frequency assignments, a full DSB analogue and full channel DRM signal may be transported side by side (either 9 + 9 kHz or 10 + 10 kHz).
DRM+ allows the transmission of a full DRM+ signal (100 kHz bandwidth) next to a 200 kHz analogue FM signal. In regions with 400 kHz FM channelisation, this mode allows for a simulcast transmission while staying within one FM channel. The DRM system specification describes the minimum signal spacing and power level differences for this operational mode.
Even in the simulcast modes the digital and analogue components are actually separate signals. The digital signal is a multi-carrier signal without a central carrier. The analogue signal remains completely unchanged with its associated carrier and is demodulated by an analogue receiver in the usual way. To the analogue receiver, the digital signal will appear purely as a non-coherent noise-like signal. Provided the level of the digital signal is set correctly, the noise level induced in the analogue receiver will be negligible.
From a digital listener standpoint, the location of the analogue and digital signals within the frequency bands is completely irrelevant, since services are selected by station names and not frequencies and the receiver will find and follow the best reception method currently available for each service. From an analogue listener standpoint, the location of the analogue signal should remain in its existing place so that they are not affected. Analogue listeners will only be concerned by digital signals if they cause interference, and proper planning will avoid this.

10. What effect will the transmission antenna have on the DRM signal?

The antennas used for FM broadcasting in VHF Band II are typically wide band structures capable of handling a number of FM signals at different frequencies. Such antennas should therefore be perfectly suitable for the transmission of DRM+, since a DRM+ signal is narrower in bandwidth (100 kHz) than an FM signal (c.200 kHz). Similarly, an HF broadcast antenna is usually a broadband structure and, since DRM30 signals at HF are no wider in bandwidth than analogue HF signals there should be no issues with antennas.
At lower frequencies the situation is a little different as antennas for MF and particularly LF broadcasting tend to be much narrower in bandwidth. The effect of reduced antenna bandwidth on an analogue AM signal is to cause a loss of the higher audio frequencies due to a roll-off in the level of energy transmitted towards the outer edges of the upper and lower sidebands. Although this effect does reduce the quality of the received signal it is not disastrous and can often be compensated for by the use of audio frequency compensation in the transmitter chain. With a DRM30 signal a significant fall off in the response of the antenna at the outer edges of the transmitted signal will lead to the outer carriers being transmitted at a reduced level compared to those nearer the channel centre. This will mean that the signal to noise ratio of the outer carriers will be reduced at the receiver when compared to the inner carriers. If the fall off is only small (a few dBs only) this may not be significant, but if it is large (10 dB or more at +/- 4.5 kHz) it will impact on the received signal reliability and the antenna will need some compensation. Experience suggests that the problem is often most acute in directional or multi-element MW antennas and in LW antennas. Care will be needed if remedial work is carried out, as a simple audio frequency compensation network applied to the DRM30 signal may well not provide the same improvement that can be obtained with an analogue signal. In the case of antennas used for transmitting on more than one frequency, attention will be need to be given to the phasing, matching and coupling networks, since these can often introduce undesirable effects in the frequency and phase response of the transmitted signal which can adversely impact on the spectrum of the transmitted DRM30 signal.

11. What is the spectrum occupancy of a single programme using DRM?

With DRM30 the spectrum occupancy of a single programme is between 4.5 kHz and 20 kHz depending on the mode. Besides the single channel bandwidth options of 9 and 10 kHz spectrum occupancy, DRM30 also supports half (4.5/5 kHz) and double (18/20 kHz) channel options. Clearly the mode has to be chosen to suit the amount of spectrum available. Also, the audio quality of the transmitted signal will increase as the bandwidth increases. Particularly using the higher bandwidth modes it is possible to fit two or more audio programmes into the DRM30 signal.
The bandwidth of the DRM+ signal is fixed at 100 kHz. Within this is it possible to transmit up to 4 stereo audio programmes. Clearly there will be a trade off between audio quality and the number of programmes multiplexed together. However in its most 'frugal' mode the 'effective bandwidth' occupied by a single audio programme is 25 kHz.
In general there is a high degree of correlation between the left and right hand channels of stereo audio. In practice this can be used to reduce the bit rate where true, independent channel, stereo is not essential.

12. What are the licence fees / royalties required for DRM?

DRM is an open standard: all information relating to the technology is published in a series of standards administered by ETSI.
• The DRM Consortium does not own any DRM patents and is completely divorced from the entire technology-licensing process.
• DRM Technology licensing is handled by VIA Technology (www.vialicensing.com), on behalf of a group of licensor companies.
• There is no running-royalty or other charge to broadcasters or listeners for use of the system.
• Royalties relating to DRM equipment (transmitters, receivers etc) are paid by manufacturers to VIA Technology and thence to the relevant patentees.
• The DRM Consortium does own the DRM trade-mark, which is administered by DRM.