Digital Radio Mondiale (DRM) is a group of digital audio broadcasting technologies that were designed to work over shortwave bands used for AM broadcasting. DRM is the only open standard digital system for different bands below 30 MHz that uses existing frequencies and bandwidth across the globe. However, the DRM consortium plans to extend the system to bands up to 120 MHz.
DRM provides near-FM sound quality and data content for display on the DRM receiver with an ease that comes from digital transmissions. It can be used for audio content and can integrate text and data which can be displayed on DRM receivers for a better listening experience. The technology can fit more channels into a defined bandwidth as compared to AM at higher quality with the use of different MPEG-4 codecs.
Digital signal processing is used for encoding and decoding so that it can be performed by a relatively inexpensive embedded computer, with a conventional transmitter and receiver. DRM can also transmit RDS-type metadata and other data along with the audio channels. It uses in-band on-channel technology and can simulcast both analog and digital signals by operating in a hybrid mode known as Single Channel Simulcast.
DRM uses bitrates from 6.1 kbit/s to 34.8 kbit/s for a 10 kHz bandwidth and offers the possibility to use different audio coding systems depending on the bitrate. DRM broadcasting can be done on different bandwidths like 4.5 kHz, 9 kHz or 10 kHz and 18 kHz. Coded Orthogonal Frequency Division Multiplexing (COFDM) is the modulation used for DRM. DRM allows broadcasters to enjoy increased interactivity and connectivity with listeners and provides additional revenue streams for commercial operators.
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