Radio analog technology was used for broadcasting for decades. After the advent of digital electronics, a new type of radio technology emerged – the digital terrestrial broadcasting. As opposed to the linear transmission of sound in analog, digital radio uses compressed digital signals for radio terrestrial broadcasts. As analog signals suffer from quality loss due to signal interference and obstructions, the digital radio, on the other hand, offers an excellent audio quality.
Among the several digital radio technologies, one of the key digital radio standards is called Digital Radio Mondiale (DRM), where ‘mondiale’ is the French word for “worldwide”. DRM is the latest global, open (non-proprietary) digital radio standard that allows for broadcasts in all AM/FM frequencies, but in digital format.
The DRM Consortium has lately been using the terms DRM for AM, instead of DRM30, and DRM for FM bands, instead of DRM+, to stress that DRM is one unitary standard (not two), as it might be perceived sometimes, enjoying the same features and benefits, irrespective of the band in which it is used. DRM is more spectrally efficient than analog AM and FM, allowing more stations, at higher sound quality, into the existing analog bandwidth, with the advantage that up to 3 programs and one data channel can be broadcast instead of one single analog AM or FM program.
The DRM radio broadcast is done using advanced digital technology. On the transmitter side, first the audio and data are processed using an encoder/multiplexer. Using Multiplex Distribution Interface (MDI)/ Distribution & Communication Protocol (DCP) data is modulated to COFDM signals and broadcasted using a dedicated DRM AM/FM transmitter. On the receiver side the unit converts the radio signals back to MDI/DCP data using the demodulator. The data is decoded back to audio and data using the demultiplexer which can be controlled using the Receiver Status & Control Interface (RSCI).
Some Historical Background
Radio broadcasters including Radio France International, TéléDiffusion de France, BBC World Service, Deutsche Welle, Voice of America, Telefunken (now Transradio) and Thomcast (now Ampegon) took part in the formation of the DRM not-for-profit Consortium. Afterwards, many meetings were held around the world till 1999 that resulted in the launch of the International DRM Consortium in Guangzhou, China. The DRM Consortium then became a sector member of the ITU (International Telecommunications Union).
In April 2001 the ITU ratified DRM as the digital standard for the broadcasting bands below 30 MHz. In 2003 the world’s first DRM broadcaster Deutsche Welle started the DRM shortwave broadcast in Geneva during an ITU meeting there. In March 2005 the DRM consortium voted to begin the process of extending the same system to the VHF bands up to 108 MHz (and later beyond that), which covers the FM bands. Finally on 31 August 2009, DRM was extended to the FM bands (Mode E). And the technical specification was published by the European Telecommunications Standards Institute (ETSI). According to the specifications, the DRM Mode E or DRM for FM can be used for radio broadcast above 30 MHz up to 230 MHz (VHF in bands I, II and III). Moreover, DRM Mode E or DRM for FM offers the flexibility to upgrade existing analog FM transmitters to DRM and allows also for simulcast analog/DRM. The DRM transmitters can consume 50%-90% less energy than the analog transmitters and that is why DRM is green and very energy efficient.
DRM uses Coded Orthogonal Frequency Division Multiplex (COFDM) technology for radio transmission, which resolves the fading problem (common in analog radio) and with the help of cheap but efficient computer processing power – DRM uses modern audio compression techniques that enable more efficient use of available bandwidth, at the expense of processing resources.
DRM broadcasts use the latest xHE-AAC audio coding format. As DRM provides a better radio transmission and superior audio quality, many international broadcasters have switched from analog to DRM; among them the BBC World Service, All India Radio (AIR), Voice of Nigeria, Radio Romania International, China National Radio and others (for details go to: schedule.drm.org).
DRM means very good audio, but it also provides many useful multimedia applications such as DRM Text Messages, Journaline advanced text with listener interactivity and geo-referenced information, slideshows, traffic updates via TPEG/TMC, service logos via SPI, etc.
DRM Works In All Frequency Bands
The following diagram illustrates clearly the use of the DRM standard in all frequencie, both below and above 30 MHz.
DRM Demonstrated in All Frequency Bands
DRM in AM has been extensively tested and is used for current broadcasts.
Indian stakeholders for instance have carried out a thorough DRM in FM demonstration in both Delhi and Jaipur last year.
During the trial it was confirmed that adding DRM transmissions to the FM band is fully compatible and does not interfere with on-going analogue FM services. Also, DRM as a pure digital radio standard proved its ability to efficiently broadcast multiple DRM signals side-by-side from a single transmitter (multi-DRM transmitter configuration, not to be mistaken with the multiplex solution offered by DAB+), and for operating in flexible configurations alongside an analogue FM signal from the same transmitter (simulcast transmitter configuration).
DRM can also deliver additional Journaline advanced text service in multiple Indian languages, to be ready for delivering Emergency Warning Functionality – EWF in case of disasters (with CAP interface), and to efficiently enable traffic, travel, and online teaching services over free to air broadcast, without requiring Internet connectivity.
Reception of DRM services in the FM band was demonstrated on various consumer receivers of various types, on car receivers, and on mobile phones. It was proven that existing receiver models, already supporting DRM in the AM bands, as adopted by India, can support DRM in all bands by a simple firmware upgrade without hardware modifications.
The DRM radio broadcasts are done using advanced digital technology. On the transmitter side, first the audio and data are processed using encoder/multiplexer and using Multiplex Distribution Interface (MDI)/ Distribution & Communication Protocol (DCP) data is modulated to COFDM signals and broadcasted using a DRM AM/FM transmitter. On the receiver side the receiver converts the radio signals back to MDI/DCP data using the demodulator. The data is decoded back to audio and data using the demultiplexer which can be controlled using the Receiver Status & Control Interface (RSCI).
When DRM was originally designed, it was clear that the most robust modes offered insufficient capacity for the state-of-the-art audio coding format MPEG-4 HE-AAC (High Efficiency Advanced Audio Coding).
However, with the development of the latest MPEG-4 xHE-AAC, which is an implementation of MPEG Unified Speech and Audio Coding, the DRM standard was updated and the two speech-only coding formats, CELP and HVXC, were replaced.
Now MPEG-4 xHE-AAC has become the standard codec for DRM radio and the xHE-AAC combines two MPEG technologies, High Efficiency AAC v2, and Unified Speech and Audio Coding (USAC). It is designed to support the delivery of mixed speech and general audio content including music on mobile devices, radio broadcasts, and wired streaming services. xHE-AAC provides exceptional audio quality using even very low bit rates delivering a listening experience suitable for mobile devices and can scale-up to offer audiophile-quality reproduction. The reduced bit rate helps broadcasters and mobile streaming audio providers distribute their content more efficiently. Consumers can enjoy high quality audio reproduction at lower bit rates, which reduces their mobile data consumption and costs.
It is anticipated that, in future, most broadcasters will adopt xHE-AAC, widely used in cellphones/mobiles.
Since DRM radio broadcast uses COFDM technology, the broadcasted signals are less prone to RF interferences and quality loss. This makes DRM radio one of the best technologies for radio broadcast. The use of digital radio technology with OFDM and many latest audio codecs like MPEG-4 xHE-AAC, makes DRM the most advanced and superior radio today
A DRM radio broadcast can only be received by using a DRM receiver (All DRM receivers are also capable of receiving analog radio, although analog receivers cannot be converted to digital). Such a digital receiver comes with a user interface consisting of station selection buttons and a display screen. The receiver demodulates the COFDM signals of a DRM broadcast and decodes the audio and data that comes with the modulated radio signals. The audio is converted to sound and played through the built-in speaker, while any data in the form of text or image is displayed on the LCD display of the receiver. More and more manufacturers are in the process of planning and producing DRM receivers. For more information on DRM receivers, visit https://www.drm.org/products-solutions-and-technologies/
Benefits of the DRM Standard
DRM is a digital radio that uses the latest technology for radio broadcasting with high sound quality audio and with data information (text/image), which can be received using a DRM receiver. The benefits of DRM fall under three headings – Universal Access (connecting the citizens of an entire country), great flexibility and green (energy efficient) credentials.
- Universal Access (connecting the whole country) – DRM radio can broadcast to the whole country using AM bands. As the LW/MW/SW band radio signals can travel thousands of miles from one country to another, DRM for AM broadcasts cannot only give access to news and information to the listeners of one country, but also to the listeners of many other countries on different continents. Moreover, unlike any AM analog radio, a DRM receiver can also deliver data including text and images, news, general information, emergency warnings, distance education to the listeners. The emergency alerts feature (EWF) makes DRM not only an information provider, but also a life saver during any crisis, like natural disaster and pandemic outbreaks.
- Flexibility – DRM, being an open standard has no secret algorithms like those of the HD IBOC system, therefore is very flexible. This flexibility makes DRM for AM and DRM for FM especially easy to implement. As DRM can be used in the FM band, it is possible to upgrade the FM transmitters to DRM without affecting the existing analog FM broadcasts. A DRM broadcast can be carried out alongside the analog FM broadcast.
- Green (energy efficient) – DRM is a green standard, as it consumes less power. DRM for AM transmitters can consume between 50-80% less power when compared to other analog transmitters. For DRM in FM the energy savings can go as high as 90%. Such low power consumption of DRM radio makes it one of the best energy efficient radio technologies in the world.
With the advent of newer technologies and cheaper digital audio electronic components like digital signal processor (DSP), digital-to-analog converter (DAC), system on a chip (SoC), etc., the manufacturing of digital radio equipment has become possible and much more cost-effective, as the over 4.5 million Indian cars with line-fit DRM receivers attest. With the help of such digital electronics and state-of-the-art technology, with the development of software defined radios (SDR) DRM radio can let the listeners experience high quality digital audio along with information in the form of text and images.
DRM radio is on the rise. With serious orders to global manufacturers, more and more receivers, at lower costs will be made available to listeners who will be able to enjoy DRM’s useful features and benefits, thus providing the ultimate digital radio experience.
Source: Digital Radio Mondiale
Author: Debojit Acharjee
The author is a software engineer and likes to geek about various software technologies. Apart from that, he also likes writing articles related to science and technology. He has written many articles related to software technology and computer science, and has knowledge about various software technologies like Robot Process Automation (RPA), Artificial Intelligence (AI) & Machine Learning (ML), blockchain, DevOps, database management, and also knows many programming languages. Besides that, he also knows about various multimedia software used for audio/video editing and production purposes. His passion for computers makes him work hard, and he believes that success comes in life only through hard work and good skills.
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