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Pilot Project to Test Digital Radio Transmission for Local Area with DRM (Digital Radio Mondiale) in Hannover

 

Digital Radio Mondiale (DRM)

 A new international standard on the digitization of the AM radio scope (Long wave, Medium wave & Shortwave) was introduced by the DRM-Consortium in the year 2004. The DRM consortium now consists of nearly 100 members from all continents, including 31 from Germany. Members are broadcasters, receiver and transmitter industry, network operators, research institutions, associations and regulatory bodies/committees.

DRM replaces the normally utilized analog AM broadcasts, improving audio quality for long, medium and short wavelength broadcasts, and audio quality is comparable to the nowadays FM transmissions.

Based on the fact that DRM can be used up to frequencies of 174MHz, it is possible to digitize Band II (FM Band) with this system (DRM+).

DRM and DRM + are the two versions of the DRM system family. They differ in the usable frequency range for the AM range DRM and DRM + for the FM range. DRM + is therefore not seen as a successor but as an extension of the DRM standard.

Up to four parallel Services can be transferred over a DRM/DRM+ multiplex. These services could include audio transmissions in different audio qualities, data transferring or other applications like pictures, etc.

Due to its structure associated with the relatively narrow bandwidth DRM can be used both as Single-Frequency Network (SFN) for a national coverage and also in Multi-Frequency Network (MFN) for the local area.

DRM in the AM range in the local area

 Local transmissions at medium wave frequencies are not feasible in Germany due to spectrum scarcity and the relatively large antennas needed. However, a very lightly used radio frequency range, the 11m-band (25.67 to 26.1 MHz) in the shortwave range with 43 channels is available. 

 

Phase 1 (August 1, 2005 to July 31, 2008)

Pilot participants: 

IKT, Leibniz University Hanover (technical director)   

Niedersächsische Landesmedienanstalt 

Starwaves   

In the model, the possibilities of using digital radio transmission technologies for local area have been studied. The usability of the 11m band for the dissemination of local radio has been investigated. Overshooting of radio stations or other radio services in other countries could disrupt the local distribution in the 11m band, however. These disorders are dependent on the nature of the ionosphere, including the time of day, time of year, as well as the solar activity and solar cycle. Other disorders might be experienced due to electrical equipment, ignition systems, trams, power line communication systems (PLC), return paths in cable networks, industrial plants at ISM frequencies, etc. It was investigated whether automatic frequency hopping could be used and the transmission could always be set up on an undisturbed frequency.  For this purpose, a radio program was transmitted with a number of different available frequencies. Interference in the transmission received from the PC-based DRM receivers in the experimental area, reported directly via the Internet to the broadcaster. A frequency change was applied in case of failure. Statistical analysis should show the impact of local or distant interferers to received signals and the strength of the disturbances. Field strength measurements on the ground should verify theoretical calculations and the results of the mobile measurements should show the transmission parameters to be set.

The results of the field test digital11 are available in the download area.

Phase 2 (since 1 August 2008)

Pilot participants: 

IKT, Leibniz University Hanover (technical director)   

Niedersächsische Landesmedienanstalt 

The DRM Consortium decided in Paris in 2005 to increase the standard DRM from 30 MHz to 120 MHz (174 MHz today). This leads to the possibility that DRM Band I (47 MHz - 68 MHz) and Band II (87.5 to 108 MHz, 65.8 to 74 MHz and 76 to 90 MHz) and higher frequency ranges can be digitized. DRM + can be scheduled in the FM band with the bandwidth of 96 kHz and can be transmit up to four applications, audio, video or data in one multiplex . For example, two high-quality stereo programs, each with 64 kbit/s kbit and two additional programs with lower data rates or data services with 24/s,  a total of up to 186 kbit/s, using the  modern coding procedure MPEG-4 HE AAC v2. 

Theoretical studies on DRM + are to be done and besides the transmissions in the 11-m band, comparative transmissions in band II are to be done. In addition, a Delay Diversity Transmitter operation will be tested under real conditions, as well as investigations in a Combined Mode (DRM + close alongside an FM signal).