Digital Radio Mondiale

Digital Radio Mondiale (DRM) is a narrow-band digital radio system for the dissemination of global, national, inter-regional and local / regional radio channels and data services and video formats. The DRM standard which originally included only the digital distribution of broadcasting services in the AM range, ie long, medium and short wave (called ' DRM30 ' ) with the four transmission modes AD. To use the system in the VHF areas of the DRM standard " DRM " was a mode E, called extended. So DRM can be used in the VHF range and together with DAB / DAB in VHF band III.

DRM is an open ETSI standard. He describes the audio encoding that v2 ( or one of the two speech codecs HVXC or CELP ) by means of MPEG -4 HE - AAC, the content server and the multiplexing of up to four offers ( audio, video and / or data services ), the interfaces and protocols and the channel coding and modulation by OFDM / COFDM with the different transmission modes AE.

• 4.1 Requirements and technical parameters

Formation

The DRM project was lifted in September 1996 at an informal meeting of some major international broadcasters in Paris from the baptism. (Now Transradio ) Represented German Telekom, German wave, Radio France Internationale, Telefunken, Thomcast (now THOMSON BROADCAST GmbH ) and Voice of America.

The official founding of the DRM Consortium took place on 5 March 1998 in Guangzhou, People's Republic of China.

System properties of DRM

Multiplex: In a DRM - channel up to four programs or data services can be sent simultaneously. Thus, the possible bit rate of each program is reduced. The radio uses Germany as a data stream, the latest news or internal information (" About us " ) radiates this but with very reduced bit rate and sound quality.

Data services: The broadcasting of texts and data is possible. The text-based news service News Service Jour Aline developed by the Fraunhofer Institute for Integrated Circuits and other companies for DRM and DAB enables a menu-based themes preparation, so that, for example, the latest news, information of the channel or program or regional traffic information can be accessed selectively. The service is optimized to be decoded and used on simple radio devices.

Video-/Bildübertragung: The Fraunhofer Institute for Integrated Circuits developed a video extension for DRM " Diveemo ," such as education and information content can be transferred to the. Diveemo is optimized for very low data rates to transmit video content easily and cost-effectively. The standardization in ETSI is currently running (as of March 2012).

Automatic Frequency Switching ( AFS): alternative frequencies can also be sent as RDS, but with DRM even furnished area, time and day of the week can be specified in more detail.

Electronic Program Guide ( EPG): Similar to DVB can also be offered via a DRM EPG, but which is kept very simple because of the low bandwidth.

Text messages: Similar to the radio text for RDS can also be transmitted information about the current program, the transmission site used, program announcements, news, etc.. Also underlining and bold are possible.

Time: About DRM the current time can be transmitted.

Program type ( PTY): Similar to RDS program type identifiers may be broadcast.

Simulcast: Technically, it is possible to simultaneously AM and DRM broadcast on one frequency. The process is referred to as single channel simulcast method ( SCS). Handset with AT devices can continue to use these therefore. DRM listeners enjoy a distortion-free signal. However, the DRM - sound is dull in this case, since only low data rates are used. Unfortunately it has to be significantly faster than the digital DRM component of the signal to keep the background noise in analog reception bearable, since in most commercial receivers, the IF bandwidth is not narrow enough in the SCS mode, the AM signal. This of course reduces the DRM coverage area quite significantly compared to a purely digital transmission. This solution is therefore a compromise and is currently hardly used after some tests.

Single-frequency operation: To increase the reliability of the received signal allows the DRM system, multiple transmitters at different locations on the same frequency ( single frequency network - SFN) to operate.

DRM to 30 MHz ( DRM30, A- D mode)

Propagation conditions and routes

Long wave

The long wave spreads during the day as ground wave and adapts to some extent to the curvature of the earth at. This is, depending on the radiated power, range possible by 1000 km. Radiated room at night Shares are reflected at the E- layer and can be used in long distances damped reach Earth. In Europe, more than 15 long-wave channels are possible, so that not every state can run your own long-wave transmitter interference.

Medium wave

The center shaft also common during the day as a ground wave, however, the range will be less through the bottom wave attenuation than in the long-wave and can be up to about 500 km. In the evening and night hours, the space wave components of the ionospheric E- layer are reflected. This additional space wave ranges of more than 1000 km may occur. However, this reflection is not always uniform: The signal of the space wave is swallowed by the ionosphere at larger distances from time to time, sometimes beyond recognition. This effect is known as fading or shrinkage. To avoid co-channel interference, it is therefore necessary, in the evening and at night the particular abnormal situation adjust the transmitter powers, so to reduce it. In the medium wave broadcast band are 121 channels available in Europe. Depending on the further assignment of the respective frequency must be reduced at night due to the space wave propagation, the power or shut down completely. Otherwise, the respective frequency can be used to supply the entire European region.

Shortwave

In the short-wave wave soil hardly plays a role in spreading. The transfer to the target area is primarily via ground waves. Depending on the season, time of day and number of sunspots - which significantly affects the reflectivity of the ionosphere - you can use certain radio bands of the shortwave for different target ranges. Here, a short wave broadcast quite make several jumps ( hops) between the ionosphere and the earth's surface and thus bridge several 1000 km, to be heard in the target area. This produces but next to the mentioned in the medium wave fading, which is less pronounced on shortwave, especially so-called selective fading, which on the frequency interferes with the transmission signal dependent places. On the short wave are dependent on the distance and the variables mentioned above several hundred transmission channels.

To realize local supplies via shortwave, the 11- m band ( 25.67 MHz to 26.1 MHz ) can be used. This frequency band is relatively free in Central Europe and has 43 channels. Worldwide tests and studies have shown that even with low power (up to several 100 watts ) regional supplies and supplies of cities portable indoor, outdoor and mobile are possible. In times of high sunspot number, however, can occur even at relatively low transmitting power overreach that can cause disturbances in distant areas. The use of DRM in the 11- meter band, therefore, focuses not on the advertising- supported broadcasting, but rather on the non-commercial radio and college radio.

Bandwidth requirements

A DRM channel used on long and medium wave

• 9 kHz in ITU Regions 1 and 3
• 10 kHz in ITU Region 2

On short-wave 10 kHz bandwidth are provided worldwide.

In addition, transfers are not feasible with

• 4.5 or 5 kHz bandwidth ( especially for narrow-band transmissions )
• 18 or 20 kHz bandwidth ( if a high audio quality is required or more programs to be broadcast in a data stream with high quality at the same time )

In amateur radio, a modified DRM is used with 2.5 kHz bandwidth in order to comply with the IARU band plans. It is used because of the very low bandwidth audio codec Speex or linear predictive coding.

OFDM transmission modes

For four transfer DRM30 (AD) are specified that differ in their OFDM system parameters, and the resulting data transfer rates:

(*) Mode is not provided on long and medium wave (only short wave )

Mode A is primarily intended for local programs on the long and medium wave, in which the transfer outweighs the ground wave and accordingly there is virtually no fading. Recently, however, discovering more and more providers that also, under certain conditions shortwave transmissions in Mode A (when using 16QAM ) are possible in order to improve the data rate and thus the sound quality.

Mode B is mainly in short-wave transmissions with only one reflection at the ionosphere (so-called "single hop" ) popular. These are channels that are to be received, for example, only within Europe. Some long and medium wave transmitter at night also more likely to prefer Mode B, since at night even in these bands, the space wave is involved in the wave propagation.

Mode C can be used for shortwave broadcasts across continents. Since these distances, the waves are reflected several times between the ionosphere and the earth back and forth (so-called " multi- hop" ), it is here reinforced the superposition of waves with different maturities and thus signal gains and signal loss. In general, nevertheless, one also uses the overseas supply mode B, as it provides a higher data rate.

Mode D is the störungsunempfindlichste transmission mode and is mainly used for NVIS communications (Near Vertical Incidence Skywave ) is used. This transmission mode is not likely to spread in Europe, well, it will be used in the tropical regions to the corresponding frequency bands. Here, because the waves are radiated nearly perpendicular to the sky, it comes in addition to the fading effects already mentioned, in addition to Doppler shifts, since the height of the reflecting layers of the atmosphere fluctuates constantly above the ground.

In practice, most providers use in the AM bands mode A or B, only a few ( for example, the German wave) use under unfavorable conditions, the mode D; so also reduces the audio quality. Radiations in Mode C are very rare.

Mode B finds lately increasingly common in amateur radio use.

Error protection classes

Within the four OFDM modes, there are four different error protection classes which have different levels of transmission rates. The higher the protection, the lower the effective data rate. Due to these errors protective measures ( redundancy) AM- typical effects like fading, selective fading, atmospheric disturbances and disturbances can be compensated by adjacent stations. Due to the limited data rate of critical propagation conditions may compromise between a higher error protection for a good reception quality and the resulting decrease in net bit rate for audio transmission must be found in the event.

The table shows typical bit rates in the respective modes and classes of protection in the use of EEP (equal error protection) in kbit / s

For the majority of the DRM broadcasts Mode A or B is used today in the protection class 1, wherein Mode B is most commonly found on shortwave.

By the use of AAC in combination with the so-called " Spectral Band Replication " (abbreviated SBR) reach an audio bandwidth of 15 kHz ( from 22 kbit / s) with a bandwidth of only 9 or 10 kHz in the radio frequency spectrum. The spectral components between 6 kHz and 15 kHz are not perceived with the transparency or brilliance of a CD or FM transmission.

The modes C and D are currently only the demonstration of the ratio of insensitivity to fading and the achievable bit rate.

The audio quality of the modes C and D is relatively modest when using AAC and only slightly better than the conventional AM broadcasts. If moreover a high protection class used, they may even be perceived as worse than the analog transmissions, because the type of interference is unusual. Although this point may at first seem unattractive the last two modes, still applies ( if there is enough noise and signal to noise ratio ), as with all digital broadcasts in terms of sound ( picture) Quality: transmitter signal = received signal, the sound is so clear of noise, crackling and whistling. In addition, along with a standardized DRM voice encoder ( HVXC and CELP ) a good to very good speech quality can be achieved, so that these modes can be attractive at least for information programs due to their robustness again.

Audio quality

The DRM system was originally designed for the boundary conditions of the distribution on short, medium and long wave ( DRM30 ). Despite the narrow RF bandwidth of 9 kHz or 10 DRM30 offers better audio quality than analog AM broadcasting, which is also free of disturbance.

The audio quality is the use of SBR (HE -AAC ) with the data rates of 16-26 kbit / s. DRM30 over much better than AM stations

Radio programs

Currently radiate some stations worldwide every day broadcasts in DRM from.

The German wave and the BBC, both founding members of the DRM Consortium, have set their common DRM Service for Europe in the fall of 2010. The BCE ( Broadcasting Center Europe ), technically responsible for RTL radio from Luxembourg on the medium wave 1440 kHz and shortwave 6095 kHz, the emanations reduced in DRM mode ( in February 2011 on the short- wave only in the order of 1 h / day). From Berlin- Britz Germany, the radio sends its digital program DRadio knowledge on medium wave 855 kHz around the clock for the Berlin-Brandenburg region. Parallel to this program, a non-stop news channel and news stories are available in text form on the frequency.

Oldie Star Radio was the first German private stations, which broadcast its program in DRM mode. As of 2005, the program was disseminated in 1485 kHz in Berlin on medium wave. Also stations from Eastern Europe, such as the Foreign Service of the Polish Radio, Radio Romania International and the Voice of Russia broadcast their programs from the DRM system, but usually only for a few hours a day. Since 26 May 2008, including Radio Bulgaria broadcasts its domestic program in Bulgarian and, since 2009, various foreign language programs across Europe in DRM from, including the co-production with other transmitters " Euranet ".

End of March 2009, the regular DRM transmission operation in Russia and at All India Radio was recorded on shortwave.

Overall, however, DRM has so far - probably mainly due to the small number of recipients - still not gain significant market importance.

DRM in VHF bands from 30 MHz ( DRM , Fashion E)

In 2009 came the ETSI standard of the DRM system added a E ( DRM ) mode. In order for a transmission in the VHF bands (up to 300 MHz) is feasible. After successful studies of the FH Kaiserslautern and the University of Hannover from the years 2009/2010, earnings before that DRM in VHF band III ( 174-230 MHz) is technically feasible. After recording of DRM in the ITU end of 2011 as "System G" for transmission in the frequency range 30-300 MHz and the ETSI standard for DRM is now adapted to it. This allows the DRM system not only in the FM radio sector ( 87.5-108 MHz ) are used, it is also positioned as a future addition to the digital radio standard DAB / DAB in VHF band III ( 174-230 MHz ), especially for the proliferation of digital radio programs in the regional or local distribution areas and for programs that have a very high regional report factor.

For frequency- technical realization there is enough free capacity for DRM in VHF band III without affecting the planned coverage for DAB . A DAB block ( with 1.5 MHz wide) could in principle be divided into around 15 DRM blocks. That is, in a DAB cover around 15-30 DRM - radio programs and additional data services for the region can be disseminated. The use of DRM in VHF band III had over the DRM planning in the FM frequency band has the advantage that no complex usage and transition scenarios would have to be digital and analog developed for the FM band II and gem in the VHF band III. RRC -06 and other digital systems could be coordinated as a DAB, provided they meet the Störkriterien of Eureka 147. The band III is for such use are available, and which would incidentally also contribute to "secure " the band III over other broadcasting foreign usages.

Requirements and technical parameters

• Implementation of data rates that allow the reception of at least one radio program in CD audio quality;
• Supply range and safety at least as the current VHF-FM supply with the possibility of mobile reception at high speeds and portable reception in the house;
• Transfer of existing structures in the present FM radio (local, regional, statewide and national broadcasting formats );
• Useful bandwidth of 100 kHz to maintain the current FM planning grid;
• Avoid disruption of existing VHF-FM supply to implement a gradual migration of broadcasters.

• Transmission scheme: OFDM with co-channel capability;
• Number of subcarriers: 213;
• Carrier spacing: 444.44 Hz;
• Modulation of the subcarriers: 4 -QAM or 16 -QAM;
• Bandwidth: 96 kHz;
• Data rate: 375-186 kbit / s;
• MPEG-4 AAC audio encoding.

DRM receiver

For DRM30 (as of May 2012) are currently few receivers available on the market, mostly through online stores on the internet. This also applies to the DR111 from Chengdu NewStar Electronics, which is has met the DRM Consortium minimum criteria for receivers and distributed worldwide.

The Fraunhofer Institute for Integrated Circuits (IIS ) currently offers a prototyping board based on FPGA for the complete DRM signal processing.

Another way of DRM reception offer software-defined radio receiver ( SDRs ). The control of such receiver and demodulation (decoding ) of the DRM signal is happening with a microcomputer or a PC.

History and future of DRM

With the introduction of the new standards in June 2003 at the "World Radio Conference " in Geneva, the program hours International stations on the AM bands declined. Many broadcasters moved their shows on satellite channels or focus on distributing through FM relay stations and web radio. Therefore, many observers Digital Radio Mondiale saw when it was introduced as " the future of shortwave ", with the old technology would be transferred to the digital environment. As an advantage, the continued use of existing broadcast equipment was seen.

2008 were broadcast over 700 hours of broadcasting DRM. Two large main initiators of the technology, the German wave and the BBC, withdrew from the development in 2012. Weaknesses are still (as of 2012) and the small number of DRM -capable receivers and the small market significance of this technique. In addition, the DRM broadcasts are in various data formats. Overall, the DRM technology could not halt the continuing degradation of AM broadcasting capacity. Many DRM broadcasts can be set because the operators take or degrade the corresponding transmission equipment out of service. In Germany, both the WDR and the BR sent in DRM on medium and short wave. However, both stations gave up their AM transmitters and thus the DRM broadcasts.